RE: TT GP 42 Engine Leaking and compression decline
We also used these engines on our club planes. They do not like to run hot, they lose compression very fast. Do the crock pot (anti-freeze) cleaning method to get rid of any gunk that has baked on. After that, do not spend alot of time leaning it out on the ground, it will get hot fast again. If it is still fresh, it may take some time to break-in properly before it will handle max rpm. With a 10x6 MA prop, most get around 13,000 on the ground some up around 13,300 (stock muffler) If you use a 9" prop, you might get more. But this is a sport set up, and won't do big numbers. OS 8 plug works good too, 10-15% nitro max.