I broke in this engine a week ago. It's had about 3/4 of a gallon through it. I love the top end power. I had some problems tuning it. Finally, I changed the plug from a #6 (which it came with) to a #5 and it's been behaving alot better.

I have been using the 7.0 venturi from my MR21 b01a instead of the 8.0 that it came with. Were some of my problems due to changing the venturi? Which venturi did yours come with?