That is for only the a/f adjuster knob not the carb
I put a 25mm from an ATC185 on my x15..although there were clearance issues there was also a way to solve it.............As one of the other forum users recently found out, the carbs with that type of float bowl will have clearance issues with the head. The one i posted above is a direct bolt in replacement and will fit perfectly. And it is a few bucks cheaper.
Well then forget my responses. You are probably going to have to do some trial-error and maybe make a custom manifold to get a carb to fit. But still, a carb with a smaller bowl will most likely be easier to fit...so said i was running a x18 engine.....im using a 3 valve SDG with 5 disc clutch...