I ride close to sea level, usually less than 2,000 feet. When I ran the stock Keihin 39mm carb it was set with a 175 to 180 main, needle, if memory serves, 3rd or 4th position. Now I run a 40mm Lectron set by Lectron. I seized pistons under both carbs. The head has been milled and reshaped so I feel relatively confident it's flat but I cannot say definitively that the cylinder has been lapped. I'll be sending it to Millennium for plating so I'll include that too. Good idea!