Is this a new engine geo29? This sounds like maybe your too rich on the idle mixture. The idle screw effects the mixture up to about 80% throttle. The manual gives good directions for valve adjustment. The fuel and plug choice sound good. Poor compression shows up at idle first, so that's probably o.k. If it's a used engine, maybe the bearings should be looked at. Run it wide open and lean it for max rpm, then richen it for about a 300 rpm drop. Now adjust the idle for a good transition. If it burbles with lots of smoke, lean it some. If it bogs down or dies with no smoke, richen it some. A 1/8 turn on the idle screw at a time is about right. I use an 11x7 MA on my .52.