Originally Posted by Lenz1
Mr Le Feesh
Odd that you suggest "exhaust valves sucking oil" - why is that exactly
Changing valve sizes is a world of pain that only leads to a series of on-going engine spec changes.
Easy performance gains are available with a little careful porting and a slight rise in compression.
If 500cc power is what you're after then the cost and time effective solution is to buy a 500cc bike at the outset.
Going down long grades it will start smoking, it is sucking oil past the exhaust valve seals. Then after leveling off it will continue to smoke until it burns out then is good.