Chainsaw Repair

The saw has a new carb, fuel line & filter. Vent is clear. One new crank seal.

It runs full speed for 5 minutes or so than starts bogging down. It will die if cutting continues, but speeds up if not. Compression is good. It has never had any electronics replaced

Air leak? Thanks

I had a Poulan 245 doing that while I was trying to tune it up after rebuilding it.  It was flooding the crankcase with fuel until it would splash into the top of the cylinder and drown the spark. i got it under control by leaning out both the L and H needle valves.  I had started with 1 1/2 turns on each as a starting place.  I wound up with L at 1 1/4, and H at 7/8. 

The spark plug was wet right after it would die, that's how I figured it out.   

I had another saw do something like that, in that case the carburetor bowel valve was not closing when the chamber under the diaphragm was full. It was pushing that excess fuel through the jets under pressure.  The little arm which touches the diaphragm was bent, the valve was always held open.

Both saws really used a lot of gas fast.