Could be maybe you've cut out too much on the front when you should have cut out more on the bottom rear of the cowl as that is where the cooling air has to exit. I have a Pitts with a Fuji 50 and have ran it about one and a half hours with no problem. This was just break-in runs in the garage however, as mine has not flown. I don't know this for a fact, but it seems to me I read something to this effect in a post on the old rcairport site. Anybody else have any thoughts?
CL