Turns out they aren't the 29 mm carbs...they're 28. Cb750 came stock with 28mm, 500 and 550 had 26 iirc. The mik 28mm will still breathe better because it's a smooth bore. 38mm would be way too big. My bandit 1200 has 36mm carbs. Gsxr1100 had 38. Bigger displacement doesn't always work better with bigger carbs, like any other tune, you have to optimize it for something. For example, a smaller throat carb will deliver better low and midrange power due to higher velocity venturi effect from a smaller throat, but loses flow efficiency at higher rpms. A bigger carb will have less velocity down low but will flow more cfm up top. Cam profile dictates a lot about carb choice. A milder street cam will benefit from a smaller carb for ridability on the street. A high lift, high duration cam will be pretty worthless on the midrange but will benefit from a larger carb that flows efficiently at the rpm that the cam starts to run efficiently. The cam I put in this motor isn't crazy, but is significantly longer and higher than stock and would have really loved the mikuni 29 mm smooth bores...but the 28's will still out-flow the stock keihins. I'd really like to fit a set of keihin CR carbs, or find a rack of 30mm CV carbs that would line up without too much modification. Another option would be to gut my carbs and de-rack them, then chuck them on a lathe and indicate them perfectly on center and bore a mm or two out of the throats. There's enough meat there to do it and the slides are large enough to still function correctly....and I have access to a lathe....it's just a fucking ton of work.