mnrcaerobat ,
The smith mini is my favorite "quick run to the field and fly" airplane.
I can fit it in the back seat of my 4 door sedan without any disassembly and nobody ever recognizes it as the smith mini.
Don't see many of the mini's around anymore. It's and older kit.
Yes, It definatley gains altitude during full throttle.
Can't do anything but trim it down.

I run the new Saito 56 in it and flies perfectly, but is not over powered.
I think the old OS fs 61 (4 strk) would be ideal.
A 72 4 stroke would be over kill.

Nothing like a serious flying plane.....no set up time, assembly or losing wing bolts.
Just take it out, fuel it up and flyit!

Jeff