WeedWacker Friction drive help?

We ran the R/C conversions with turned down flywheels with free air cooling. There was a big fan up front of course. They did pick up a small amount of power not turning the cooling blades. In fact Rotax listed the free air cooled versions of their ultralight engines 2hp higher. Most fan cooled engines have the fins on the head aligned for the forced cooling air, and are not aligned for free air flow. Also the ignition module is cooled by the forced air. It becomes a wonderful heat sink if the engines temps get excessive while stopped. I agree that in the real world the little engines survive in free air, but personally I would run the shroud to give the little fella all the help I could. The air forced by the cooling system is far greater than the 20mph aerodynamically dirty breeze easing down the road.

The air forced by the cooling system is far greater than the 20mph aerodynamically dirty breeze easing down the road.

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That may very well be right, CB.
I'd like to see that tested scientifically, just for curiosity. I mean, which is cooled better, a bare or shrouded motor on a bike? I've never noticed any big flow of air blowing out of a weed trimmer's flywheel/cooling system while trimming.
For sure, in normal weed trimming use they are basically stationary so you need the fin/shroud system. Many other 2-stroke air-cooled, mobile (bike) motors don't have fans or shrouds.

I'm not at all trying to argue with you, Cannonball. I would bet you know more about motors and MBs than me! The OP said it was running hot. No telling what he did or meant. These things are so hard to try to diagnose with little info. Your mention of a possibly overheated ignition module was good.

Just wanted to say that the lack of a shroud is probably not going to cause a well-adjusted 2-stroke motor any problems on a bike. China Girls ain't gonna look so cool all covered up!

No I agree that practically free air works, but with the forced air cooling there is no doubt.

A dam, just had to point out the irony of the above statement as I sawed the fan blades off my Maytag for my latest build. Have to keep her moving!