RE: Cox .074
I still have a couple three of the .074 Queen Bee engines and the ones I ran all worked OK. They aren't super power engines like some guys were hoping for but they work OK. I think some people expected more from the engines but at the time that was not what Cox was marketing or making the engines for. They are a decent good sport engine in the .074 engine displacement range.
The muffler does restrict the engine a lot, but nowadays we have to use them, so one just gets used to it and the less power you have accordingly.
At the time that 1/2a engines were really popular. The .09 and .10 engines were all denegrated and looked down upon as being under powered and too heavy. I remember guys bad mouthing the .10 engines all the time stating a good .049 engine weighed less and had more power than the .09's or .10 engines had.
The trick is to choose a airplane to better match the engine's power potential for the best flights.