1. Bike runs rich and has a backfire problem... Is there an easy soution to this problem?
2. There is a crack in the Crankcase that has been fixed for the short term with a bit of Liquid Metal... good stuff.. However I would love to get my hands on a second hand crankcase .. or maybe even a new engine .. I don't know how long the crack has been there and if it has caused more damage inside the engine... Any suggestions.

3. I are the engines for the D1 and C models the same? Can I swap and change parts?

... Taking it in to the bike shop in 2 days to see what they say....