Hi Bill, I have an ST34 heli engine that was bought 10 years ago in a Shuttle ZX package. I'm not sure if its a 34G like the current one, as I have lost all the manuals that came with it. I had an OS no 8 plug in it at that time and couldn't get it to run without the engine cutting out just before lift off, so I gave up learning to fly then. After 10 years of having the model as a display piece, I've decided to give myself a second shot at helis so I'm wondering whether I had made the wrong choice of having a no8 plug in there. Should I try something else?

With a 10%-15% nitro fuel, and O.S. Max #8 plug should be fine. Most likely, the engine was never broken-in properly. It would be best to mount it on a stand with a prop and spend the time to get it well broken in. Unless you can fly a heli at full throttle and anticipate autorotation, it's not easy to get a good breakin when the engine's mounted in the heli. A lot of good engines have been ruined by attempting to break in an engine while it's mounted in the heli.