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I'm working on a ht101 sthil 4mix pole saw it want RPM up when you pull trigger it cranks and idles but that all but after it runs about minute it will start to rpm up some if you hold trigger wide open, I have change plug adjusted valves clean carb and than tried new carb try it with muffler off fuel fliter is clean,got and ideas?

To me, It sounds like the mixture is off. You do have to keep in mind they need to be tuned like a 4 stroke. I haven't messed around with the 4 mixes, they came out just after I got out of that game

May want to check the exhaust for partial plugging. Around here there is a small bee that likes to plug exhaust pipes. Effects 2 stroke more than 4 but worth checking.

Have you checked the throttle cable for freedom of movement ..??

thanks for the replays, yes the throttle cable is moveing carb flap wide open just want RPM up, and same mix runs 4mix weedeater fine, i'm thinking its coil?

Is the butterfly valve in the carburetor smoothly opening if you slowly pull throttle, or does it catch and "snap" wide open with only a little throttle.

I'd check your high mixture before going to the coil, that sounds like the issue to me. Do you have three adjustment screws or only one? When coils go bad it's usually a work/not working random issue or they will only work hot, etc.

the butterfly works fine, and I tried new carb and still same thing.

I second "checking for plugged exhaust". I have a 2-stroke Stihl (FP 45?) string trimmer that started dogging down and would not achieve high RPM. It would start and idle fine, but when you started opening the throttle it would dog down and act like it was bad fuel, a plugged air cleaner, or lacking in fuel delivery.

I disassembled the muffler and discovered (what I assume is..) the spark arrestor was plugged with oily residue. I took the screen and heated it red-hot with a propane torch long enough for the residue to turn to ash. I then cleaned it up with a wire brush and some carb cleaner and several years later it still runs like a top!

I don't think the muffler is the problem, the op has run the machine without the muffler on.

This really does sound like a mixture issue. Does your carb have only one adjustment screw?2?3?