RE: rich or lean gas?
The 2.4 on the 300 was a simple problem. Too small an engine on too heavy a plane. The wing area on the Midwest was a little on the short side, too.
That brings up another subject that's so often overlooked. Wing areas. A lot of people see a new plane hit the market and the go "OOh, a new Extra, Yak, or Edge. That should fly great." But they often fail to take the wing area for the suggested plane weight into consideration. A heavy plane with too little area will fly like a powered brick, even worse with a larger engine. A heavy plane with a plentiful wing area can fly very well with a smaller engine than the plane with less area. That's why so many heavy robotic aircraft fly so well and so long with relatively tiny engines. Combine weight with large wing area along with clean airframes and smaller engines can be used.