[gnr racer]

I have a Novarossi +4 myself,just about to go on to its 4th gallon, best engine i have owned absolutely faultless.
If you are looking to get another engine, the Alpha .21 range seem to be v.good (I've just bought a 2nd hand 850f) stripped it down & it looks to be v.good quality for the money & spares are cheap...conrod £15, but a very tight engine to break in aparantly.
I had a go gxr but didnt get on with it at all, I would say try an Alpha