Hobbs:

If the valves are tight it will be hard to start and run roughly at low rpm, but the high end should be strong. If the valves are too tight it wont have much compression, still be hard to start, and not much power at the top end. What little top end it has.

If the compression feels good your problem is most likely not valve clearance. It is a good thing to check it anyway, even if you know the service history of the engine.

Enya four strokes are the "Odd ducks" of model engines, instead of having a single cam shaft they have two side by side in the rear case. If some one has had the cover off either or both cams could be out of time. My "Saito trick" for checking valve timing will not work on the twin cam engines, you have to pull the cover and check the marks.

It's also possible the ring is just worn out.

Pull the rocker cover and turn the crank to get the piston to the top of its stroke, if you see the rockers moving as you pass TDC turn the crank another full turn, get the piston between the compression abd power strokes at TDC. Adjust both between 0.0015" and 0.002" clearance. Nominal clearance is OK up to 0.004" but better power comes with the lowered clearance, and the valve gear has an easier time of it too.

Bill.