Hi Did I read your post correct and your running a 40-1 mix. If so change that pronto to 20-1 there are no needle bearings in the rod on that engine and it will self destruct due to poor lubrication. Which also could be causeing a lower RPM.
Now as far as your cam timing you will need to pull the cam cover and the outside lifter to see the cam dot as Jim said if it is correct reassemble recheck the valve clearance and look elsewhere. As a rule you can retard the timing a little to gain more power to swing more prop but run lesser RPM's. Myself I set everything at 28 and forget it.