Hello,
I have a Avistar trainer with thunder tiger 42 engine with a 10/6 prob.
I'm facing a problem that my engine during flight( not on ground)
stack on a low rpm and doesn't respond to turtle changes.
what i did is:

1) checked the fuel tank for sealing and it OK
2) i install a new glow plug
3) i cleaned the fuel valve
4) i cleaned the head head of the engine
5) on the ground when i'm moving from idle to full theengine respond well

the problem is still there.
i have two more assumption , one is that the fuel tank is not located at the right position, the second is that the prob is to big.
i will be happy to hear more idea and details of the location of the fuel tank related to the engine.