I found that I had to switch to a hotter A3 plug, mine just wouldn't tune with the cylinder horizontal. You couldn't get past half throttle, and it would load up and die. I ended up pulling the motor and putting it in a different plane, mounted vertically, and readjusted the needles, and it ran fine. It took about 3 - 5 min. to get it tuned. Once put back in the Rocket, it would start, and run up to about half throttle, and die. Once I switched to the A3 plug, it runs fine.