I dropped the bottom cylinder (not firing) after 10 to 15 minutes of operation---compression is good---carb clean --no water in fuel--replaced coil, ECM, stator and trigger and still the problem persists---talked to my shop and they think it might be the crank seal. after it has sat for some time it will fire on 3 cylinders for 10 or 15 minutes again. I NEED HELP QUICK