I have a 2000 Honda Foreman 450S 4x4 4 wheeler. Ever since I have had this machine, and even the person who had it before me said that it has always backfired. I am not real intelligent when it comes to vehicle or for that matter ATV repairs. I have taken it apart before and put it back together, but what I can't figure out is what is causing this to happen. For the most part, when I am riding hard and I let off of the gas the backfire is really loud. It also happens nearly every time that I am riding around with my kids and I put the 4 wheeler up, it backfires when I turn off the engine. Does this happen a lot with these 4 wheelers, and is there a way of fixing the problem? I have asked several different people, including those at the Honda shops and the only thing they ever tell me is to bring it in and let them look at it so that they can bill me. I know there has to be something that I am not catching on to here and any help would be greatly appreciated.

Thank you and God Bless,

Cory

it is running rich on the fuel....Turn the gas needle in the carburator 1/4 turn in (pilot screw). If that doesn't help try change the clip position in you needle 1 clip up.

I actually believe it's running lean, and not rich. Lean jetting will always cause a backfire when the throttle is closed. With the colder weather, it's probably even worse. You're pilot jet controls the low speed and off-idle response, and main jet controls the mid-full throttle response. I'd be willing to bet you need to upsize both of them, but the main jet for sure. Most 4 strokes are jetted lean from the factory, even many of the newest racing bikes. Once you get the jetting fixed, it'll start easier and run better, too!

i agree it sounds like its lean put bigger jets on and see what happens is that doesnt wprk check your timing on that cauld also cause a problem

This happened to me also and what I did was I adjusted the carb idle screw to lower the idle. After, I adjusted the valves and I had my spark plug replaced. Luckily the backfiring didn't bother me anymore well at least until now. But my dad had a backfiring issue with his BMW X5 and sadly I am helpless with that. The BMW parts that seems to need immediate attention are the gearbox and traction control and I don't have the slightest idea if that could be a culprit with BMW backfiring issues.

If your on it hard when it backfires, it's going to be the jet needle or main jet. The jet needle controls 1/4-3/4 throttle and the main jet controls 3/4 and above throttle.