How tight are your loops, and how long can you fly inverted? Here is a list of causes:

Your tank may be too far back, down, or up. If it is too far up your engine could be flooding, and if it is too far back or down then it is leaning out and quitting.

If it is quitting on the downside of the loop, its running too rich. If it is quitting on the upside of the loop, it is running to lean.



Give me more specificis on where in the loop it is quitting, what other aerobatics you can preform without it quitting, and how long you can fly inverted. It's s simple problem, I just need more info.