Originally Posted by B-Rod
An FCR on a 640 would be fun fun fun. Maybe fire off a message or call Motolab. He might have some jetting suggestions, or even JDjetting. To me a 162 main at sea level sounds lean for the air a 625cc pumps through
162 is the closest of the 2 jets I have on hand, remember the SXC with a 41 FCR only runs a 165 in stock form... My airbox has been left stock so the current jetting shouldn't be too far off...