I just finished restoring an 83 atc 200, it ran perfict the first day on a 4 min run, the second day when I pull started it, it reved up real high and would only idle at a close to norm rpm with the choke fully on. When the choke is turned to the half on location the rpms jumps up to about half throttle, and when the choke is turned off, it raps out to full rpm with out any contact with the thumb throttle? what would cause this? an air leak? it has a real crappy airfilter that is about as restrictive as running no firter at all, that is being replaced with a uni filter and I just ordered a carb rebuild kit. also the air/fuel mix screw can be fully turned "in" when the motor is running and the motor will keep running. I have adjusted the needle setting in the carb to be in the fully down position so it should not be allowing much fuel to pass at idle, but it just raps out when started. Please help

 

Is the slide sticking in the Carb
That can cause a bad day
You could also have a crack in the intake
I believe they are a vulcanized rubber
Same as a 185S
Is the thumb throttle lever seem loose
Or even easier Pull carb leave slude in look in carb and work throttle should move freely
Good luck
Ray

 

if it has a needle carb the needle might need adjustment

 

Not being able to change anything with the mixture screw, means the slide is up, and the motor is running on the needle circuit instead of the idle circuit.
Youve got to figure out why the slide stays open. throttle cable routed wrong, throttle cable kinked or rusty, slide is in backwards, needle is bent, idle speed screw too far in....and so on.
Then make sure you check the pilot (idle) jet. Its probably plugged shut

 

try seafoam ii had the same problom with my 185s u can it at advanced autoparts
for $7 it is worth it i f u use at first i ti wil smoke like u bloew a headgastket but
that is just the seafoam

 

Just an option to rule out..... Make sure you didn't put the throttle body in the neck of the carb in backwards. If so it will not allow it to drop and close off. (common mistake)