Just yesterday I helped a new guy in the club... He has an Evolution engine in his H-9/P-51 Mustang.

My experience with that is exactly the same as you just described. I spent nearly 2 hours with this engine at the field, I finally decided to take it home with me to do some research and fix the 'Idiot Proof" engine as this was the FIRST engine I was unable to properly tune [:@]. Do a search on here for the engine tuning fix.

Hint: You'll need to remove the pins that limit the low speed and the high speed needles, that is step one.

With the limiters in place, you'll NEVER be able to properly tune the engine for reliability.

EDIT: This engine now runs like a champ... no dead-stick landings, sputtering, die from advancing throttle movement and un-even transitioning of throttle changes. It runs about as well as an O.S. engine now.