1979 Yamaha xs750 carb jetting
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- เผยแพร่เมื่อ 7 ก.ย. 2024
- This is a project that I have been working on. The bike has been running lean since the removal of the air box and the addition of a 3 into 1 Mac exhaust. An update to this video, this bike is still not running perfect but you will be able to use it as a guide to get you pretty close.
I never cease to be amazed at how many people go to change jets but don't know how to get a true reading on the mixture or I guess you would call it the science of rejetting. first it's a pretty common rule pr thumb that for pods you start out by go up 6 sizes in main jets and another 2 sizes when you add opened up exhaust and for every 3 sizes you increase the main jets you go up 1 size in pilot. also to test the mixture when changing main jets you find a straight away where you can open the bike up to about 3/4 of redline hold it there for a mile or so then hit the kill switch and coast to a stop then check the plug. riding around speeding up and slowing down and idling is a total waste of time because you your plug reading is going to reflect the mixture at the last speed you rode at not the actual mixture while in the main jet circuit. you need to isolate the fuel delivery circuits and check each of them individually so i guess that would also be the science of rejetting.....
Sounds like a Technic that would work pretty well. You should help educate all the people that dont know anything about rejetting and make a video on it.
I known this is an old paying, but I just wanna say thank you for uploading.
No problem at all. I try to help people so they don't have to repeat the same mistakes I have made.
I just bought the stuff you finally ended up using. I wish I had the original air box really, but it came with these pods. Thanks for the posting man, I appreciate your time.
Thank you, and good luck with it.
Quicker, easier way to check for leanness is to pull out the choke when it is stumbling at speed. If it runs better (by adding gas with choke) it is too lean. Repeat as necessary.
unless yer chokes are leaking. Then everything is off. I had a problem with aftermarket mikesXS throttle shaft seals. they were too thin and caught air at high speeds causing my engine to race at stops/hanging up with an airleak to the carb
I own one and it has the air box and K&N filter. Never had any problems like you do. Remove the box, you get problems. I have 80,000 miles on her.
thanks very much for sharing I've just started my own xs750 build, so will remember this vid on ignition day I have also just bought a set of Triumph Trophy 900 carbs that are a perfect fit and from what I have read on the uk forums are a huge improvement in performance on the xs750
Good luck with the build, you should post a video when its complete. Shoot me a message if you run into snags with it.
thanks mate will do, maybe a while finnishing a little Honda twin at the moment so that will be 1st, cheers Rich
you will find that to avoid overheating on the center cylinder you'll need to run that one just a little rich, granted I'm running the wisco bore kit on three n one with carbs from an 850 and jetted .
Great job. I had an 79 850 special.
Thank you much. It has actually been sitting lately. I have to do some troubleshooting because it's not getting spark. Probably something going on with the points.
I have an 82 XJ-750 Maxim that was doing the exact same thing, I didn't Jet it out though, I just opened the Pilot Jets up some and it smoothed right out.
Very helpful video! Camcorders focus on the distance that the majority of the image is at (higher end cameras will give preference to objects in the middle of the frame) so if you pick an object up and hold it in front of the camera the background is still 75% of what you're filming so that's what the camera focuses on. Just leave the parts on the table so everything is the same distance away. It makes everything nice and simple for the autofocus!
Thanks for the comments and the camera tip. Im sure it doesn't help that I filmed that with a crappy camera phone.
@@Jeremybaland hi good video. my 750 se appears to berunning rich but only on one pot the outside right as you sit on the bike that plug was black and sooty do you think i could cure this by adjusting the air mixture screw? thanks
@@SEANO1810 Possibly, but before you adjust them you need to hook up vacuums gages to make sure they are all the same otherwise you are just guessing.
@@Jeremybaland thanks thats a bit above my level of ability plus i dont have any lol, cheers
@@SEANO1810 The gages are supper cheap online. Its a really easy process you just hook them up to the manifold. Im sure you can find a video on it. Owning a bike like that you will have to learn everything about adjusting the carbs or it can get very expensive. Good luck with it.
47.5 on the pilot fouls plugs after 1 week. dont go that fat. go 3 turns out on the mixture screw, and run a 43... stock jet size is 40 for the xs750
Wow,you got that up on the center stand easier then I thought possible. Mine takes 2 plp to get it up on the stand.Perhaps its bent.
hjoken It could be bent, but I remember when I used to have a hard time with a center stand. There is kind of a trick using momentum and leverage. My Triumph Tiger I way harder to put on the center stand than my XS. Thanks for watching.
love the flags!
I have a xs850 carbs that are a bit different they are H5C-34mm Hitachi rather than the xs750 with HSC-32mm Mikuni. My carbs all together have 12 jets.
Normally if the spark is black so it means that ur engine need more air not less so u have to upgrade ur pods or to have bigger ones
I use an aem wideband on the handle bars and a pyrometer on the pipes.
awesome video!.So you went up 4 sizes on the main correct and you left the pods tapped up?? ive heard the rule of thumb is 5 sizes up if you have pods and free flow exhaust. I really like how when you changed a setting and then took us for a test ride.
jay wilbur Thank you much, I took the tape off I couldn't tell much of a difference with it on.
You sir, are awesome ! :)
Thanks! I try to share what I have learned to help someone else, cause I know I have picked up some pretty good tips from TH-cam.
Lone Ranger Thanks for taking the time and going to the effort to share. The World is a better place for your contributions !
ON MY 79 XS750 special im running 145main 43.5slo jets... got that
same 3 into1, and I'm running naked uni pods (black inners) mechanical
shutoff petcocks... the vacuum stocks are trash.
Thank you for this video. Awesome
Thanks for comment and sharing.
i got cheapo ebay pods. Im too lazy to put the air box back on. I'm just gonna make due with hesitation at high rpms. I hit highway speeds fast and fine.
I wanna buy that airbox!
I bought one off ebay, but it turns out it was incomplete, missing the part that holds the filter.
Helpful video! When you moved up to your final jet size did you leave the movable rings on the needles to the last spot you moved them? or back to the original spot?
Thanks!
Ross
It's been awhile back when I did this so it's hard to remember. I believe I left needles in the highest position
Thanks for the reply! i believe i have the same pods and my bike seems to being doing the same thing....spudders out at high RPM's . thanks for the video.Lone Ranger
Hi, I would like to ask a question off topic please. I like the handle bars your using and would like to know what they are please and where to get them. Also, do they work OK with the shorter UK style throttle and clutch cables? Thanks in advance
Truthfully I dont remember. That build was many years ago. Sorry I couldn't help more.
@@Jeremybaland Thank you for taking the time to answer tho 😊
Where do you get your parts from I have a 1979 XS750 I'm restoring and need parts
Cecilio Tabor I had to shop around. Most of the stuff I got was off eBay, and some from bike bandit.
Cheers mate
Hello mate, i woudl like to know if that set of carbs can work for a Yamaha XS850? because i'm having problems with mine, and those are very rare and complex. in other hand i'm seeing that your carbs only have one jet i guessing is the main, where is the pilot or slow jet?
I think the 850 carbs would work but I'm not 100% sure. You would have to do some research. Mine had the pilot and main jet that I swapped out.
Das a 750, honestly if I were you I'd get a set of cvk's off a triumph sprint 98, headers and exhaust too.
Carbs require mild tuning and are direct fit, the headers require minimal welding to the flanges and the crossover pipe doesn't have room for the center stand.
However, makes it run quite a bit better though.
Dong Suk I wish I do a lot of things different. I don't have a lot of people that want to volunteer to give the stuff I need. I would gladly take the parts from a Sprint if you have them to give. Until then I will have to continue with just the pain Yamaha parts it came with.
David L. Do the 98 sprint headers bolt straight up to the xs750 head?
How did the plugs look after the 150 jetting on the main? I have a 79 xs special thats just a nightmare opened up the carb and they were already @150. The idle jets are all torn up from screwdrivering. Have no idea what size they are the jets are so beat.
The plugs were clean with the 150 main jet. When I first got my xs750 the idol jet was stripped too. All I did was carefully put an easy put into the jet and then back it out.
I might be buying one of these. I really like the look of them. The one I'm getting has been in storage for a long time, but the engine turns. What's an easy way to sinc the carbs after I rebuild them?
An easy way to sync the carbs is when they are off the bike and on the bench. Basically you use the backside of a small drill bit and open the butterflys and use the drill bit as a gauge to make sure they are adjusted so they open and close the same. This will get you pretty close. Then to fine tune them you would have to use vacuum gauges while its running to ensure all the carbs suck the same. Have fun and good luck.
Also how is your gearing after the upjetting? I seem to only get about 10 miles before shifting? It gets better when i adjust the a/f mix screws? About 20 mph on the gauge til 2nd gear
im not sure I understand the question. The jetting will not change the gearing or change RPMs before you shift. The jetting only affects the way the engine runs.
@ what mph is 2nd, and 3rd gear for your xs? My 2nd gear is 20mph and 3rd gear is @ 30 mph... maybe clutch slippage?
So what did the plugs look like after the jetting
The plugs were clean. It was actually still a little lean at sea level.
@@Jeremybaland My problems. Im always lean no matter what I do with these mikunis and uni filters
@@jamesa6272 I had similar issues. The best you can do is put a big jet in, and use an air cleaner that isnt necessarily high flow.
@@Jeremybaland I would put the stock crap back on but I’m to much money into these mikunis. I have to restrict them
did you ensure float height was correct before altering your jets?
The float height was correct.
Hi can you tell me the torque settings on the head bolts please
The 8mm bolts are 14ft pounds 10mm are 25ft pounds. Camshaft cover nuts are 6-7 ft pounds. Camshaft cap nuts are 7 ft pounds.
you got the tape on the wrong end
Hi can not seem to find timing marks to set it up. And on timing chain there is a discoloured link. Has that anything to do with it
Stephen Wickenden I really really suggest you get a manual, it could be a lot cheaper. The discolored mark on the chain should have nothing to do with it. If the chain is placed on the cams correct all you should have to do is put number 1 cylinder TDC. You need to The " T " mark just right of the 1F mark needs to be aligned with the index mark. One way to double check is to pull the spark plug and put a plastic screwdriver in the number 1 cylinder head and rest it on the top of the piston, when its at the highest point you are at TDC.
Ok mate after all this just found out plugs in one engine are long reach and other engine short reach. Like 10 mil difference. But same amount of fins on both heads.
Hmmm I thought they were all the same. Someone probably put the wrong plugs in.
I am thinking perhaps one is 850 or 650
If its a triple I know its not a 650. The 650 is twin cylinder. They started making the 850 in 1980, you may be able to look up the VIN to find out. I don't think the difference should matter though with the spark plug.
what kind of carb is that, hitachi?
Where did you order your jets from? I have the same bike
I ordered them from jetsrus.com. good luck with it.
what size cone filter are those?
+Ruben Villarreal I have the same bike mine are 52mm
+Adam J thanks bro!
look up "Gunson colortune"
Well, you have a nice garage and set of tools, your only lack in knowledge, take it to a good mechanic, he' ll save you a lot of headecks, masking tape?, really?, who are you?, an Ichiban brother?, is good to try but you have to know when to give up "NEVER GIVE UP" not allways work, good luck!!
an ichiban brother? Really? that dudes an idiot. This guy right here took the time to correctly jet his bike for pods and free flow exhaust. The tape on the pods are no big deal im sure there are better things to use but the masking tape got the required job done
47.5 on the pilot fouls plugs after 1 week. dont go that fat. go 3 turns out on the mixture screw, and run a 43... stock jet size is 40 for the xs750
hi.i have a xs 400 1981.im finding it's running a little rich.fuel screws are 3.5 turns out.42.5 pilot and 140 main jet bike runs ok revs to 10000 revs no problem. but feel its not right .any ideas🤔thanks
ON MY 79 XS750 special im running 145main 43.5slo jets... got that
same 3 into1, and I'm running naked uni pods (black inners) mechanical
shutoff petcocks... the vacuum stocks are trash.