Acceleration Trouble With Stihl 021

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Good afternoon: Stilhl 021 bogs down on acceleration. It starts OK, 4 or 5 pulls, and runs great at idle. But here's the problem: If the saw has been sitting around, and just idling, it complains and stutters and whines when you pull the trigger up quickly. It will get to full throttle, just takes a few seconds of feathering the trigger gently. OTHER QUESTION: what type of adjusting tool does Stihl use for the high / low speed adjustments? All I can see is a hole, and no idea what goes in it. I use ethanol free fuel with high-quality oil, Power Blend, and have replaced spark plug and air filter. Thank you for your help.