Shouldn't need to be at full throttle to start it. Matter of fact, that's rather dangerous.

Do you have the instructions? If not get them from OS's website. If this is a new engine, follow the directions exactally, break the engine in IAW the manual. Sounds like you have an air leak somewhere, should shut down immedieatly with throttle barrel closed, or is it not closing all the way?

In any case, I hate to sound insulting, but get and read instructions..... and post more info (how long has engine run, needle settings, etc etc, what's it on, as much as you can think of)

Andy