Whatever Racecity has already said- Ditto. I have a .61 and a .77 and both are absolute powerhouses especially the .77 . Mine run great on FAI fuel but I seem to get a little better idle with 5%. MVVS makes a variety of mufflers and pipes (both tuned and muffled) to fit your application. The earlier .77's had a needle valve that was a little tricky to get set right, but the new ones have a different tapered needle that is not so sensitive. I have nothing but good things to say about my MVVS's.