Now fine tune the main jet with plug checks. Plug checks are the key to fine tuning the main jet once the other circuits are set. Rich Look for symmetrical burn patterns, smell for odors like burnt plastic, which is actually tranny fluid and would be indicative of a blown seal. This is a lean symptom and often occurs when a motor is cold. Try turning the air-fuel screw clockwise a quarter turn richer and check throttle response again until motor revs without hesitation.
Motor knock knock knocks at idle when hot.
Motor revs clean and crisp but runs really hot and lacks power. If you are on the trail and don't have the right main jet, try raising the needle by lowering the clip. It won't be exact but at least you won't seize. If better, your problem is a lean condition. These jetting tips are provided courtesty of Alex Dicharry from DNA Racing.