Have 650 which misses and backfires with no power mostly before it gets completly warmed up. I know someone before wrote about an adjustment screw somewhere.Im not to good with engines but if anyone can help I would sure appreaciate it and tell me just where that screw is. The temp was 14 degrees and the machine started just fine without using the throttle,but when I rev up the engine or go to move it starts backfiring and missing. Plugs have been replaced as wellas the choke cables.

 

If it stop's doing it after it warms up I wouldn't mess with it,That's why you don't need to take off until it warm's up, mine cough's and spit's until it warms up also, after a few minute's it takes gas fine, you can richen the air screw adjustment but it may idle to rich when the weather warm's up.

 

Based on what you said you should probably back out (turn left) the two pilot screws on the carb 1/4 turn each. They are on the right side if you are sitting on the machine. This should take care of it.