Engine Trouble keeping speed problem

Alright so let me start off by saying its a 66cc FM80 on arm have a stock nt crab jet pin is set in the middle. Having a problem. It idles fine when sitting. It accelerates and slows down fine but keeping at a speed above 20 its sounds like its 4 stroking and feels like its going in and out of power. No idea what is going on. I am running 74:1 using 1 packet of Opti-2. New sparkplug set at .022. Any suggestion(s) would be super helpful.

try lowering your needle a notch before doing any jet work - if it runs better, then either try one more notch or get about a half notch by lowering float level