Stihl 020 AVP problems......runs at 1/2 speed

[DarylJ]

My Stihl 020 AVP runs perfect until it gets warmed up. Then, it will suddenly run at only 1/2 speed, no matter how much the trigger is pulled. Just one speed. Kind of like it is firing every other revolution. Just as suddenly, it will instantly be fine again. Then, after a few seconds, back to the 1/2 speed thing again. Could this be a coil issue? If not, what might be causing this behavior? I have had it to a repair shop. They didn't run it long enough to observe a problem. I also had the carburetor completely disassembled myself, and cleaned it thoroughly. It starts easier than before, but still has the same old 1/2 throttle issue. Any ideas on what is causing this are sure appreciated!!