Need help

[EasyE]

I have just recently gotten a yamaha big bear 350 atv and I think the carburetor is a little off on its setting,bc it cuts out at full throttle and it makes a weird pluff kinda sound 3-4 seconds after I hit the kill switch to shut the atv off. I don't know why it's doing that so any help will be greatly appreciated.

[Mech]

The "whoomph" noise is the carb backfiring and trying to set fire to your air-filter. Check there's a flame proof mesh between the carb and air-filter.

The reason the carb backfires like that is because the mixture is too lean. I'd suggest trying adjusting the idle mixture and speed to cure that, but the high speed symptom sounds like the whole carb is running lean. You could check the carb is getting plenty of fuel right to it's fuel bowl by undoing the drain screw on the bottom of the carb and making sure fuel keeps running out even after the bowl has drained. Then check the carb breathers are clean and not crimped off or anything. Then, if it's getting plenty of fuel to the bowl but not revving right out, probably best to take the carb off and strip it entirely, clean and adjust it, and that should cure the problems.