Hi there hope anyone can help

I am having a lot of trouble with my OS Max 40 engine that I have installed in a SPAD plane. The engine has the following problems as I can see them;
1. The engine doesn't like throttle transition, andis 'jerky' and takes on final approach
2. After much less than half a tank, the engine starts to quit.

Any ideas about these symptoms? Any help much appreciated!
Regards
Gareth