Can anybody help me? My sherpa m80 has 520 chain with 11 tooth sprocket on the front, and 40 tooth on the back, but is to fast at low throttle in first gear. Does anyone have any suggestions as to which sizes of sprockets to use. Dont think I can go any smaller on the front so it probably needs larger on the back, but what size?

I think the M80 should run a 52 tooth rear sprocket but with the smaller pitch chain. I have an original 52 tooth sprocket (small pitch) and a 43 tooth for a 520 chain and these are virtually the same diameter. I would suggest a 43 tooth/520 would be about the same gearing as the original 52. However, will this be to your liking? Dave Renham can supply any size 520 sprocket to fit the M80 hub.

Your bike was originally a 13t - 52 t but with 428 chain.

On 520 chain - you need 11t and 46t - if you find this too low - change to a 12 on front.