Did you replace the flywheel? IF so, did you torque the flywheel to 150 ft. lbs with a torque wrench? IF not, could be flywheel key. Sounds to me like you are not getting fuel before. I would remove the carb solenoid, depress the plunger, wedge a tooth pick beside it, break the tooth pick off holding the plunger depressed and see if engine runs OK after you get the starting problem solved.
