i thought when an engine has extremely low compression when warm/hot and its difficult to start, the engine was shot, i know in my cars, when they are difficult to start when hot and little compression, its time to change the piston and sleeve. i just see in the heading of the thread it says low compression when hot. An abc engine should loose some compression when hot but be able to start still, without an electric starter. i never noticed a compression drop in a plane, i usually run os engines and they run excellent and usually dont need to be restarted. I do have an mds that i still cant seem to get running, its brand new but has the black head, i think its a .46. very hard to make idle and even harder to keep running, i think i am using too high of a nitro content.