RE: Super Tiger 40 problem
What size prop are you using? I'd use a 10x6 for break-in as this puts a good, safe load on a forty. Also, make sure the engine is tightly secured in the test stand. Once I had a new engine that was loose in the stand and this caused the throttle arm to constantly move while the push rod stayed still. At first I thought the prop was slipping and causing the rpms to surge. So, also make sure the prop nut is tight.
David