wjcalhoun

Gentlemen:

I appreciate very much your outstanding and very helpful suggestions. RCPilot - I like the air dam idea, and will incorporate that also. Looks like a small lip - perhaps 1/4 - 3/8 might be enough to increase outflow draft.

I am thoroughly embarrassed to say that I identified and corrected the problem today. Those of you who said my mixture was too lean were right on the money (in my specific case - the general suggestions are most helpful in a more general sense, and will inform how I build and configure planes in the future).

I found a tiny split in my pressure line between the muffler nipple and the tank; it was small, but clearly enough to release muffler pressure. Hence, the tank was not pressurized, and my engine had to pull fuel, and therefore experienced very lean conditions in flight. I found the split today at the field, replaced that small segment of line (between the muffler and my pressure line fuel filter), and immediately had to lean my mixture screw by 1 full turn! Obviously tank pressure enhances fuel flow, and lack thereof starves the engine.

With that sole change, the problem went away. I did fly the plane first without cowl, and engine temps seemed normal [spit test evaporated, but did not sizzle :-) ]. I replaced the cowl, and flew again, once again without any hint of overheating.

I will still install the air dam to enhance outflow, and will still block my port side air intake to encourage airflow over the cylinder fins. Just make sense to me to protect my investment in my engine. It does remind me of the basics - a hot engine is either lean or starved of cooling air (or maybe has a bad bearing).

Thanks to all for your very helpful suggestions! This is a great hobby.

Bill