OK this might not be a tuning issue.

When you replaced the clutch bits, you had to take the engine out right?

On this point when you refitted the engine did you set the tooth mesh correctly?

A way of checking is to put the buggy on the floor, release the brakes and try to push the buggy, if its too tight then you'll find you struggle to move it. This friction is what is stoping the engine from starting.