Hey all,

Just working on a small frame. I have a completed 50 engine that came with the bike (v90) and it was kitted with a Olympia 75 cylinder. I believe that the engine (based on vin) is a 4 speed 50 special ('73-'85).

I have lying around a Dr85 cylinder and piston and wondering if the DR makes a significant difference performance wise vs the Olympia.

According to the SIP website, I would have to change the primaries to a min 3.72 to max 3.0 using a 16mm carb and a banana exhaust to optimize the cylinder. Another option would be to put in a 19mm carb and swap the primaries to 2.86 and a banana exhaust. (for the DR 85)

Now for you gear heads out there, would swapping in the v90 primaries to this 50 engine do the trick? Or would I have to purchase a whole new primary set?

Any other suggestions? Should I just keep the Olympia 75? or go for the dr 85? Could a 90 cylinder and piston fit on a 50 crank?

Goal for the bike would mostly be for putting around---not long haul rides or commuting.

I appreciate your input and suggestions.

Thanks so much.

N