A 12.75x3.75 is not enough prop for the Evolution .61. It’s a lower RPM engine that likes to swing some lumber. Mine turns only 12,000 with at 12 X 6. If you go with the 3.75 pitch, you may want to try a 14" dia. prop, but that may not provide enough forward speed.

Try the Pulse 60 using a 12 X 6 prop first – if it’s too fast then drop down the pitch, but I think it’ll be a good overall flyer with the 12 X 6.

Hogflyer