My quad is back firing once in awile when I let of throtle(only when riding)also when I let the engine hold me back on hill's...Could this be air feul mix or valve clearance?

 

Could be that you are running too lean. Check your elevation and your jetting.

 

pilot too lean

 

If your backfiring on deceleration then you need to adjust your air fuel screw out a 1/4 turn at a time until it stops. If you get your air/fuel screw out 4 turns then your pilot jet is to small. I doubt this is the case unless your jets have been changed.

 

Thanks I will try that... Does anyone know the factory setting for the air-fuel mix?

 

I don't know the factory settings but I would start at 1 1/2 turns out. Then go up in increments of a 1/4 turn at a time. Its probably just a little off. If you just go up from where it is now I'd bet you would get it on the first or second try.

 

It Could be valve clearance are off spec. , water and or trash in fuel ; or as others have stated improper air/fuel mixture . For the latter a simple spark plug check would be in order , if you're running lean plug electrode will be black , lean electrode color white ; for correct mixture electrode should be a brownish tan color ! I keep my tank full all the time summer and winter , and i also add seafoam to every tankfull to help keep water out ; the seafoam is a fuel cleaner/stabilizer that helps keep the entire fuel system clean ; and also cleans the combustion chamber of excessive carbon buildup around valves and the combustion chamber ! You can get the seafoam at O'Reallys, auto zone and advance auto parts stores , i get mine at O'Reallys for $4.99 + Tax ; price will vary according to your location ! Hope this help's........................williebee

 

How much is your Seafoam stock worth? Just kidding,good stuff.

 

If you hit the kill switch when you are going almost full throttle, and it backfires? what is the cause of that? i let a 6 year old drive my quad once in a flat field where you can just go wide open for a few minutes straight. Well he started approaching the road and wouldn't budge his thumb, so i just hit the kill switch and BAM!! it was the loudest bang ever, louder than 40 450s at the holeshot in motocross. is that bad?


When i got first got my quad, it backfired a lot, but after a while it just stopped. Problem should go away after a while.

 

The backfire is just unburned fuel , burning outside the combustion chamber. Even though the engine was off, the piston was still moving air and fuel, and it shoved it in the exhaust, where the hot pipe ignited it. Thats normal.
Back fire on let off, is cause by lean mixtures. Its a very fine line, between correct mixtures and lean. On my kodiak if i use pure gas, it wont back fire on letoff, but if i use any gas with alcohol, like 10% ethinol, itll back fire. Even a small adjustment of 1/4 turn on the mixture screw should fix it right up.