Whenever I start my ATV, it’ll idle without moving for about 10 seconds and then just randomly take off, it’s not going full speed but still, I adjusted the airflow on the carb when I got it because it was running really bad and backfiring but whenever I tighten the air flow screw, it just makes it go without giving it any gas, when I loosen it, it doesn’t go but runs like ****.

 

Clean the carb out and check you have no air leaks on the inlet manifold and the choke works properly. Not sure what you mean by "adjusted the airflow" for setting idle speed you set the throttle stop, either how far the carb slide falls on a slide carb, or the butterfly stop on CD carbs. If you can't get it to idle right with that, on a clean carb, you may have to alter the idle jet adjuster, but care is needed, not too much at a time and remember where you started.

 

I adjusted the air/fuel screw is what I meant, the little Phillips screw with the spring on it, I cleaned the carb and checked for any leaks but it’s still accelerating and backfiring, do you know why it could be backfiring also?

 

Backfiring can have many causes, mixture not set right, air leak at exhaust where it fits onto head, or timing out, valves or ignition, but ignition timing is normally "fixed" on ATVs.

 

If it is automatic gearbox, try to adjust clutch. Loose the nut, and unscrew until stops, and turn 1/8 - 1/4 clockwise, and then tight locking nut.