banshee 268 Posted March 14, 2010 Report Share Posted March 14, 2010 ok i have a right cylinder back fire at low rpm and only idles on one cylinder.when i pull the choke out it runs on both cylinders and the back fire goes away.so i took it apart and found a pin hole in the cross over tube betweenthe carbs.so i covered the hole up and started it and it still seemed to have a back fire.i checked both carb boots and there perfect.all the gaskets are good,this was the only thing i could find.the carbs have 250 mains and 25 piolet.the bike is all stock except for the exhaust.full fmf gnarly pipe.its also around 50 deg.at sea level.any help would be great.thanks for ur time Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted March 14, 2010 Report Share Posted March 14, 2010 ok i have a right cylinder back fire at low rpm and only idles on one cylinder.when i pull the choke out it runs on both cylinders and the back fire goes away.so i took it apart and found a pin hole in the cross over tube betweenthe carbs.so i covered the hole up and started it and it still seemed to have a back fire.i checked both carb boots and there perfect.all the gaskets are good,this was the only thing i could find.the carbs have 250 mains and 25 piolet.the bike is all stock except for the exhaust.full fmf gnarly pipe.its also around 50 deg.at sea level.any help would be great.thanks for ur time has it always run like this....or did you just pick up the bike? Did you put the fmf's on? your gonna have to fix that choke tube...that'll lean you out. and also you may need to step up your pilot jet from the stock size (25) to a 27.5 Sounds like something my bike was doin when i first bought it.....fmf fattys...idled bad and popped and had no bottom end when in gear but it would rev in neutral just fine. Tore the carb jetts out and put in the 27.5....wow did it change alot. Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 14, 2010 Author Report Share Posted March 14, 2010 has it always run like this....or did you just pick up the bike? Did you put the fmf's on? your gonna have to fix that choke tube...that'll lean you out. and also you may need to step up your pilot jet from the stock size (25) to a 27.5 Sounds like something my bike was doin when i first bought it.....fmf fattys...idled bad and popped and had no bottom end when in gear but it would rev in neutral just fine. Tore the carb jetts out and put in the 27.5....wow did it change alot. i just got the bike and its run like this from the day i got it.the choke tube has a good connection.i also just checked and im 489 feet above sea level Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted March 14, 2010 Report Share Posted March 14, 2010 I'm not saying you don't have a jetting issue, but I think the root of your problem sounds like carb sync. Also check that you have a good connection between you spark plugs and plug caps. You can switch the plug wires and see if the problem moves to the other cylinder to rule out electrical issues. Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 14, 2010 Author Report Share Posted March 14, 2010 I'm not saying you don't have a jetting issue, but I think the root of your problem sounds like carb sync. Also check that you have a good connection between you spark plugs and plug caps. You can switch the plug wires and see if the problem moves to the other cylinder to rule out electrical issues. k did the plug wire thing and it stays at the right cylinder.i even put new plugs in it.pulled the right wire while running and it didnt make a difference.pulled the left one and it shut down.so it acts like its not getting gas for some reason Quote Link to comment Share on other sites More sharing options...
wacko2000 Posted March 14, 2010 Report Share Posted March 14, 2010 Have you taken you carbs apart yet and cleaned the shit out of them?? They could be dirty inside.. You should have a leak down test done, I had a problem simaliar to yours and it was a air leak and I ended up frying the motor in glamis. I would do a leak down and compression test and than go from there before you hurt the motor. Just my opinion Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 14, 2010 Author Report Share Posted March 14, 2010 Have you taken you carbs apart yet and cleaned the shit out of them?? They could be dirty inside.. You should have a leak down test done, I had a problem simaliar to yours and it was a air leak and I ended up frying the motor in glamis. I would do a leak down and compression test and than go from there before you hurt the motor. Just my opinion k thanks will do.i have done the carbs a couple times thinking there was stuff coming from the tank but was very clean in carbs every time.ill do leak down test and check compression Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 15, 2010 Author Report Share Posted March 15, 2010 k thanks will do.i have done the carbs a couple times thinking there was stuff coming from the tank but was very clean in carbs every time.ill do leak down test and check compression k well so far ive done a leak down test and it held 6lbs for 30 min with no loss.now i gotta get a compression tester to do the test.what should stock have for compression Quote Link to comment Share on other sites More sharing options...
lykins89shee Posted March 16, 2010 Report Share Posted March 16, 2010 Around 120 Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 16, 2010 Author Report Share Posted March 16, 2010 Around 120 k i just did a compression test and both cylinders have 100 psi exact Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted March 17, 2010 Report Share Posted March 17, 2010 k i just did a compression test and both cylinders have 100 psi exact have you pulled the carbs apart to clean them out? and have you tried the 27.5 jets yet? they're not expensive....they're like $3 a piece X 2....so $6 total Quote Link to comment Share on other sites More sharing options...
banshee 268 Posted March 18, 2010 Author Report Share Posted March 18, 2010 have you pulled the carbs apart to clean them out? and have you tried the 27.5 jets yet? they're not expensive....they're like $3 a piece X 2....so $6 total ya ive cleaned the carbs many times now.i did both test to it also.leak down and compression.it passed the leak down with no problems and the compression test was 100 psi in both.im still not seeing the problem.where can i buy the 27.5 piolet jets.i did order a jet kit for it.it has 250 mains right now and the only mods are the fmf pipes and box lid Quote Link to comment Share on other sites More sharing options...
Husemoller Posted March 26, 2010 Report Share Posted March 26, 2010 from what i have read around here i think 100 for the compression test is a little low but i have also heard that you really should make sure you have a good compression tester or it could very well read much lower psi then it really is Quote Link to comment Share on other sites More sharing options...
esterelbanshee Posted March 27, 2010 Report Share Posted March 27, 2010 It seems to me that 250 mains isn't nearly enough jetting for FMF's and no airbox lid. The lack of an airbox lid would require 230-240 jets alone never mind the pipes. Quote Link to comment Share on other sites More sharing options...
fastbanshee8 Posted March 27, 2010 Report Share Posted March 27, 2010 With FMF pipes, you should be between 270's, and 290's on your main jets. Pull the pilot jet out of the right carb, and spray some carb cleaner through it, then reinstall it. Quote Link to comment Share on other sites More sharing options...
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