My CRRCPRO GF50I motor seems to work for the first 5-10 minutes of flight and then suddenly slows to idle, After a minute or so the speed picks up again. All the other control surfaces carry on working normally. Ground testing has not solved the problem. I have also checked the fuel filters but no problem there either
Any ideas

This should be in the Gas engine section.You'll find more answers there.
maybe you have a pump diaghram issue

I see you already posted there,never mind

My first thought is it is lean and getting hot that is why it slows down.

Larry S