Mine had a siphoning problem. Fixed that and have nothing but "praise" for this engine. It seems that it needs a little tuning to get it right. Mine was WAY too rich when I got it. After setting the needles, it runs great. Idles low and steady, transitions nicely, and has gobs of power.

Try the pinch test to check your settings. I would bet you are still a little rich on the low speed setting.