It sounds like it is loading up with fuel in the crankcase. Leaning the low end would help. My goal is always use the 25 second period of idle before giving it throttle to check acceleration. I don't do pinch tests. If you can get it to idle 25-30 seconds and transition to full throttle you should be good to go. This takes fiddling with the low speed needle settings until you get it right where it should be. Some people are happy with just getting in the ball park.

I'm not that familiar with this engine, but tuning it the best you can and trying out an A3 plug wouldn't hurt. I don't know if it is too hot for that engine.