Basic Mikuni Keihin Slide Carb Tuning ✔
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- เผยแพร่เมื่อ 28 ม.ค. 2018
- Want to know what those screws and jet needle slots do? Tuning Mikuni piston slide carburetors, the basics. A clean Mikuni carburetor with a properly adjusted float valve will perform very well. Main and Primary Jets may be changed out to suit conditions or loads, but these are the basic adjustments and what they do.
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I cannot wait to get home to see if this is what’s going on with my motorcycle. I have been on the Internet for weeks until I came across your video and it all makes so much sense.
What is your issue?
@@contact4mwy7 I think it’s running rich. The spark plugs that are less than two weeks old are black, It bogs down every time I accelerate and can’t seem to get it past 55 without it hitching forward. When I come to any type of incline hill, I lose all power as if it’s starving for fuel.
@@michaelramsdell3251 it could be starving for fuel on the inclines, or getting too much fuel which will also rob power. If your carburetor has a needle with grooves in it you should move the clip up one notch, maybe two. Try it after any adjustment to see if it has improved or made worse.
@@contact4mwy7 not sure if my needle has groves or not it’s not the original carburetor for the motorcycle. I’ve been trying to adjust the fuel air mixture by ideal air screw. If it doesn’t have grooves, is there another way to adjust the slide needle? I own a 1982 Kawasaki 305 CSR with Mikuni 28 carbs.
@@michaelramsdell3251 if it doesn't have grooves, see if there is a 'shim' lifting the needle up higher. Remove the shim if there is. This isn't the original carburetor, is it the same as the original? Has the size of the carburetor changed?
The way you simplify and explain things is exceptional 💯👌
I like this guy keeps things very simple names prices properly as he goes along.
Just like many people that watched this video, I too had same symptoms and used your video to adjust the needle, and wow. The machine (94 skidoo 583) is back to being on-fire. It rip like no other, and is a blast to drive again. Thank you very much for posting this great video.
U have the absolute best video on tuning carbs
the best carb video ive ever seen..thank you
Thanks for the advice, I can now adjust my needle aswell cheers
This has been one of the most useful videos I've ever watched. That carb looks identical to the one on my 87 Arctic Cat Jag 340. Just rebuilt the carb and fired it up. Runs very nice but I didn't know what those notches were for. Very helpful
I don't feel worthy of that comment, but thank you!
@@contact4mwy7 last night I stopped my Jag 340 deluxe to move that clip up another rung and, wouldn't you know it, I dropped it. I looked and looked and eventually I was able to find it with my magnetic pocket screwdriver. It was under the engine bracket. When I heard that click from it hitting the magnet, I was ecstatic. Moved it up to the top ring, and she ran so good I almost fell off when I juiced it. I rebuilt the carb early this month and pressure washed the entire snowmobile with super hot water. Spent several hours yesterday cleaning putting everything back together and it runs so nice now. Not bad for having sat outside collecting pine needles for 15 years while I soaked up the sun 1600 miles away. Thanks again.
@@pantherplatform That is AWESOME!! Do yourself a favor and pull the plugs every now and then to check on the mix conditions. You do not want to see those plugs with a whiteish chalky look on the ends. Ok? Otherwise, ride on!!
@@contact4mwy7 thanks for the great tip. When I started it yesterday for the first time in two weeks, the plugs were caked with crud and one fouled out right away. I put two new NGK BR8ES plugs in there and made a few test runs after each carb adjustment. New fuel pump, fuel lines, pulse hose, removed and cleaned gas tank, the whole bit. Installed aftermarket air filter and it seems to be working great. Handles the deep snow just fine. Before it didn't have any power and now it ditch bangs like a pro.
Thank you thank you thank you. The needle was the problem with my carb and why it wouldn't run right. Great video, and thanks for helping!
Glad to hear it helped! Thanks for the comment.
Great video, no bullshit , right to the point in an easy to follow way !
Excellent explanation. Very thorough. Thank you.
Thanks, the right information at just the right time...
Thank you man, right to the point! Excellent
Mycket bra informationen lättare fatta med video
Excellent video! Thank you for doing this ..
This is what I needed to watch
Well done, I'm a diesel mechanic by trade but am a bit in the dark on the carb tuning on these two strokes. You make it look easy. Great information, thanks for taking the time to share your knowledge!
Thanks for explained very clear the needle clip and idle turn slow and fast runs
Wow, what a great video. I'm hoping that the carb on a 1996 indy 440 is similar. I had to stay on the throttle to try to keep that sled from "bogging" while I rode last weekend. Can't wait to check the plugs and settings before further disassembly of the carb. Thanks very much, your explanation was very informative and properly paced.
Sounds like what I went through, especially if it was on a warmer than normal day. Check those plugs first, they will tell you what is going on inside. If the are black and soot covered, too rich. White powder coating? Too lean. Thanks for watching my video, keep me posted.
Thank you for explaining
New subscriber! Great explanation. Thanks for sharing your knowledge!
Thank you so much for this video, for the past few days I’ve been working on my Suzuki gs500 and it’s been running EXTREMELY rich to the point it wouldn’t start. Runs great now, much appreciated!
That's awesome, and I really appreciate your feedback! Here's hoping it stays running great like it was intended from the factory!
Mark Young - Outside The Box hopefully lol. Just sold my gs500 a few days ago. Now I have a tl1000r
Did you change the sizing of the main jet as well? or just changed the clip placement on the needle?
I loved my 88' Indy 340 Sport.
I have one it’s runs non-stop
@@alexbittle2900 I found and bought a 1990 Indy Sport GT. 340cc. 👍
Nice vid. Anyone can understand what to do because you explain things very well... I think a spare c-clip or two in the tool box is in order!
Thank you!
Thanks Mark!
Very helpful 🙏🏼
Great explanation......thanks !
Very excellent!
Awesome, thanks. I'm never comfortable playing with carburetors, afraid to fuck shit up. But you sure explain things good.
These Mikunis are so much better than the old Tillotsons, eh?
Great Carb info
Thanks, Dan!
Great info. Thanks!
Glad you like it, good luck with your tuning!
Cant thank you enough. The most descriptive carb video ive ever seen. Really appreciate it
Thank you for saying so, Bobby!
Thank you for this video I just learned why my carb caused my bike to rev all the way out after I put that clip in upside down after adjusting the needle
I hope you fix it, that doesn't sound like fun! Do me a favor and try setting the clip in the third groove and see how it runs and pulls for you.
Thanks the clip I'm talking about is the one that you said holds the throttle cable in. It's on a 1973 suzuki ts 250r. If I have any questions I'll be sure to get up with you
THANK YOU SOOOOO MUCH!!
Thank you so much
Nice video, i will aplay this to mye MC.
Another outstanding vid from ol sharky. While I'm in there monkeying about ill pull the choke plunger clean and apply thin white grease replace and drain bowls to be sure no water great explanation though love it man
Thanks Brent! I replaced my choke plungers a couple years ago thinking they were to blame for the cylinders loading up with gas. Turned out to be a cracked diaphragm in the fuel pump that was sending fuel down the impulse line directly into the crankcase. Doh!
Mark Young - Outside The Box diaphragm cracked due to water that turn to ice non-ethanol fuel only for the two Strokers!
Could be!
Good info..thanks !
A good channel+!
Thanks for the info I have a 488 Polaris trail indy love the sled.
Simple... Subbed
Thanks for sharing new friend here sending my support
Mechanics call those "Jesus clips" Because if you put it on wrong and it flies across the shop or into the snow,
You say "Oh Jesus" ...keep extras ..specially if you're on the trail.
Thanks for the Vid.
nice explanation currently messing with the jetting and needle on my vm22-133 slapped onto a lifan 125cc
UnderAge Moto sounds like a nice project. Keep working at it and read the spark plug shades to keep track of how it's tuned. Good luck!
thanks bro :D
New sub great channel . Followed your vid on the chock adjustment worked like a charm thanks .
I have a 79 John deer trailfire 340
Cylinders one carb , when sitting on it the right cylinder has a nice coffee color where the left cylinder is very lite tan is it common with these setups for one cylinder to do that since they share the same manifold ?
Haven't had it out because the lack of snow .. just revved it and let it idle for a bit ..
I put an open air filter on it ..
And I tried adjusting the air screw , it seems to run the best 1/4 turn out .
If I slowly turn the air screw out it starts to die and gets boggy when I turn it in the idle comes right up and seems to run decent at least better then when I turn it out I would say ...
My air screw is on the back of the carb..
The fuel pump looks original as it's riveted to the body
Is it possible I have a weaker spark on the left cylinder ? Or since they share the same manifold this is common ?
Off idle it screams
Any advice I would appreciate your input thank you ..
Thank you for being a new sub! I'm no expert on this, but, based on what you described and what I have seen and heard from others working on sleds, this sounds like you could have an air leak through a seal somewhere on that left side cylinder. Most likely it is either a leak through the main shaft seal (where the crankcase sticks out of the motor, and often the left side has the primary clutch mounted on that side), or it could be a seal/gasket that is between the two halves where the crankcase is bolted together. Also check for head gasket and intake boot leaks on that left side. Sounds like the right side, with that coffee color, is tuned right. They say if you take the engine apart to do anything, replace ALL seals and gaskets with new even if they look good, so that you're not taking it apart again to replace one you thought was ok. I hope this helps. Search for videos on main seals and crankcase gaskets.
Mark Young - Outside The Box thank you for your input I appreciate you taking the time to go over a few things
I am gonna check the things you mentioned for sure . Hopefully we can figure this out .. it's an old sled but has sentimental value gonna try and keep this thing running as long as I can 👍🏻
Good luck to you, the world of old snowmobiles needs more like you out there!
Mark Young - Outside The Box thanks mark I appreciate that!
Parts are getting hard to find for these baby's !
If it's a really old sled it's 99% sure crank seal leaking. if you ride it like this what you will do is burn a hole in the piston or to run even leaner and score the hell out of the cylinder. so that needs to be fixed before you do anything otherwise you're going to cause more damage.
You said "Thanks for watching this video, hope it helps." I'd like to say, "Thanks for posting this video, it's VERY helpful." Just so you know I've got a new KX500 with a Mikuni carb and have already raised the clip to the #1 position as I'm at 1,850 metres (6,070 feet) altitude and with temps sometimes exceeding 30 degrees. What I can't do is ID the carb: it has W6 above 91 stamped on a small-sized disc on the LHS and V31 above a 0 on the inlet side just below the choke. Anyone that could help with ID would be much appreciated.
Thank you for the comment! I don't know what year your Kawasaki KX500 is, but I did find a post that mentions the Keihin PWK 39 as the "stock" carburetor. Maybe this website will help you further identify your carburetor and its parts: www.keihin-na.com/aftermarket/pwk/
@@contact4mwy7 Mark, thanks so much for your swift reply. You posted this video nearly a year ago and are still keeping up with replies - no easy task. Thanks for sending the link as well. Unfortunately my bike doesn't have a Keihin PWK carburettor. The KX500 is an '87 with a "C" engine (excuse my language but I've heard the '87 C described as the "bastard bike", since so much is unique to that year and that year only). The Mikuni is a round slide carb (the piston has a stamp: a box inside a box - same as your needle - and 3.0), as well as a similar plate with lip beneath the "slinky coil" spring, except it's also held in position with two tiny brass crosshead screws - very awkward to work on. I'm unable at present to get the float chamber off as I don't have a JIS screwdriver and the Phillips is just camming out. The weirdest thing is the main jet has had fine copper wire wrapped around and through it, which looks like a bodge to reduce the size of its bore. (I'm an Englishman living in Mexico, so I've come to expect some unusual practices). Once I do get the bike fully up and running I'll be carrying out a plug chop straight away. Thank you once again. I've subscribed in order to hear about any more useful videos you might be posting!
@@jonniebyford that is a bit strange for a Mikuni carb indeed. It sounds like you are getting to know it well enough, though. Yes, plug chop will tell the story of what's going on with the fuel air mix. That piece of wire sounds homemade alright. Sounds like something I would have done, lol. Keep me updated. I try to answer all posts because I am annoyed by those who post a video and then don't answer questions. Plus sometimes I learn more from people like you, friend.
@@contact4mwy7 What can I say? Thanks again I guess! I have actually spent all day online trying to find info. A guy on KXRiders.com had the following to say: "The problem I ran into was nobody knows anything about this carb, it appears to be a one off type carb made for Kawasaki. I contacted Mikuni and they were unable to help with this carb as far as jetting is concerned." As far as the work goes I am capable as I was an auto mechanic back in the England in the early '80s, but parts are plainly going to be a big problem. To give you an example someone has fitted an exhaust off another KX model and actually cut a bracket off the frame to make it fit - typical Mexican practices.There is nothing locally or even on mercadolibre (Mexican version of ebay) either. Many US suppliers are unwilling to send stuff to Mexico, and to give you another example a simple letter once took 14 weeks - by signed for registered post - to reach me from the UK. However I shall definitely keep you posted and have decided that wherever I go the KX goes with me. Have watched your video on your Yamaha 4-wheeler - also very interesting! All the very best, Jonnie B
@@jonniebyford that 1985 Yamaha four wheeler still runs like a top today!
I have a DB10 and DB14 with a Mikuni 19mm Carb. I've been messing with both carbs for 3 days and am still getting a bogging in mid rev, but I managed to get it to where it is at least rideable.
The DB10, however, is dying at sudden throttle, or if you slow rev up and let go, it dies. Could I get some help on what to do?
I've had to move the clip on the tapered needle jet to the 2nd top most notch to get them to start at all. Should I move it to the very top on both? Or will this be too lean? How do I know when it is too lean or too rich?
The clip position on the needle relates to the mid throttle, 1/4 to 3/4 open. If you have a bog in the mid range it is due to being too rich or too lean. If the spark plugs don't show up as really dark or really light coloring on the ends, you may have to experiment with the clip position to find where it runs without the bog. I have experienced the too rich (clip too low from the top setting) bog on my snowmobile in warm weather, so I know it can happen. The air screw adjusts the fuel mix at idle and to 1/4 throttle when the needle takes over, so adjust the air screw at idle until it seems smooth. You may have to increase the idle screw to speed up the motor just a little bit to help with that adjustment and then back down to a good idle speed. The manual on mine says to start with the air screw one turn out from being all the way turned in, but go easy, low pressure on the screwdriver or you'll damage it. As for the motor that is dying out on fast throttle, that could be many things including plugged fuel passages, floats issue in the bowl, low fuel pump flow, etc. If the intake gaskets are good, a thorough cleaning of the carbs and check float settings is a good start.
So my hmf kit says to set at 1/4 which line should i move the clip up to ? Im installing a 110 jet
I'm confused on what they are referring to setting at 1/4. The needle has 5 rings on it, so to me they would say set to ring 1, 2, 3, 4, or 5.As for the relationship with a 110 jet, I would have to trial and error the mix setting by checking the color of the spark plugs as I do not have a formula or chart for that. Let me know what you find out?
awesome channel im needing tips on 74 kawasaki f7 175cc 2 stroke so i found ur channel
Danger Davefpv thanks, man! Keep 'em tuned right and they are a blast. Nice quad in your profile pic.
Any advice on starting adjustments in cold weather? Runs great when warm but takes a lot to start. I will try to adjust the air screw when it is warm enough to start (above 7 Celsius).
I would turn the air screws in a quarter of a turn and see if that makes a difference (make it run just a bit richer). What is the idle speed when it's warmed up? Could the idle be turned up just a little more? If this is an oil injection sled it is using mostly the fuel as lubrication for the Pistons and internal parts, so a little bit Rich on the idle may be more beneficial than too lean.
@@contact4mwy7 it's actually drz(bike) that is a four stroke (so it has a fuel screw not an air screw). When I get time I want to adjust the needle valve and perhaps replace it with a richer one. I do want to use it in the winter. Thanks for the quick reply.
@@jessd1952 if it's a fuel screw try turning it out a quarter turn before cold starting it the next time. See if that makes a noticable difference. If not, go another quarter turn out. If it makes it worse go a quarter turn back to where it was and add another quarter turn in from there and try it. Trial and error, but you should be able to dial it in to a good starting bike through the mix screw and idle screw. Remember to check your spark plug now and then to see if the bike is running too rich (very black and sooty looking).
@@contact4mwy7 I haven't even looked at the spark plug but plan on replacing it. If I can't tweek it to start it I will look into replacing the starter jet or the needle jet. But like I said before it runs great with occasional sputter when idling.
I turned it the fuel screw and turned up the idle. It does start better now but still isn't great. Are their particular spark plugs that run better in the cold?
Thank you. I recently bought a Harley Ironhead 1000 with this carburettor. I think I'm going to change the Carb but this helps tuning for now. Where is the air jet setting?
Hello! Are you asking where is the air jet screw or what is the initial setting for the air screw? It should be on one side or the other, flat blade type. Gently turn it as though you are tightening it until it stops, this means it is fully seated into it's bore. You do not want to over-tighten this screw or damage can occur. From the fully seated position, note the alignment of the flat screwdriver groove. Turn the screw as though to loosen it 1 turn from there. Start the bike and check how well it is idling/starting. You may try turning the screw to loosen another quarter turn and note what difference that makes. If you adjust the screw out too far the bike will idle lean and possibly make for hard starting, maybe even cause it to hesitate off idle or when you try to rev it up. Let me know how it goes?
@@contact4mwy7 got it.. I've done some research.. my carb is a VN38-9 Mikuni with 4/042 330 main jet, Q-2 needle. It's setting for air jet is idle only. I'll carry out my tuning from elevation, 140ft asl @ am temp. 50°f = 300 < 330 main jet on 75% throttle. Thank you.
I got a 28mm flatslide mikuni and having trouble tuning. It bogs on fast Acceleration. Two questions if turn the air mixture screw all the way in and it don't bog out, do I need a big pilot jet. And do that affect my needle jet settings.
I think you are on the right track. Turning the air mix screw 'in' would give it less air/more fuel, so this could very well indicate that you need a bigger pilot jet. I would suspect that the needle jet may also need to be increased to match. You might be able to add more fuel from 1/3 throttle to full open by moving the E-Clip down the needle from the top if you still have grooves available. If you end up in the last groove down and it is still running lean you will have to increase the size of the needle jet. The spark plugs will definitely tell you where the mix is from lean, to rich, to just right.
Had a #15 in and it did nothing, tried #20 it still didn't cut off my ENGINE but by turning it out my idle increased. I have a 17.5 that I haven't tried but if 20 don't cut it off I'm thinking bigger. The largest they come is #22.5 and #25. Another thing if I bog it out it take 10minutes to pull start it back up. It usually starts on the first or second pull but after it runs hard to start.
@@jeromesims2939 Is this out of the ordinary for how it usually runs? Make sure there isn't any blockage in the fuel passageways and that the floats are properly set too. If it seems weird that it is running this way when it didn't used to, it could be something inside the carb?
1994 488: Both my carbs were on position 3, one of the needles had position 2 apparently ground down. Seemed to be purposely disabling that position. The clip won’t attach there at all. Perhaps an aftermarket thing? Anyway, great video, still working on mine. Thanks.
If it runs strong in position 3 and isn't turning the spark plugs black as coal, run with it. ?
My factory setting was on the midldle and move it to 2nd position. I based lean rich or lean via fuel consumption.
I used to base it on sound and how it felt but I found out I was wrong in doing that instead of looking at the spark plug ends for black (rich) brown (just right) or white (lean). Happy sledding to you my friend!
You are correct the middle position is the factor setting for a needle adjustment that's the way the factor runs it. The factor makes it where you have 2 adjustment up or 2 adjustment down. I just read my owners manual on my banshee so atleast that is how Yamaha does it
Hello,been reading the comments for over an hour trying to find my answer. Great video by the way. Quick question,I have a new mikuni vm22. Clip is in middle position. I tried tuning all day today. It keeps wanting to slightly take off in idle and will almost completely die when I give it gas. Should I raise or lower the clip as a starting point. Is my situation to rich or to lean?
Thank you very much!
The clip on the needle adjusts the mixture from about 1/4 throttle through 3/4 throttle. The air mix screw adjusts idle mixture up to about 1/4 throttle. The main jet adjusts mixture from about 3/4 throttle to wide open. What year is this machine? Is it 2 stroke or 4 stroke? Single or twin cylinder? Have you pulled the spark plug to have a look at its color?
@@contact4mwy7
It’s on a hemi predator 212cc. The fake mikuni I took off was running very rich as the plug was completely black when I took it out. I bought the real mikuni so I can really get into tuning these things and make sure it’s right.
My motorcycle idles great with clean jets and new vac lines and all. It dies upon throttle unless i spray the carbs then itll rev normal. Plugs are black, I thot it was lean so I pulled tge needle up one, but should I try the lean direction and put needle down more?
Well Shane, you shouldn't have to spray at all. So let's see, how many turns out is your air screw? Does it continue to rev after you spray it or do you have to keep spraying it? What product are you spraying into it? Black plugs usually mean it's too rich, yes, but have you had it running enough on its own without the spray for a good plug indicator? If it dies when you crack the throttle, it's usually a sign it either isn't getting enough fuel or too much. Which groove is the clip on the needle? The main jet is screwed into the bottom center of the carb inside the float bowl. Be absolutely sure the hole is clear with no obstruction. With ethanol fuel I have found groove #3 from the top works best.
I have a machine that idles good when it's cold but as soon as it warms up it gets boggy in the bottom and stalls and the only way to start it again is hold the throttle wide open and pull it many times but once you get it revved up it's fine again until you let it idle down then it will stall again I've cleaned the carbs and still no difference any idea what would cause this
The part about having to hold the throttle wide open to start it up again suggests it is getting too much fuel at idle. There are two controlling factors for that. The size of the primary jet, and the adjustment of the air screw on the side of the carburetor. Noah, gently turn the air screw (not the idle) in until it stops and count how many turns it takes to do that so we know how far open the were turned. Is it 1/2 turn? 3/4 turn? 1 and 1/2 turns? Write down the number of turns in it goes until it stops, and again, be very gentle with that screw so as not to ruin anything. Let me know what that number is. If the air passageways are clear, turning the screw open (as though you are loosening the screw) should add more air to the mix and solve your low end bog and stalling issue. If they were 1 turn out to begin with, put it back to 1 turn and add another 1/2 turn to it (or them if this is a twin) to make it 1 and 1/2 turns out total. Still not good? Try 2 turns out. If you go 3 turns out and it still idles the same, it may be either a blocked air passage, or that the primary jet size has been changed to one that is too big allowing too much fuel. Next time it stalls, remove the plug(s) and see if they are shiny with gas, or really black with soot. If this is a twin, are they both shiny with gas, or only one? If so, which one? I had an issue with mine loading up with fuel and found out the pulse hose that goes to the fuel pump was dumping gas into the crankcase due to a cracked diaphragm in the fuel pump. I had to remove the hose from both the fuel pump and the crankcase to check each end and that's when I tipped it up and gas ran out of it. I rebuilt the fuel pump and that took care of that.
I think your pilot jet is too big or air screw is too close.
I installed new mikuni on xr100r indels bogs all the time help plz
sorry idles great bogs 1 turn or 2 doesn't matter
no intake leaks could it be slide needle stumped
I can't seem to find the stock setting for a Mikuni BDST38. The manual for the bike lists the jet needle position as "5CEW9". I can't find anywhere what that means. 2nd position? Who knows. But, I was wondering if all mikunis pretty much come stock with the 2nd position like what you show in the video.
I can't confirm that, but start with the 2 or 3 groove and run the machine to see how it feels, and after a time of running it pull the plug(s) to check it's condition of too lean, just right, or too rich. Too lean? Move the clip to a notch closer to the middle of the needle. Too rich? Move the clip to a groove closer to the top end of the needle. How's that? The clip position will always relate to the temperature and elevation above sea level at the time of operation.
@@contact4mwy7 that sounds right. The guy I'm helping was starting from scratch. I have the manual, but it doesn't say the standard clip position. Thanks for the reply!!
Take your time and good luck to you both! The clip position affects the throttle from 1/4 to 3/4 throttle ONLY. Keep that in mind for tuning.
Can i do this on my enduro ? I want to go faster and i want to move ring down to get more fuel, is there posibility to ruin my bike?
You can experiment with different ring positions, but keep track of what your results are not just by the feel or sound of how it's running, but by checking the plug color. Too lean or too rich is not good for a motor and could lead to bad things. Thanks for asking.
Did the VM 30 s for my Honda CM 400T rebuild. It starts ........awesome .....but with the choke levers down and and maybe for 3 or 4 min. it runs and quits. Now i gotta turn screws or something ?
Could be a fuel delivery issue. Are the carb floats set proper? Can you confirm decent flow from the fuel tank? The air screw should be at 1 turn out from fully closed. You may have dirty passages blocking fuel also.
Mine is bogging on the third the secound and first it iddles perfect on all and starts as well but as soon as I hit that throttle hard it dies out should I try the 4th and 5th position of the middle clip?
I would check for something plugging up the main jet fuel channel. It might not be getting any fuel other than idle? Otherwise check the spark plugs to see if it's really black and sooty which would mean it's getting too much fuel for some reason when you move the throttle. You should have noticed a result when changing from one groove to another, but since you didn't I don't believe it's the groove number that matters but something else in the carburetor that doesn't belong. A good cleaning may end your troubles.
Thank you!!
You're welcome!
So u want it to be at the fastest idle? I don’t understand that because I’m only supposed to idle at 1500 rpms so if I go up that’s not right?
Let me clarify that, Bryson. You want to adjust the air screws in and out to find the setting where the motor idles the fastest. When the fuel/air mix is just right it will make the most power which translates to the fastest idle you can get from the motor without turning the idle screws (yet) or using the throttle. Be careful not to let the idle get high enough to engage the clutch. If that happens be ready on the kill switch until you can turn the idle screw(s) down or better yet have the track off the ground. Then, once you find the highest rpm by adjusting the air screws, adjust the idle screw(s) up or down to reach the desired rpm setting for your sled. Does that make more sense?
Good I go. I've had a big in my bike and very hot exhaust. Sounds like it was too lean or had a plugged idle circuit or jet.
Pull the spark plug(s) and note the color on the ends. Very pale, white chalk looking ends would indicate a too lean condition. Brown shades are preferred. Black soot coating would indicate too rich condition. Make small adjustments if needed to make any corrections and check your spark plugs again after running the engine for a time until it is right.
The air screw is it the same factory setup (one turn) for the mikuni vm24ss
I believe so, set it there and see how it idles and starts.
Its doesn’t show this in the Yamaha Kodiak service manual. Good to know
where is the factory spec for the idle screw with the spring on it?
Disgusted Batman I do not know 5hat there is one. The idle screw should be adjusted so the machine idles somewhere between 1500rpm to 2000rpm in most snowmobile applications.
Same procedure for a 1998 Polaris 600 triple? My plugs are fouled up and it bogs a bit at times
If it's bogging from quarter throttle to three quarter throttle, it's your needle clip setting. Where your sled is 10 years newer than mine, you may have the double Phillips screw setup on a retaining plate to remove to get to the needle and clip. Try a clip setting one groove higher towards the top. The air screws can be backed out a quarter turn or so to add more air to the idle up to quarter throttle. Wide open throttle is controlled through the size of the opening in the main jet. Always check your plugs to verify your fuel mix ratios.
@@contact4mwy7 Thank you for the excellent video. I will check the clip. I am afraid to lean it out too much and burn up the engine. All 3 spark plugs look black and sooty.
@@dtaylor5493 you're on the right track and being cautious, which is good! Keep checking the plugs from time to time. A chalky white look to them is too lean.
Quick question. Have a brand new four stroke that’s running rich and smells like fuel. Should I wait a little to break the motor in before adjusting the clip? Bike runs good, just stinks of fuel when running and the new plug is super black.
Sounds like it's getting too much fuel alright. As for brand new engines I don't have much experience, lol. If it's a Mikuni type carb I would check the turns out on the air screw and the c clip position on the jet needle. If the air screw is turned out a bit more it will add more air to the fuel at and just off idle. If the c clip is set at anything lower than the very top groove you could try moving it to the next groove up, towards the top. This will add less fuel from 1/4 to 3/4 throttle.
@@contact4mwy7 thanks for the quick reply! I will check the air screw first! Then move onto the needle clip. Bike does run good, so I don’t think it’s the main jet yet! Just wreaks of fuel.. even my clothes smell like an exhaust after 5 mins.. 😂
HI thanks for the video. Does needle position affect idle speed at all? My Honda CT110 will barely idle and I have a limiter cap on the air screw so I can only turn it about 250 degrees. I am running rich with black soot. Idle screw has to be ALL THE WAY in to idle-that can't be right.
Needle clip does not affect idle. If it's running rich enough to turn the plug black, it sounds like you have something going on that needs to be corrected. The first thing I would check is if the float/needle system is shutting off fuel from coming into the fuel bowl when it's full. ? Can you shut the gas valve off and run it until it stalls to see if it comes out of the rich flooding condition?
@@contact4mwy7 I cleaned the carb and set the float hight to spec using a caliper/ruler. So to be clear I need to start motor, shut off fuel petcock, let engine die...How will I know if I am coming out of the rich fuel situation? TY
@@MrJammor After shutting the fuel off, if the engine starts running better, rpms increase, then you likely have an issue with too much fuel getting into the float bowl and overflowing. You said the air screw had a lock on it so that it can only turn so far each way, when you turn the air screw back and forth does it make a difference in how it runs?
@@contact4mwy7 Yes it speeds up as the bowl drains AND it allows me to back the idle screw out 1 to 1.5 turns, maintains idle, then revs high and dies as the bowl empties! So I took the carb off. While holding carb at a 45 degree angle my float was not parallel to the carb body- the non-needle end of the float was higher. So I bent the tang which brought the float parallel- now I have the same problem and realize I must have bent the float tang the wrong way! Finally you asked if the pilot screw does anything- and it doesn't. I am going to replace that screw with a non-limiter screw so I can turn it 360 or more. Thanks for your help and I will let you know after I mess with the float again. Finally I checked I've got a great spark and no clogs in air intake-clean filter. I do believe I actually ruined one plug with excessive gas. I have heard that was possible but had never experienced it.
So the limiter screw is a fuel metering screw- I replaced it with one I can turn either way as much as I want. It still does not seem to affect anything. Set the float pretty high to try and force a lean condition and it still runs very rich. Perhaps this fairly new plug is failing from too much gas? I could try a new plug. Not sure what to do next. If the needle or seat were severely nicked or damaged causing a 'failure to seal" situation I would think the fuel would run out all over the ground with engine off and petcock on-but it doesn't. Perhaps I could clean that Keihin again. Open to suggestions :)
Hey Mark, is the needle adjustment a final touch tweak adjustment? (after finding the right main jet size). or is it at the same adjustment stage as finding the right main jet size? Amateur here 😄
I'm not an expert on that, but I would say if you have the needle as rich as it will go and the motor is still lean (read the spark plugs) then I would up the main jet size. There are charts to show what jet size is recommended for altitude/temperature. Read your spark plug colors.
@@contact4mwy7 i have my needle as rich as itll go, and the spark plugs read just right. should i bother setting the needle to the middle and put in a bigger sized main jet? Im in a pretty hot area and only once in a while go up cold mountain areas
If the spark plugs look proper and it's running good, I'd go with it as is. Higher elevation and warmer temperature would need a leaner mix, low elevation and cold temperature would need a richer mix.
@@contact4mwy7 ok Mark, ill stick with the current adjustment then. Thanks for replying!
Stuff an 1/8 inch drill bit through the jets now 👌 I promise it’ll be a complete rocket it’ll just never make it from station to station 😂
Lol, "Your gas mileage may vary." 😂
My bike will only rev up with the chokes on, it won’t rev with them off. It just goes blahhhhhhhttt and dies. The plugs have always been very sooty and black, which tells me it’s too rich. Since the Mikuni starter circuit is different from a standard choke, is it giving me more air to the mixture while it’s on and throttle opened? Which is why it can then rev with the choke on? With the throttle closed, it will barely idle with the starter circuit on. Been chasing down the tuning with these carbs for weeks. Air screw is almost falling out to achieve a rise in rpms; I have smaller pilot jets on the way. Any help would be greatly appreciated. Honda 400cc with Mikuni VM 32’s.
Tim, start with gently turning the air screws all the way in until they bottom out, don't force them past this point! Next, back them out 1 turn "open." This is the ballpark for idle and lower throttle openings. Put clip in jet needle in the third groove down from the top. This should be rich enough for Ethanol fuels (which your bike was not made to run on). IF it doesn't run properly with these settings, you have other issues at play. Most likely a plugged main jet. Possibly a float height problem. Fuel delivery from the tank restriction. Something along those lines. It shouldn't be running only with the choke on (actually a fuel enrichment system).
Mine came factory in 4th position, had to put in 5th clip for it to run right from idle to 1/4
How do you tell if you're running rich or lean on the needle or the main jet?
By the feel of how the motor is running is one way, but checking the spark plugs color is the best way. White to a very pale tan shows lean, black shows rich. You can even get very scientific and study the porcelain cone inside the barrel of the spark plugs for certain colors and lengths. I generally shoot for a dark brown color on the plugs, which is a bit on the rich side and will lower the flame temperature somewhat as you go richer than stoichiometric 14.7:1.
If the float level is set proper, yet I still get fuel into the oil/crankcase, could the needle be the problem. I bought someone else's mess. Also how do u adjust the idle speed screw? All the way in and 1 turn out again?
Hello Len. If the height of the float is set correctly yet fuel ends up going right through the carburetor anyway, it could be that you have dirt or crud in the opening where the needle seats to close off incoming fuel, or the needle itself lost the ability to seal it off and you need to replace it. Other than that I do not know where your fuel problem could be coming from otherwise. Are you asking about the idle "mix" screw? If yes then generally you do turn it all the way closed, gently, and then back it out 1 turn for a good starting point. This is an air mix screw, not fuel. Out means MORE air in the idle mix and just off idle, In means LESS air to the incoming fuel mix.
@@contact4mwy7 I adjusted the needle to what you call factory setting. That did a great job. I as asking about the idle speed.. How do you adjust that screw? It's the one w the spring on it I believe. All the way in and back out 1 turn as well to start?
No, that would be too high speed. You are just going to have adjust it from out to in until you have a good idle. Be ready to shut the motor off if it is idling too high and back it out some and try again. If it won't idle at all turn it in and try again.
@@contact4mwy7 you're the best. Thank you for taking the time for me.
On my yahama four wheeler my needle came out but no ring around it like your
That sounds odd to me. I'd it running normal? There should be a "C" clip in one of the grooves on the needle. By the way, can you tell me where the serial number is located on the Yamaha four wheeler?
good evening I have a yamaha rd125lc after 8 thousand rpm clogs.whats wrong. Thanks
Hello! I'm not familiar with the rd125lc, but I have to wonder what it's rev limiter is set to, as that's what sounds like is kicking in?
u start with 1 1/2/ thats the basic for 2t. for 4t 2 1/2 turns out.pilot jet u should also adjust if need it then needle and mainjet.u have also different type of needles.
Setup does vary, but this is a good starting point, I hope you agree?
I did that and the ring flew and disappears as by Magic Art, I never found it anymore. In case put a hand or a rag on top in case.
Carlos A. Ramos Santiago I'm sorry to hear that your clip flew off. Good tip on using a rag or your hand to cover it to keep it from flying off. I hope you can find a replacement from a snowmobile or small engine shop, hardware store or auto parts store. Bring the needle with you and be careful not to lose it.
Mark Young - Outside The Box ,,,,,,thanks Mark I will do that
get a flat head screwdriver and place the face of it against the clip and hold ur finger on the other side and push, it wont fly anywhere, same to put it back on
Basic tuning, to be used in conjunction with cleaning the main jet. Pilot jet tends to plug with ethanol fuel, works with the air mixture(1 turn out).
Synchronize the carbs for a complete tune up of fuel system.
My XR400R does the same thing. Gonna check the needle! So, if its running rich, I want to move the needle DOWN to allow more air, is that correct? One thing I don't understand, is if the machine was running fine before, why would the needle have to be adjusted? 😒 🤔 😒
Hello David. Moving the needle down will make it run richer from 1/4 throttle through 3/4 throttle. It would raise the needle allowing more fuel to flow into the air stream. The clip really depends on where you are elevation wise and the average temperature of the air when riding. Really cold air or low elevation could use the needle set in the number 3 groove, and really warm air or higher elevations could use the needle set in the number 2 groove. The best way to dial it in is by feel from 1/4 through 3/4 throttle, and taking out the plugs after a good ride to see if they are white and chalky (too lean) or black and sooty (too rich). Also set your air screw a tad rich (around one turn out from all the way turned in) generally speaking. This will allow for easier cold starting and cooling the motor down when you're off the throttle at idle. How's that sound?
@@contact4mwy7 Well, I moved it from the stock 3rd ring to the 2nd ring and this helped. But I'm confused because I thought I had a rich condition. It's a lot better now and I'm in Sacramento CA. It still had some hesitation so, I pulled the snorkel and now it's pulling like it should. However, after two carb removals, sometimes I think it's just bad gas lol! 😄 ... So, if I want to put the snorkel back on, should I put it on the 1st ring or the 4th ring? This is a little frustrating because I plan to ride at 7000ft this summer ...
@@contact4mwy7Maybe I misread the spark plug being rich. It was black around the outside, but the tab looked normal.
Remember it like this, the lower the number of the groove means less fuel will be added. Groove 1 (closest to the end of the jet needle, the tip) is Lean. Groove 5 (towards the middle of the jet needle going down) is Rich. Black around the perimeter and normal tan/brown on the electrodes is better for your motor and gives more power than tan/brown on the perimeter and chalky white on the electrodes.
I don’t know about Mikuni’s but not all keihin’s have grooved needles so for those if you need to modify the needle high need to add very tiny washers
Thank you for sharing that info.
My idle screw isnt doing anything all way in or out? Any ideas
Have you cleaned carb lately? May have a blockage in jets?
I agree with Tim, it sounds like there is a dirt or varnish blockage somewhere. There are tiny ports and passageways inside these carbs and when they get blocked it can really mess up the way the carb performs. I would remove the brass jets and find some small wire like from a wire brush to run through them gently so as not to distort the size of the holes and openings. Also into any passageways that gas or air has to go through. Blow the hole thing out with air afterwards (safety glasses!).
Also check your carb floats and make sure they are adjusted properly.
I put a 30 mm ATV carburetor with a 24 mm slide in it I don't know why they call it a 30 mm of the slide is only 24 anyways I can't get my cammed Predator 212 with a light head job to suck fuel cuz when I spit it over with a drill after about every 30 or 40 rotations it might only pop one time and it's starting to make me mad but I cannot get it to suck fuel to idle and it hardly runs off of starter fluid what do I do
Do you have a video of this machine? Does it have a good fuel pump? Is this a fuel or spark issue? How is compression when it turns over? As for the carb, I thought the mm number referenced the bore size, not the slide size?
@@contact4mwy7 it's hardly running and I checked my valves today and I think my valve guides are shot because I can slide my vows side-to-side pretty aggressively and they keep moving and I've lapped my valves four times and it's still spitting and popping
My needle has grooves but also has a tiny washer under the c clip. Hmm, I'm in the 3rd groove and have a horrible gas smell and a surging idle. I might remove the washer and try without it.
I have seen needles that only had one groove using a washer as a shim to richen the mixture, but where yours has grooves it does seem a bit odd. Maybe the washer is there to support or center the needle? It sounds like you could try it without the washer, or move the clip to the 2nd slot from the top to go a bit leaner and leave the washer on. I would want to see a diagram from a service manual to see if that washer was indeed a factory added piece.
I moved the e clip all the way down and now the needle retainer wont clip in place
Sorry for the late reply, my notifications were not coming through. Sounds like you need to find replacement E clips, soon!
no mention of slide height adjustment.
So if your going for performance. And you already put bigger jets in. Should I run the needle lean or rich?
Better to go rich than lean, Jacob. Check your spark plugs from time to time to make sure you haven't gone too rich and turned them a sooty black.
Quick question so what's better rich or leaner
Richer is usually better to bring the temperature down. Too rich will fowl the plugs. Look for at least a coffee brown color on your spark plugs. Anything lighter than that may indicate stoichiometric or leaner fuel to air ratio and could overheat the pistons, etc.
@@contact4mwy7 thanks 👍
Nice basic tutorial on mikuni carbs, but to limit any confusion, what your holding is a jet needle or slide needle, not a needle jet 😉
Lucky you still had the clip 😳thought you would have covered it with your hand 🖐🤔
How can you tell which Mikuni carb you have in order to get parts?
I have the Mikuni VM34 carbs. I got ahold of a service manual that covers all years and models of my sled and the carb sizes were listed in that for my 1988 Polaris Indy Trail with the 488 motor. Thanks for asking and good luck to you!
I'm not sure if it there are markings that identify the model right on the carb. Maybe someone can chime in on that.
@@contact4mwy7 I have something that looks like the BSR33 and it says Mikuni on it, the problem is that I dont have too many hours on it but less than 20 for sure and a couple of tanks fills later and I am noticing both hard starting and flooding within this time on my UTV! So I am wondering if it needs a cleaning or an adjustment! I am afraid to open the bottom being that I dont have a gasket on hand so I am wondering if the gaskets are universal (standard) for all bsr series in order to find the right one!
@@Hi-Tech-Ray I wish I knew more about those carbs to say for sure. Is it idling well when it does start or does it sound like the idle speed is a bit slow? Have you tried opening the air screw(s) in measured increments? Are the enrichment plungers (choke) adjusted with a bit of free play (1/8 inch at the lever)?
@@contact4mwy7 It actually was working well before I snapped the Right-angled tube (Some are straight) by the accelerator pedal of the Throttle cable where I waited a long time for a replacement. However during the wait time - it started up well with out a throttle cable! This situation started after I changed the throttle cable, However I did notice that I had to strip the cable to expose about 2CM more of the bare throttle wire for more allowance of free play being that the carb throttle was not resting in the close position which I am starting to believe contribute this problem! As for your questions I have not yet tried them! BUT I did clean the spark plug and it got wet and black again from trying to start engine!
Air screw is just for idle only. Once you set your air screw where you want your idle to be leave it.
Then set your needle or you may need to adjust your float. If your float setting is not level to the gasket you will flood your motor.
@@jasont1917 The air screw covers the air/fuel mix from idle to quarter throttle opening. If the motor is sluggish until you get past quarter throttle it's likely due to the air screw causing the mixture to be too rich or too lean. Yes to the float adjustment, very important. Thank you for your comment.
Poor throttle response has good power on take out an top end with no sputtering but has poor throttle response on fast turn of throttle what do you think the problem good be ? Any help will appreciated
Which model mikuni is this?
VM34
Amazing video really helped, but removing the clip like he shows, wasn't a good idea. I recommend using some flat pliers. Otherwise you'll end up losing the ring.
I've done it this way dozens of times. Keep your finger covering the clip and it won't fly off and disappear. :)
Had these on a Exciter SX 540. You do not want one flying in the snowbank
or under the motor loll. So do this somewhere that if it does fly out of your hands
it aint going far.
Good point, do this in a safe place that the clip won't go flying away into gone for good land!
Someway somehow my 88 Indy trail 488 has 12000 miles on it and runs like a dream
That's awesome! They were built for the Long haul it seems!
Anyone deal with this on the (clone) VM26 Mikuni carb for the chinese dirt bikes? (Hawk 250)
I have not had the opportunity to compare the two. Let me know what you find out.
@@contact4mwy7 I'll prob screw it up...I'm 19 and a complete rookie with carbs
@@liveandletlive2894 we are all a rookie until we learn and experiment. Just remember to check the condition and color of the spark plug to see if it is too rich or too lean.
@@contact4mwy7 just bought the bike with 80 miles on it not sure what its history is though now with a new carb/jets and a valve adjustment shes running fine I'm just nervous spark plug color may indicate to previous but non current conditions
The only thing you missed are the pilot jet and main jet.