Idle is set to low,adjust it when it's up to temperature. Also,with those aftermarket pipes,it sounds like it's lean and needs jetted properly.the popping back through the exhaust indicates a lean condition.
Looks like it had a filter on it too. Hey Chris, take some plastic and cover half the filter. Run it and see if the popping goes away. Try 3/4 covering the filter also. If it gets better, the carbs are lean like others have said. Easy way to check is find out the stock jet sizes and see if they are still in there. Pipe and exhaust will need a large change in everything, including 2 sizes larger pilots. (Or more)
That's a really common problem with a lot of Harley's, on deceleration the exhaust pulls in fresh air and causes the backfire due to pressure. People change the exhaust and don't get the carb re-jetted or the Injection system Tuned for the new exhaust. Could also be caused by a leak somewhere in the exhaust system causing the backfire.
@@SHSPVR Could be. Either way, as I said, I believe the jetting is the problem. I said to get a new exhaust because I personally don't like loud exhaust anymore. When I was younger I did. Now it's just annoying and let's game wardens know where you're at.
Its running lean and needs to be re-jetted. That is why its back firing. It also looks like the headers got pretty hot near the engine another indication of running lean.
I would mess with the jetting. Seems lean. But, there's no shame in taking things to a professional when necessary. I'm a fairly good hobby mechanic but i occasionally run into stuff that i can't figure out and a professional is the best option.
For real, I would check the jetting on the carbs. If you can't see the jetting number on the them, just find the stock jetting size and swap them out. Plus you can get a whole jetting kit with different size for like 5 or 10 bucks.
@@Music46and2 it's probably got stock jetting running aftermarket exhaust. My buddy had the same bike with stock jetting and aftermarket exhaust it ran the same way
You idiot its either the stator or the voltage regulator when one of these components fail it causes pre-detination resulting in a backfire . do your research dude before you give up on a project #buildsnotprojects
I used to race one of these in GNCC"s many years ago and I had the same issue with mine. It came from the cheap idle adjustment cable on these things. It's the cable sticking out the right side (if you're sitting on it correctly), with the little black twisty knob on the end of it. Water gets in there and it corrodes it to where it just stops working. I wished there was an aftermarket option for this piece because it surely needed one. Btw, u have to have the rear brake pressed to shift the gears easily. These bikes were notorious for wearing out their rear brakes often to where the censor wouldn't pick up the brake being pressed to let the bike change gears. I know this is probably a year or so late but wanted to drop a line. Great vid
I 100% agree the amount of air out doesn't equal to the amount in with fuel its popping and farting stock cans or do cams and valves to match them sweet hmf s
Used to have one of these Kfx’s, they have lots of power and are lots of fun but also gave me lots of issues. When going and switching from reverse make sure your leg is pressing hard on the rear brake to allow smooth switching between reverse. Great vid
you can put shims on for low speed fuel and then richen the primary jets for quite a few steps when you havde the duals and k and n, both need more fuel to run right and you should not be driving it lean you will blow the piston if you keep reving it lean and drive it on the trails
It's called the venturi principle just how your carburetors work as air passes over the hole it creates a vacuum that sucks up fuel or any liquid for that matter great video by the way.
Awesome buy Chris. Found a list for jet sizes relative to running altitude for The KFX700. These are indications only and any mods will affect final sizes. Note the larger jet size in the rear carburetor. Minor adjustment to needle height can be done with shims under the the needle clip as far as I know. Read the plugs after a good run at normal operating temperature. 0- 1,600ft - 135f-140r 1,600- 4,900ft - 132f-138r 4,900- 8,200ft - 130f-135r 8,200-11,500ft - 128f-130r 11,500-14,800ft - 120f-125r After market exhausts usually need next size larger jets as a minimum. Those exhaust backfires are usually caused by exhaust leaks that let in outside air/oxygen that explode the un-burned fuel in the pipe. Good luck mate.
I am a long time viewer...love this channel and I am thrilled at the success you are having. You deserve it. I love your skills and abilities and your humility. Keep on keeping on!!!
V-twins are pretty good at cooking long spark plug caps. I’ve had a similar thing in the past. The bad cylinder would get too much fuel due to no Spark then randomly ignite and back fire. The caps can look real good but they have micro cracks in them that arc off into the cylinder head wall. If it does have long spark plug caps I’d whip them out and test them for arcing. :)
one possibility? thats an aftermarket muffler, possibly whole aftermarket exhaust, it may need jetted for that exhaust; May need slightly bigger main and pilot jet
I agree with Lucas below, lean conditions will cause backfire, plus the exhaust sounds either gutted or the baffles are removed. Either way, this causes a lean fuel condition, re-jetting or restricting the exhaust could help the backfire.
Backfiring in the carb: Lean/false air, if the manifolds has O rings, coat them in a bit of oil, and when its running, spray some brake cleaner to all of the mating surfaces, if the idle goes up, then its an air leak. Also check the sparkplugs to see what color they are, i had this same problem with my atv, it was an air leak, and i hear that is an air leak because the rpms arent going down that fast as they should.
It's running like a bike thats Otherwise STOCK, and some dummy put a free-flowing exhaust system on and never changed to bigger Pilot and Main JETS!!!!!! CHECK AND CHANGE THE JETS IN BOTH CARBS DUDE! Look it up online, and order a stage 1 or stage 3 (or both) jet kit for it and try one or the other till it runs perfect- bikes with stock tiny EPA-approved jets with airbox modes or exhaust mods ALWAYS run like this till you get them jetted correctly
The kfx700 has always been a decent quad when taken care of Rather Be welding will get it figured out Hopefully we can get together and Rip sometime I have a Yamaha Raptor 660r Yamaha Vmax 600 twin hybrid a Honda 300ex big bore stage 2 hot cam T4 Pro Circuit Exhaust a Yamaha Moto 4 350 a Polaris Trail Boss 325 with a Polaris Indy 400 twin a Suzuki Quadrunner 250 my son's 50cc ATV 2 buggys a utv side by side a offroad go kart and 6 Off-road mowers check out our channel
1. You have a habit rev..rev..rev..and chopping the throttle. That loads up the fuel in the intake and can create a small backfire. 2 Since it is running well enough to drive, just riding it around may clear up some of the issues. 3. I suggest adding some Chemtool carb cleaner in the fuel and ride it around. Great video as always. Love your channel.
in many vehicles carburetors, the choke usually opens an extra fuel channel, rather than throttling the air in the same way as in cars. An idle circuit blockage may most likely be to blame, but forced to say that air leakage also causes a similar problem. but were the rubber plugs in place and intact in the vacuum connections for the synchronization of the carbons? its can be jets, air filtter,or the position of the embossing chamber that metal may be bent and does not give fuel like it normally gives when it is in the right position.
@@Ohiocountryboy-se2cn lots of dirtbike/quad engines are loud. My crf450r always sounds like it's ready to self destruct at certain rpms. Especially when it's cold. There's nothing wrong with it though. Valves are good, timing chain tension is good, it's just loud.
Hi put a clean rag in your tank, blow the rag around in the fuel tank with air get all the fuel out, and the cab, being outside in the sun can dry the rubber values makes them stiff.?
You can’t call it finished until you clear up that lean condition. Checking plugs, jetting sizes, carb settings and even checking silencer baffling are all logical steps. Gotta get it right to call it finished. Best of luck.
About the only things I can think of that you haven't checked would be plug wires, coils and ignition control module. Coils can be ohm tested. Plug wires can be misted with water to see if insulation is breaking down. If all else fails you can try an ignition control module/cdi to see if it helps. The cdi module is not able to be tested so replacement is the only way to know. Coils can be intermittently bad even if they ohm out ok. Check for any bad connections or wiring between ignition components too. (Including at ignition switch) Fuel pump pressure ok? Good luck man, I am pulling for you.
Usually if you are running on choke you have a disconnected vacuum line or a vacuum leak. The carb and timing could also effect it. The gas typically just makes it sputter a lot. The backfiring makes me think timing, like the timing chain is off a tooth or two on the timing gear. Yes the airbox will effect it as the carb is tuned with that resistance. Usually on an older bike I would replace all the vacuum lines and gas lines as they are cheap. Then properly fix any janky wire reparse and mods people have done over the year. Clean all the plug connections and switches. Lube everything you can, including the cables and chain. I also replace the oil and filter, intake filters, and spark plugs. First though I typically pressure wash them. I typically run some carb cleaner through on a 1/4 tank of gas before I change the oil. It also sounds like they took the baffles out of the exhaust... which sometimes makes it run worse.
Alot of the people are correct in the comments... I was a motorcycle mechanic for 11 years... re-jet it for "stage 2" or 3 since it has the K&N and the exhaust... the are called afterfires not backfires... the gear shifting problem is either a bad adjustment (if cable) or electronic issue (if electric). Also for carb adjustment do not go off manual for air/fuel mixture screw ...start at 3 turns out from lightly seated and move 1/4 turn out until it makes no difference then back it off 1/2 turn
Id say the low speed idle mixture ports may be clogged up. I just went ham on my carbs and got the low speeds pristine with vinegar and a wire brush. The thing will idle at a seemingly 300rpm no more pops. Also changed out all the orings to with new viton seals. I did a jet kit and clean years ago it ran well but no where near what its like now.
If it smells fully at the pipes when running may be choke sticking a bit.. ground wire for coil pack/ maybe plug wire . Not shure but my problem is cured know. But I cleaned th he carbs also too. Hope it helps mine sounded like it was choking up like a hiccup sounded like vedic on starter sound almost low idle cutting out anyways best of luck. Sometimes a break is needed . An a cold one as well! looks amazing.
After jets… check the header nuts where it bolts to the head and make sure they are good and tight. Sometimes that can sound like lean pop if they are loose and exhaust is leaking out around the exhaust flange.
Oh my gosh! That is so wild that I did the very same thing yesterday with making a suction with a airhose into the side of a tube pointed the direction you want flow. And now I see you doing the same in a video. Its a very handy thing when you need it. I was sucking squirrel corn stash from breather tubes on a mustang that has been setting for a bit.
By the 1990s computer controlled ignition systems were becoming common and the need for more energetic spark generation with newer higher compression and forced induced engines was becoming apparent. This was accomplished by moving ignition coils into assemblies that sat directly above the spark plug. Known as coil-on-plug ignition, the one coil per cylinder configuration coupled with the shorter direct path of current flow allows for extremely high voltages to be used, often well past 100,000 volts. On modern fuel injected cars, higher compression ratios as well as tighter control of combustion timing is used to extract as much energy as possible, increasing power and efficiency. As an engine’s rotating speed increases, triggering an ignition event slightly before the point of maximum compression within a cylinder, or advancing timing is done to give the combustion process more time to occur. Under certain conditions uncontrolled combustion can be triggered as smalls pockets of air-fuel mixture explode outside the envelope of the normal spark triggered combustion front. This is known as detonation and it can occur when timing is advanced too aggressively or the air-fuel trim is mismatched for the conditions within the cylinder. Engine knock sensors were developed for this task and they functioned as highly tuned microphones, listening for the tones of sound produced on an engine block as it experiences detonation. The ability to accurately manage detonation also kept combustion chamber designs relatively conservative. During the late 1990's several manufacturers were researching better methods to detect detonation. The advent of ionic detonation detection used spark plugs to sense chamber ionization.
check torque on heads, or could need head gaskets. check spark plug gap and it gots the correct spark plugs in it, Premium gas will also make a change for the better. ignition coils could be funky, check them also i just noticed you did'nt mention any of these things. it could be any one of these because this seems to be an older model. Best of luck to you Chris, I have been a sub for a long time really enjoy your work and skills, thanks.
nice use of a Venturi to get the last bit of fuel out of the tank, i think some of the commenters here are on the right track, it sounds lean, either find a stock exhaust, or richen up the mix with slightly bigger jets
Check the rubber diaphragms in the top of the carbs for stiffness, rusted springs or corroded needle seats. The diaphragms may have pin holes in them and cause the low idle and backfiring.
I worked on a Kawasaki prairie a few year's back and after messing with that thing i found that there was a toggle switch inside the belt cover that had went bad causing it to have similar problems that your having
The seat cover would have looked better if you removed the original one first. Other than that, just run it and see if it will clear up. You get that sometimes with an engine that has been sitting for a while.
Because there is spark it doesn’t mean plugs are good. Breaks of conductive material inside of plugs will alter timing because more gaps to jump.Happened on a lawnmower with me. Changing a what looked to be a good plug with a new one fixed it.
i think before u give up on it rejet the carbs a couple sizes bigger its cheap enough to try .. that looks like a aftermarket exhaust usually that popping threw the intake is a lean running issue if it dont work your only out a few bucks ... give it a try or better yet call that exhaust company and see if they have a recommendation for jet size
"Timing is everything":Valve Lash,Valve Lash.2 Cyls.,and they aren't even.With the way you drive,(easy 90%)it's harder to diagnose,but I watch enough to hear the wrong.Great buy !
As many folks have said, you’re probably running lean. Plus, there’s a chance your carbs aren’t in sync. Which surprises me that you don’t have a sync gauge with as many motorcycle engines you use. Fix your jetting, readjust the idle, and check your carbs are in sync.
The cooling fan shouldn’t come on soon as you turn the key on. Mine has to run on choke a while before It runs good. It’s always been like that. I have an 06 with stage one hot cams and same dual exhaust with k&n air filter and re jetted carbs. It’s been an awesome 4 wheeler. Like others said, To put it in reverse you have to push down the rear brake first.
Thanks for making me spend 2 hours reading about Bernoulli’s principle and fluid dynamics lol! Seriously though, interesting read.. I’ve heard it in reference to carburetors before so I looked it up
If it was mine I would: 1. Change the exhausts back to stock. 2. Check the jetting to the factory specs and replace jets if needed. 3. Balance the carbs to get it running as smooth as possible. The carb balance makes so much difference to off idle smoothness yet lots of people never check it....
With that exhaust you likely need to re jet. Like a 46 pilot and I don't remember the main jet sizing, but one step over factory if it's stock otherwise. I have the same motor in a twin peaks, with cross over manifold, cdi, and a can... jetting changed A LOT... 1/8" drilled mains.
It's still lean. With aftermarket exhaust the main jet needs to be increased. Slow circuit may still have an obstruction. Adjust the cam chain and valve lash.
Check all of the carburetor diaphragms there’s two small ones on the side on each carb and the ones from the needle sides if they tear they run like crap and if they’re good just put a jet kit on it to compensate for that exhaust
Try checking the gasket between the carburetor and motor, if that sucking air it will do that . It happened to me on my .mine runs good now .its basically a vacuum leak.
Have you checked ignition coils could be a intermisive spark, sparks and then doesn’t the sparks again causing it to die fuel in the cylinder and in the exhaust
Pour some 500ml of brake fluid at both carburetors intake while holding acceleration at half maximum rpm. This old school recipe helps a lot on valve sealing by removing any unwanted material there. It makes a lot of white smoke but it works. Bad valve sealing may be the cause of back firing
its can be at poping comes from not correct adjust in starter clutch, so have you look at your starter clutch keyway have not broke and let move even little pit to set timing off.
I'd check the factory recommended cam lobe tolerance and see if the one in the motor is worn. With everything else done, I'd think there could be cam lobe wear. Easily this can cause the symptoms your motor is experiencing. Its easy to do too.
Gotta step on the brake pedal to go from reverse to fwd. there’s a lockout, that’s part of the reason it’s so difficult to shift.
Just wanted to say that
Idle is set to low,adjust it when it's up to temperature. Also,with those aftermarket pipes,it sounds like it's lean and needs jetted properly.the popping back through the exhaust indicates a lean condition.
I was thinking the same thing. it need jetted badly for his altitude and pipes.. Its def lean popping
Totally agree. Lean pop is evident.
Looks like it had a filter on it too. Hey Chris, take some plastic and cover half the filter. Run it and see if the popping goes away. Try 3/4 covering the filter also. If it gets better, the carbs are lean like others have said. Easy way to check is find out the stock jet sizes and see if they are still in there. Pipe and exhaust will need a large change in everything, including 2 sizes larger pilots. (Or more)
My thoughts exactly
That's a really common problem with a lot of Harley's, on deceleration the exhaust pulls in fresh air and causes the backfire due to pressure. People change the exhaust and don't get the carb re-jetted or the Injection system Tuned for the new exhaust. Could also be caused by a leak somewhere in the exhaust system causing the backfire.
Jets, jets, jets!!! Find a stock exhaust and rejet back to factory. Also, let some air out of those back tires. Great videos!
No more likely it wasn't jet with new exhaust
@@SHSPVR Could be. Either way, as I said, I believe the jetting is the problem. I said to get a new exhaust because I personally don't like loud exhaust anymore. When I was younger I did. Now it's just annoying and let's game wardens know where you're at.
@@denniscooper6328 that true
Yes I was going to say same thing or see what size jets you would need for that hmf exhaust
@@justinluce7773 It actually the pilot jet that cause this not the main jet just so you know
Its running lean and needs to be re-jetted. That is why its back firing. It also looks like the headers got pretty hot near the engine another indication of running lean.
The HMF exhaust requires carburetor re-jetting. I guess he doesn’t realize that.
That was my thought as well watching the vid. Running lean. Justin W is correct. After-market exhausts require exact jetting
Think he'd rather be welding than messing with fuel/air mixtures.
😂🤣
I would mess with the jetting. Seems lean. But, there's no shame in taking things to a professional when necessary. I'm a fairly good hobby mechanic but i occasionally run into stuff that i can't figure out and a professional is the best option.
That's what I was going to say lol
For real, I would check the jetting on the carbs. If you can't see the jetting number on the them, just find the stock jetting size and swap them out. Plus you can get a whole jetting kit with different size for like 5 or 10 bucks.
@@Music46and2 it's probably got stock jetting running aftermarket exhaust. My buddy had the same bike with stock jetting and aftermarket exhaust it ran the same way
That’s a great find for $800! My money would be on a sticky valve. Might improve with some run time.
You idiot its either the stator or the voltage regulator when one of these components fail it causes pre-detination resulting in a backfire . do your research dude before you give up on a project #buildsnotprojects
I used to race one of these in GNCC"s many years ago and I had the same issue with mine. It came from the cheap idle adjustment cable on these things. It's the cable sticking out the right side (if you're sitting on it correctly), with the little black twisty knob on the end of it. Water gets in there and it corrodes it to where it just stops working. I wished there was an aftermarket option for this piece because it surely needed one. Btw, u have to have the rear brake pressed to shift the gears easily. These bikes were notorious for wearing out their rear brakes often to where the censor wouldn't pick up the brake being pressed to let the bike change gears. I know this is probably a year or so late but wanted to drop a line. Great vid
I would put a stock exhaust back on it. It was probably not jetted for it anyways
I 100% agree the amount of air out doesn't equal to the amount in with fuel its popping and farting stock cans or do cams and valves to match them sweet hmf s
Even an adjustment on the air fuel screw would help
It's the Venturi effect. it's also used in carburetors to suck the gas into the air intake. You were kind of close with the name.
Came here to say the same
Me too 😂
Smarter everday' just did a video on it recently.
You realize the venturi effect is based on Bernoulli's principle?
@@gt1man931 That I didn't know. Also that makes him right then?
Backfiring like that could be the sign of running lean, which could possibly be caused by the aftermarket exhaust.
Used to have one of these Kfx’s, they have lots of power and are lots of fun but also gave me lots of issues. When going and switching from reverse make sure your leg is pressing hard on the rear brake to allow smooth switching between reverse. Great vid
Do those carburetors even have idle adjuster screws? Cuz the idle definitely sounds a little low
you can put shims on for low speed fuel and then richen the primary jets for quite a few steps when you havde the duals and k and n, both need more fuel to run right and you should not be driving it lean you will blow the piston if you keep reving it lean and drive it on the trails
It's called the venturi principle just how your carburetors work as air passes over the hole it creates a vacuum that sucks up fuel or any liquid for that matter great video by the way.
The carbs need to be jetted because it has that performance exhaust system on it
Idle needs to be turned up. There’s a black knob on the front fender foot well to turn it up
Awesome buy Chris.
Found a list for jet sizes relative to running altitude for The KFX700. These are indications only and any mods will affect final sizes. Note the larger jet size in the rear carburetor. Minor adjustment to needle height can be done with shims under the the needle clip as far as I know. Read the plugs after a good run at normal operating temperature.
0- 1,600ft - 135f-140r
1,600- 4,900ft - 132f-138r
4,900- 8,200ft - 130f-135r
8,200-11,500ft - 128f-130r
11,500-14,800ft - 120f-125r
After market exhausts usually need next size larger jets as a minimum.
Those exhaust backfires are usually caused by exhaust leaks that let in outside air/oxygen that explode the un-burned fuel in the pipe.
Good luck mate.
I am a long time viewer...love this channel and I am thrilled at the success you are having. You deserve it. I love your skills and abilities and your humility. Keep on keeping on!!!
V-twins are pretty good at cooking long spark plug caps. I’ve had a similar thing in the past. The bad cylinder would get too much fuel due to no Spark then randomly ignite and back fire. The caps can look real good but they have micro cracks in them that arc off into the cylinder head wall. If it does have long spark plug caps I’d whip them out and test them for arcing. :)
one possibility? thats an aftermarket muffler, possibly whole aftermarket exhaust, it may need jetted for that exhaust; May need slightly bigger main and pilot jet
My thoughts too. It may just be a tune issue.
This would be my guess also. High flow air filter and aftermarket exhaust requires jetting.
I agree with Lucas below, lean conditions will cause backfire, plus the exhaust sounds either gutted or the baffles are removed. Either way, this causes a lean fuel condition, re-jetting or restricting the exhaust could help the backfire.
Have you synced the carburetors? Try that, if it doesn’t work, adjust the pms screw or try some bigger jets.
I agree with the running lean aspect. One other thing I have run into is spark plugs. A partially fouled or cracked ceramic plug can give you fits.
Backfiring in the carb: Lean/false air, if the manifolds has O rings, coat them in a bit of oil, and when its running, spray some brake cleaner to all of the mating surfaces, if the idle goes up, then its an air leak. Also check the sparkplugs to see what color they are, i had this same problem with my atv, it was an air leak, and i hear that is an air leak because the rpms arent going down that fast as they should.
It's running like a bike thats Otherwise STOCK, and some dummy put a free-flowing exhaust system on and never changed to bigger Pilot and Main JETS!!!!!!
CHECK AND CHANGE THE JETS IN BOTH CARBS DUDE! Look it up online, and order a stage 1 or stage 3 (or both) jet kit for it and try one or the other till it runs perfect- bikes with stock tiny EPA-approved jets with airbox modes or exhaust mods ALWAYS run like this till you get them jetted correctly
You have a nice four wheeler I hope you get it figured out and have a lot of fun with it
The 700s are insane my friend use to have one an it was freaking sick it pulled really hard. They did have a decent amount of electrical issues tho.
The kfx700 has always been a decent quad when taken care of Rather Be welding will get it figured out Hopefully we can get together and Rip sometime I have a Yamaha Raptor 660r Yamaha Vmax 600 twin hybrid a Honda 300ex big bore stage 2 hot cam T4 Pro Circuit Exhaust a Yamaha Moto 4 350 a Polaris Trail Boss 325 with a Polaris Indy 400 twin a Suzuki Quadrunner 250 my son's 50cc ATV 2 buggys a utv side by side a offroad go kart and 6 Off-road mowers check out our channel
@@phoenixarizona8441 dam bro. Im coming to hang out with you. Lol
1. You have a habit rev..rev..rev..and chopping the throttle. That loads up the fuel in the intake and can create a small backfire. 2 Since it is running well enough to drive, just riding it around may clear up some of the issues. 3. I suggest adding some Chemtool carb cleaner in the fuel and ride it around. Great video as always. Love your channel.
in many vehicles carburetors, the choke usually opens an extra fuel channel, rather than throttling the air in the same way as in cars. An idle circuit blockage may most likely be to blame, but forced to say that air leakage also causes a similar problem. but were the rubber plugs in place and intact in the vacuum connections for the synchronization of the carbons? its can be jets, air filtter,or the position of the embossing chamber that metal may be bent and does not give fuel like it normally gives when it is in the right position.
They are a beast of a quad my brother owned one for some time and they have so much torque
Sounds like the valves might be sticking or may need to be adjusted to spec. That aftermarket pipe sounds crappy.
He said he checked the lash. Could be sticking though.
Kawasaki always makes valve noise. I bought one new and they said its normal.
@@Ohiocountryboy-se2cn lots of dirtbike/quad engines are loud. My crf450r always sounds like it's ready to self destruct at certain rpms. Especially when it's cold. There's nothing wrong with it though. Valves are good, timing chain tension is good, it's just loud.
lean condition, re jet it or you will hurt it,love your projects but spend some time learning about tuning and how to check the spark plugs
Hi put a clean rag in your tank, blow the rag around in the fuel tank with air get all the fuel out, and the cab, being outside in the sun can dry the rubber values makes them stiff.?
You can’t call it finished until you clear up that lean condition. Checking plugs, jetting sizes, carb settings and even checking silencer baffling are all logical steps. Gotta get it right to call it finished. Best of luck.
About the only things I can think of that you haven't checked would be plug wires, coils and ignition control module. Coils can be ohm tested. Plug wires can be misted with water to see if insulation is breaking down. If all else fails you can try an ignition control module/cdi to see if it helps. The cdi module is not able to be tested so replacement is the only way to know. Coils can be intermittently bad even if they ohm out ok. Check for any bad connections or wiring between ignition components too. (Including at ignition switch) Fuel pump pressure ok? Good luck man, I am pulling for you.
100% needs re jetted. Either put a stock exhaust on it, or jet it correctly for that exhaust.
Usually if you are running on choke you have a disconnected vacuum line or a vacuum leak. The carb and timing could also effect it. The gas typically just makes it sputter a lot. The backfiring makes me think timing, like the timing chain is off a tooth or two on the timing gear. Yes the airbox will effect it as the carb is tuned with that resistance. Usually on an older bike I would replace all the vacuum lines and gas lines as they are cheap. Then properly fix any janky wire reparse and mods people have done over the year. Clean all the plug connections and switches. Lube everything you can, including the cables and chain. I also replace the oil and filter, intake filters, and spark plugs. First though I typically pressure wash them. I typically run some carb cleaner through on a 1/4 tank of gas before I change the oil. It also sounds like they took the baffles out of the exhaust... which sometimes makes it run worse.
I had a kfx 400 that the stater went bad. It was running like that. It’s a $800 computer though so hopefully it’s not that.
Sticky valves bud ad some valve ease in the feul and let it run for a bit
Alot of the people are correct in the comments... I was a motorcycle mechanic for 11 years... re-jet it for "stage 2" or 3 since it has the K&N and the exhaust... the are called afterfires not backfires... the gear shifting problem is either a bad adjustment (if cable) or electronic issue (if electric). Also for carb adjustment do not go off manual for air/fuel mixture screw ...start at 3 turns out from lightly seated and move 1/4 turn out until it makes no difference then back it off 1/2 turn
Leak down test of possible. Sounds like valves might now seat right and needs clutches cleaned and new belt would be a plus
Put some seafoam in your gas tank and a bit in the oil, also it has aftermarket exhaust, try rejetting it.
Id say the low speed idle mixture ports may be clogged up. I just went ham on my carbs and got the low speeds pristine with vinegar and a wire brush. The thing will idle at a seemingly 300rpm no more pops. Also changed out all the orings to with new viton seals. I did a jet kit and clean years ago it ran well but no where near what its like now.
If it smells fully at the pipes when running may be choke sticking a bit.. ground wire for coil pack/ maybe plug wire . Not shure but my problem is cured know. But I cleaned th he carbs also too. Hope it helps mine sounded like it was choking up like a hiccup sounded like vedic on starter sound almost low idle cutting out anyways best of luck. Sometimes a break is needed . An a cold one as well! looks amazing.
After jets… check the header nuts where it bolts to the head and make sure they are good and tight. Sometimes that can sound like lean pop if they are loose and exhaust is leaking out around the exhaust flange.
The air method you used is the exact way old school centerpoint injection works. Kinda cool if you ask me
Oh my gosh! That is so wild that I did the very same thing yesterday with making a suction with a airhose into the side of a tube pointed the direction you want flow. And now I see you doing the same in a video. Its a very handy thing when you need it. I was sucking squirrel corn stash from breather tubes on a mustang that has been setting for a bit.
By the 1990s computer controlled ignition systems were becoming common and the need for more energetic spark generation with newer higher compression and forced induced engines was becoming apparent. This was accomplished by moving ignition coils into assemblies that sat directly above the spark plug. Known as coil-on-plug ignition, the one coil per cylinder configuration coupled with the shorter direct path of current flow allows for extremely high voltages to be used, often well past 100,000 volts.
On modern fuel injected cars, higher compression ratios as well as tighter control of combustion timing is used to extract as much energy as possible, increasing power and efficiency. As an engine’s rotating speed increases, triggering an ignition event slightly before the point of maximum compression within a cylinder, or advancing timing is done to give the combustion process more time to occur.
Under certain conditions uncontrolled combustion can be triggered as smalls pockets of air-fuel mixture explode outside the envelope of the normal spark triggered combustion front. This is known as detonation and it can occur when timing is advanced too aggressively or the air-fuel trim is mismatched for the conditions within the cylinder.
Engine knock sensors were developed for this task and they functioned as highly tuned microphones, listening for the tones of sound produced on an engine block as it experiences detonation. The ability to accurately manage detonation also kept combustion chamber designs relatively conservative. During the late 1990's several manufacturers were researching better methods to detect detonation. The advent of ionic detonation detection used spark plugs to sense chamber ionization.
Good . Th
it is ok
check torque on heads, or could need head gaskets. check spark plug gap and it gots the correct spark plugs in it, Premium gas will also make a change for the better. ignition coils could be funky, check them also i just noticed you did'nt mention any of these things. it could be any one of these because this seems to be an older model. Best of luck to you Chris, I have been a sub for a long time really enjoy your work and skills, thanks.
nice use of a Venturi to get the last bit of fuel out of the tank, i think some of the commenters here are on the right track, it sounds lean, either find a stock exhaust, or richen up the mix with slightly bigger jets
Check the rubber diaphragms in the top of the carbs for stiffness, rusted springs or corroded needle seats. The diaphragms may have pin holes in them and cause the low idle and backfiring.
Chris, you can tune that bog/backfire out of it. Adjust the a/f mixture screws.
The cdi or ignition. It's whatever makes the spark plugs fire
I worked on a Kawasaki prairie a few year's back and after messing with that thing i found that there was a toggle switch inside the belt cover that had went bad causing it to have similar problems that your having
You have to do a cylinder leakage test suspect intake valve leak
The seat cover would have looked better if you removed the original one first. Other than that, just run it and see if it will clear up. You get that sometimes with an engine that has been sitting for a while.
Because there is spark it doesn’t mean plugs are good. Breaks of conductive material inside of plugs will alter timing because more gaps to jump.Happened on a lawnmower with me. Changing a what looked to be a good plug with a new one fixed it.
i think before u give up on it rejet the carbs a couple sizes bigger its cheap enough to try .. that looks like a aftermarket exhaust usually that popping threw the intake is a lean running issue if it dont work your only out a few bucks ... give it a try or better yet call that exhaust company and see if they have a recommendation for jet size
"Timing is everything":Valve Lash,Valve Lash.2 Cyls.,and they aren't even.With the way you drive,(easy 90%)it's harder to diagnose,but I watch enough to hear the wrong.Great buy !
As many folks have said, you’re probably running lean. Plus, there’s a chance your carbs aren’t in sync. Which surprises me that you don’t have a sync gauge with as many motorcycle engines you use. Fix your jetting, readjust the idle, and check your carbs are in sync.
Great vid. keep up the good work Chris.
Chris had you would've cleaned those carbs and tank in last video we wouldn't have got this great video, awesome work!
Keep putting it in reverse like that you'll be putting a transmission in it its also running lean
Wonder if they rejetted the carbs properly when the HMF exhaust was installed?
Finally... Nice work buddy 😉
The cooling fan shouldn’t come on soon as you turn the key on. Mine has to run on choke a while before It runs good. It’s always been like that. I have an 06 with stage one hot cams and same dual exhaust with k&n air filter and re jetted carbs. It’s been an awesome 4 wheeler. Like others said, To put it in reverse you have to push down the rear brake first.
Spark plugs and timing then check ignition components...
Check your valve lash and coolant temperature sensor would be my first look, In coolant temp center helps regulate the fuel intake on an engine
Call hmf and get the right jets . Maybe check the air screw settings too.
I would check the mixture screws with it blowing that little bit of smoke on acceleration looks like it's running a bit rich
Had a Polaris scrambler 500 do that, turned out to be the cam was worn. Not saying that's it but the symptoms are similar
Make sure the carbs are balanced in. Both pulling same amount of vacuum
Thanks for making me spend 2 hours reading about Bernoulli’s principle and fluid dynamics lol! Seriously though, interesting read.. I’ve heard it in reference to carburetors before so I looked it up
It sounds to be idling low. Also with the aftermarket pipes the jetting has to be spot on. When the motor is decelerating it will pop like yours is.
Check for vacuum ports on the carbs that may be open, and block them off.
if you haven't done it I would suggest syncing the carbs or checking the fuel pressure
Jetting like much others have said. But I've owned a few of these make sure those carbs are synced and valves lashed correctly
If it was mine I would:
1. Change the exhausts back to stock.
2. Check the jetting to the factory specs and replace jets if needed.
3. Balance the carbs to get it running as smooth as possible. The carb balance makes so much difference to off idle smoothness yet lots of people never check it....
How do I adjust my carb on mine I can’t find the screw
Yeah back to the projects!
not sure but my sportsman 500 was acting the same as well as hard starting, come to find out the flywheel key way was sherd off affecting the timing
It’s green so it’s nature, great vids!!
Good job on the seat cover.
With that exhaust you likely need to re jet. Like a 46 pilot and I don't remember the main jet sizing, but one step over factory if it's stock otherwise. I have the same motor in a twin peaks, with cross over manifold, cdi, and a can... jetting changed A LOT... 1/8" drilled mains.
If it backfiring into the intake, it can only be one thing sticky valves. if you run it a while they will probably free up.
It's still lean. With aftermarket exhaust the main jet needs to be increased. Slow circuit may still have an obstruction. Adjust the cam chain and valve lash.
Check all of the carburetor diaphragms there’s two small ones on the side on each carb and the ones from the needle sides if they tear they run like crap and if they’re good just put a jet kit on it to compensate for that exhaust
I had the same problem with my yamaha raptor 350. I had to replace the pickup coil and after that it was running perfectly.
Have you check the air fuel mixture screw? May it needs a tune up, not because you clean the carburetor means it's ok
My guess is they installed the aftermarket exhaust and it's running really lean
Hmf recommends 142 front jet and 145 rear jet in the exhaust manual
HMF usually has the recommended jet sizes and carb adjustments to use with there pipes on the website.
Try checking the gasket between the carburetor and motor, if that sucking air it will do that . It happened to me on my .mine runs good now .its basically a vacuum leak.
when you go from reverse to neutral you need to use the back brakes
Have you checked ignition coils could be a intermisive spark, sparks and then doesn’t the sparks again causing it to die fuel in the cylinder and in the exhaust
and when you sell it, say "i inherited it and didn't do anything to it"
Backfiring in the intake is only one thing that causes that intake valve is hanging open or bent or burnt Valves
Check the jets sizes and see if they are stock. If they are install a aftermarket jet kit. Like Dynojet. Sounds lean.
I cant wait to see your dream shop build. I know it's only a matter of time.
He needs a 40x60 at least.
He really needs some property away from shitty neighbors, then build the shop there.
Pour some 500ml of brake fluid at both carburetors intake while holding acceleration at half maximum rpm. This old school recipe helps a lot on valve sealing by removing any unwanted material there. It makes a lot of white smoke but it works. Bad valve sealing may be the cause of back firing
its can be at poping comes from not correct adjust in starter clutch, so have you look at your starter clutch keyway have not broke and let move even little pit to set timing off.
I'd check the factory recommended cam lobe tolerance and see if the one in the motor is worn. With everything else done, I'd think there could be cam lobe wear. Easily this can cause the symptoms your motor is experiencing. Its easy to do too.