Jeez, I never looked that closely at those engines before. That's a hoot. Maybe they were trying to do 14 pushrod tubes and got confused about what they should look like.

The air flowing past the cylinder head hole in the cowl should create a low pressure area, but your theory could also be correct, due to the angle on the cowl at that point. If so, they'll run hotter than before, no question, now that I've close off half of the flaps. If that happens, I think I'll put a reverse scoop over the hole, with just a small hole in the center for the glow driver.

Four strokes seem to have completely different cooling needs. The muffler gets hotter than anything else on them, just the opposite of 2 strokes. I have a friend with an SE-5 that has an OS 91FS, and he has it completely boxed in with NO cooling air, just the muffler hanging out the bottom, if I remember right, and it does just fine. Backfires every now and then, but he likes that. Go figure.

I'll run her up as soon as I get my therm, and post the results.