[zingshoen]

Originally Posted by Ariel Red Hunter

I guess there is some confusion on Mikuni Carburetor sizes. The model number, like VM 26 refers to the diameter of the venturi. The VM 26 is also called a 30mm carburetor. That is because it measures 30 mm at where it bolts on to the engine. Carburetors have always been measured by the venturi size. All of these carbs are descended, in design, from the English Amal. It is easy to over carburate an engine. A 26 mm carb is close to a 1 1/16th inch Amal. Really fast 250's had 1 1/8th Amals, or about 27 mm venturi. So a 26 mm has proven very good on 229 cc singles. Unfortunatly, Mikuni does not offer a VM 27. I suspect that a VM 28 is just too big without extensive engine tuning, or hopping up. You will also loose low range sharpness by going to a VM 28, or, in other words, flexibility.

the guy at topham carbies gave me the specs for the VM28 which work on 180cc racing engines, so rather than engine tuning, one could try fine tuning the carbie - i think it works, but not everyone has been successful; using the VM26 should also work. a flat slide is where the difference kicks in.