Scooterotica

I`ve used the same 62%+72% for engines from 50cc vespas to suzuki gt750 tripples.

these are about the maximum you can use with good port shaping, ie fairly oval sides to the ports.

no doubt somone who knows more about lambrettas than I do will have other advise

i think the formula is the same no matter what size bore, its all about the ringpieces, you might get away with it if you use a decent piston and thin wire ring/rings but on a standard piston and rings at 72% it will probably s**t itself, ive never gone 72% myself but no doubt some on here have exceded it, even 70% will give you more ring wear.

I take it you are all talking chord length here and not around the bore ?

I am