I want to change my m20 to an m21. I know I need an m21 crank and piston. A friend told me I will need to change the carby as well. What size carby? And is there anything else I need to do for the conversion?

The inlet port and carb are 1 1/16" for the M21 as opposed to 1" for the M20 and the main jet is a different size also...(160 M21, 170 M20)...Apart from this, and the flywheels and pistons, the engines are identical.
Check out the sprocket sizes as well...The M21 pulls taller gearing as standard...Ian

When I upgraded my M20 to M21 spec I found that the few barrels that I checked, including my own , already had a 1 1/16" inlet port. Ron

email (option): ronpier@talk21.com