All the M20 based 720s I've built have run on the standard breather and it seems to cope OK...My B33 at 720cc couldn't cope however, probably down to the higher revs, so I fitted an additional breather valve and that solved the problem...Ian

email (option): ian@wright52.plus.com

Ah, Mr. Wright himself! Thank you for the conformation. I shall proceed on with the stock breather mechanism.

Cheers,

JDE

email (option): teladelujo@msn.com