back firing

[yzf250rider]

hey guys, i know this would have already been gorne threw but anways here is the question, i have a 155/160 pitster pro and its backfiring and popping flames its fine revving and riding its just when your off the gas, its all brand new and was running sweet for the first week and now all of a sudden its popping crap, thanks dan

 

[Carlts]

Couple of reasons man, most common is its either running lean or there is an air leak between the engine and exhaust. Make sure the bike has an exhaust gasket and that it is also well tightened...

 

[yzf250rider]

ok thanks with the mixture screw do i turn it in out out if its lean? and ill check the leak now

 

[Carlts]

turning the mixture screw will only affect the leanness/richness of the idle. If you want to richen through all ranges, move the carby needle up one position, test it and move again if necessary. Also with the mixture screw try in he range of about 1 - 2 turns out, adjust it till the bike revs best....

 

[yzf250rider]

ok thanks mate

 

[DHZ_XR8cing]

yeh I would say your 2 exhaust bolts are lose on your head without a doubt

 

[yzf250rider]

yea i havnt ill have a check in the morning and let yous know how i go

 

[sean01]

the back firing/popping is pretty normal.. can be as simple the muffler slip join not sealing or the exhaust gasket in the head loose or damaged

 

[hiro]

There are a few other things that will cause back firing / popping
1 as stated exhaust gasket leak or poor muffler seal joint
2 leaking inlet manifold around the head or carby (vacuum leak)
3 is the worst case scenario is a burnt out valve this will also cause low compression

Cheers hiro

 

[yzf250rider]

it is not as bad anymore and it doesnt have all that much compression, i hope its not the valve :/ the motor is only probley 3 hours old, it has a fair bit when its cold but not much when its warm

 

[Carlts]

^^^ Unless your engine is running hopeless, feels sick or is hotter than a kid with fever, than I wouldn't worry a whole lot about it. My bike still does it to some degree, especially when backing off the revs...

 

[yzf250rider]

yea just double checking as i dont want to ruin my motor, thanks guys!

 

[Cactus Jack]

Check your valve clearances ... New valves wear in and lose clearance (causing valves to be held off their seats) which can cause a host of symptoms ie loss of compression , reversion thru the intake tract (Mist or spitting out of the carb , rich running) , popping , back firing etc ...

Back firing is the result of unburnt charge igniting and exploding in the pipe ... If a charge doesn't burn properly due to low compression it ends up in the pipe where it gets ignited on the next exhaust stroke ... A misfiring plug or ignition can also cause back firing ...

 

[yzf250rider]

cheers ill just get a bike shop to check everything and give it a tune when i got some more money

 

[naked racer]

hey mate did you find out what was wrong with it mine is popping and backfiring when i hold the revs at half throttle and it dies if i go any further then that

 

[Carlts]

^^^ Sounds like it could well be an air leak mate?

 

[naked racer]

checked for air leaks but i dont think its that because all the seals/gaskets are good and everything is tight i have been playing with the slide needle and it runs best on the very top setting but it still wont let me use more then half throttle (pops and backfires) if i put it on the second from the top setting it looses even more throttle

could it be the float level? it is a second hand motor so i dont know if the previous owner messed with that or not

 

[yzf250rider]

um i think i had to move the needle up a clip

 

[naked racer]

um i think i had to move the needle up a clip

dam i wish my problem was that simple i think i might have to let a shop figure it out because i dont have any spare parts i can use to test anything

 

[naked racer]

anyone know the valve clearance for 125 zongshen?