Hi!
Being into pylonracing for many years I can give you some advise.
If an engine doesn't put out as much power as expected you have to take the engine apart and check for a worn piston to cylinder fit. The piston to cylinder fit is very important.
If the piston is so worn it can be pushed out trough the top of the cylinder liner it is totally worn out and has to be discarded.
Second... for best performance in every airplane it is vital that you use the best tank available and that is to use the Tettra line of Bubbleless fueltanks. 85cc (3 1/2 oz) and up is available.
These tanks are used by pylonracers world wide for their reliability.

Regards!
Jan K
Sweden