Zenoah and Fuji are both outstanding. Desert Aircraft is another good one. Iam really impressed with the DLE's too and plan on using one on a current project. Even some of the "no-name", low cost Chinese engines run very well for the money.

Iwould not be concerned about fighting to make a gas engine run. If somebody was struggling that bad with one then there was either something wrong with it, it was set up improperly or he did not know what he was doing. Gas engines are almost always easy to start, run great and don't require a lot of fiddling once the carb is adjusted.

For that 3D plane, take alook at the DLE-30. If you want something larger, there are plenty of 40-43cc engines out there. That Fuji-43EI is a little pricey but it is one of the most reliable, best running gas engines I have seen.