Decent compression tester at a auto store is around $25, and if the cylinders can hold above 110 PSI, should be ok. You can look at the skirts from the exhaust and carb side for any piston wear.
If it were me, I still would pull the cylinders, "AFTER" going through the carbs again. BC Dan has a good theory going about the main jet, tuff to go through 10 gallons of Gas in 40 miles. Stock jetting?
Clutching will also pull down the RPM's, bad spring in the secondary, pulling belt down prematurely. If you lift the back end up, can the motor pull 8K without weight on the sled?