My MVVS 40 also required a longer break in period than I was used to (hey most of my engines are TTs and OSs). It took nearly a quart of FAI before I was comfortable in the air with it. Probably another half gallon before it started to transition well. But now with over 1/2 gallon of FAI, 1/4 gallon of 5%, and 1/4 gallon of 15% run through it, it's become a wildly fun engine to run, especially with the growl of the tuned pipe!

BTW, I took out the plug that came with the engine shortly after receiving it because it wouldn't idle worth a damn with it and put on an OS #8. I recent put the Rossi R5 back on the engine and started using 15% nitro without issue (and now it idles fine with this plug also). From what I understand, I have a newer 40 (bought it in October from Morris) which may be more tolerant to nitro than older models.