First starts - clipped combat prop 4.5x2.75 - too much shaft load I think, can't get it past overrich low speed or starving for fuel.
Just returned from the basement - now it's 3.8x2.75 (and carefully balanced).
I am not really sure how to mentally equate 1 blade to 2 blade shaft loads. These would normally run a SB 2.875 x 4.0-4.5 or so, that means it scribes a 5.25 diameter circle.
MJD..I've lost track of what you're doing. Are you running it with a pipe..?
I found that a 4.2 x 4 was marginally too much for a piped .061. It was better for the engine with the airfoils thinned out. If you take 4.2 x 4.2 x 4 =70.56...that gives you a load factor that I'd say is too much for a new engine that you are playing with. Consider the 4.2 x 4 "swinging for the fence".
I could have been using too much compression and nitro...I don't remember those details. I wasn't using any more than 10 or 15% nitro, but I wasn't being very careful about my approach.