Hi all

I have an old Thunder Tiger 91 Four Stroke that a friend gave me. It's seems to be be quite old as it has one of those sliding choke levers and just looks old. The engine is inverted in a Hangar-9 Spitfire.

For quite some time I really battled to get a consistent idle from the engine. From fiddling with the low end to checking the valve gap, cleaning it inside out. I have tried it all. Eventually I managed to get it to idle slow enough that my plane does not creep forward when it's on the runway ready to take off. But still not as good of an idle as I get on my other four bangers.

I noticed that once I have had a flight and have come in to land that I can trim the idle down by about 10 clicks and then she idles fairly well. When it's cold I realy have to crank up the throttle trim again. The engine also turns over relatively easy with seemingly less compression than my other four strokes. And quite oddly is much easier to start when warm that when cold. A friend of mine has a Hangr-9 Miss America with an OS91FS and he just seems to get oodles more power out of that engine (No no no, lets not start a OS vs TT debate here)

Is it possible that the engine needs a new piston ring?

Marcel