Is this a 250 or 500? If it's a 250 the stock mikuni tm34 bored out works good or a stock tm38 from a zilla. If it's a zilla get a Stock tm38 and send it to Jerry Hall to be bored out to 41.5. Keihin and lectrons are notoriously hard to tune. I run Mikuni's on everything but my, 87 250x.