I have an ata125d atv. It was bogging down when trying to accelerate and on the stock carburetor they made it to where you can't take apart the bowl to clean it. Ordered a new carb and put it on, and now it seems as if I can't get enough fuel. I have the mixture screw richened all the way, and the idle almost to where it moves itself in drive. If I lean it out even a quarter turn it dies and after revving the engine up or putting a load on, it idles too low and stalls. Any ideas? Seems to run pretty good otherwise. Just need to idle it up more?

 

I have a Coolster 3125R and I had the same problem and it was sucking air through the intake manifold mating surfaces - both between the carb and the manifold, and between the manifold and the engine block. You could try tightening the bolts or remove the carb and manifold and seal with gasket sealer. If tightening, be careful not the strip the threads in the block where the two bolts clamp the manifold down. You can get the little motor to idle pretty smoothly once you take care of the air leaks.

 

Also found it idles and runs much smoother by replacing the stock air filter with a Uni dual stage filter and running 91 octane ethanol free gas.