i have an 07 wolvy and after maybe 10 min of riding it backfires. i think well maybe im just running it too hard so i ease it down a little but then 5 min later it backfires again and im not even running it hard. and it will end up backfiring every 5 min or so and its usually when im slowing down. can anyone help? am i doing something wrong?

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2007 yamaha wolverine 450
2004 yamaha blaster

 

Mine has backfired 2 times now... Hmmm

 

The idle circuit is too lean. Try opening up the mixture screw by a 1/4 turn, and it should disapear.

 

ok thanks. hondabuster could you tell me where the mixture screw is? thanks


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2007 yamaha wolverine 450
2004 yamaha blaster

 

If you have your owners manual you can always find it in there. Maybe someone knows from the top of their head

 

Its on the underside of the carb, just in front of the float bowl. Its gonna probably have a metal or plastic plug over it, which will need to be drilled and pried out of there.

 

okay thank you

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2007 yamaha wolverine 450
2004 yamaha blaster

 

There are other things it could be. I find that winter blended gas is more volitile and has more alcohol in it, than summer blends. I can get my 450 to backfire just by using ethenol gasoline. So first thing to try, is use pure gas....no added alcohol, and see if the back fire goes away.
I probably should have given a more complete answer, so heres the answer, right off the Mikuni carb website

4: Backfires in Exhaust

Note:

It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.



Other possible causes:

Air Leaks:

Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust backfiring. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system backfiring.

A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction.

Lean Carburetion:

While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit.

Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping. The procedure for adjusting the pilot circuit is covered in the Tuning Manual.

Ignition:

If exhaust system popping is very loud, irregular and accompanied by loss of power, then you should suspect that the ignition system is not performing as it should. If, for some reason, the ignition sometimes fires at the wrong time, then exhaust popping can become very energetic (loud). Look for failing high tension leads (plug wires), failing ignition coil(s) and especially switches or connectors as possible causes.

If using pure gas doesnt cure it, it may go away when the temperatures warm up, because warmer air doesnt require the mixtures as rich as cold weather settings.

 

ok thanks that help alot

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2007 yamaha wolverine 450
2004 yamaha blaster