Backfiring?

[blasterkiller14]

Could my bike be backfiring because its not jetted correctly?

[Chicksdigme423]

definetly, if you have it too rich it will definetly back fire... are you going through spark plugs? try leaning it out a little

[Punk'd]

Originally posted by blasterkiller14
Could my bike be backfiring because its not jetted correctly?

Your jettings off.

[bwamos]

When is it backfiring.. when you're letting off of the gas?

If so try turning your Air Screw out a quarter to half turn.

[tater_kamik]

best way to tell is by your plug, take it out and see what color it is. also, make sure you do not have an exhaust leak

[bwamos]

A plug reading won't show what causes the backfire.

Generally a backfire happens when you go from full throttle to no throttle causing an artficialy rich condition for a couple seconds. The backfire happens when it's just a little too rich.

Opening up the air screw a little will help add some air, and allow it to be a little less rich on deceleration. There's now way I know of to get a plug reading for deceleration.

Now, if he's getting a backfire while at a consistent full throttle, his jetting is way out of whack, he has an exhaust leak, or his timing is off.

[400exrules]

take your lid off, and if it runs better then your probably alittle rich.

[tater_kamik]

for one, we need to know when it backfires.
if it is at a high rpm and the throttle is closed, that is caused by the a/f mix becoming extremely lean and the engine is rotating much higher than idle, this is pretty normal when you have a very free flowing exhaust but does not mean anything is wrong.
why is this normal? well... at idle, fuel doesnt flow out of the needle, needle jet, main jet, only by the pilot jet. now when you have both the throttle closed, and a high engine rpm, there is a strong vacuum created in the intake manifold causing air to flow at a much higher rate through the carb and the throttle valve, causing the idle jet to not be able to deliver enough fuel. so little fuel that the a/f ratio it creates is not readily combustible and unburnt fuel ends up in the exhaust, then when it does fire, it will occasionally ignite the mixture that is in the exhaust causing a backfire. but backfiring is also caused by exhaust leaks, normally any of the junctions where the exhaust is not solid, but this can be fixed by using a high temp silicone. also, it can be caused by your ignition, but if this is the cause, the backfiring will probably be extremely loud, and random. you may also have a loss of power. this can be caused by components failing such as your plug, coil, etc.

[blasterkiller14]

It only does it when i have the throttle 3/4-full and then let off, or if im slowing down and drop it into a lower gear(or down hills). Its pretty annoying and does it alot.

[COLO400EX]

how long have you been running this handmade 2" headpipe. my buddy cut the last 3" off of his stock pipe in order to avoid buying a real exhaust. it backfired constantly(not enough backpressure) going down hills, downshifting, or even just letting off of the throttle. the CURE was locating another pipe (not handmade) this may not be your problem but i had to write because it WAS very annoying and we did fix it. an exhaust leak, upfront, could also be the prob. thanks