my attitude to the vm18 is its pointless unless theres work done on the ports. the standard intake is approx 14mm ID. ideally, you would use a 14mm carb, there being no mikuni in such a size, one must get a dremel! using a carby larger than necessary causes low speed bogging, especially with sudden throttle openings.
then again, if the ports have been opened up to allow an 18 carb, the mikuni is so easy to tune in and use, that its worth the effort.
you need to remove a LOT of material!
then, going to a 22, 24 or anything else is simply ludicrous...
vm16 or 18. best buy.
the ones that are sold for under $100 are invariably chinese copies, they are not genuine mikunis... do the same job, but arent genuine, despite the stampings.