OS-140 Idle problem
 

I have an OS-140.
It used to run OK. Now I can't get the idle less than 2,500-2,600 RPM.


It has 190 flights. I use 15% nitro, 15.5*12 4 blade prop, OS tuned pipe.
The bearings anged were changed befor 90 flights.
I could not detect any bubbles in the fuel lines.
The max RPM is about 7,800 (as before).

What could be the problem?
Thanks
Eli