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hi guys . this seem to be the place for good info so hope you can help . have a z1 with 1075 big bore . in process of rebuilding whole bike . had a succession of standard carbs but am wondering if am not getting best . could someone explain the differance between the mikuni range that could be used on this bike . ie vm29 smoothbore . have seen adverts for 33mm smoothbore that state for z1 ???? are the outside diameters of the inlets the same or would head work need doing . what options do i have lads . sorry to be a novice . will post picturre when bike is finished early summer .

The OEM VM28SC is adequate for flowing gas for a stock Z1B but once you have added displacement, bumped compression and added aftermarket cam shafts, the need for MORE air/fuel to achieve optimum performance becomes necessary as you may have discovered. The EARLY Z1/Z1A carbs flow THE MOST air/fuel of any of the OEM Mikuni carbs that will fit your bike. Quite a bit more air/fuel than the Z1B carb which was tamed down a bit from the 73/74 models. The problem is, that the Z1/Z1A versions of the VM28SC are limited by the size of the fuel pipes that carry fuel internally. They are relatively small. The VM29 smoothbore presents a pretty good performance enhancement as its fuel pipes and method of atomizing fuel are a bit better than the early Z1/Z1A carbs and its synchronization method is a LOT better. The early carbs were a tad hard to tune. The downside of the VM29 smoothbore is the idle circuit which is a tad on the fussy side. I have never figured out why they made the idle circuit so darn tunable since races are not won running on a pilot jet or at idle. In any case, there ARE ways to make the VM29 more easily tuned and these modifications are known to folks who have worked on a number of sets. The VM33 obviously has a much larger venturi and is capable of moving more gas/air but moves the horsepower upwards in the RPM range. It is also somewhat even more difficult to tune at idle and at mid-range. This is why the VM29 commands far higher prices than does the VM33 which would be more appropriate for racing than the street in many applications. Another dandy alternative to the round slide (VM series) carburetor is the constant velocity carburetor (Mikuni BS34). These carburetors have a larger venturis and can move sufficient gas for any moderately punched out bike with performance mods; like your own will be. The BS34 requires the use of larger intake manifolds than does the VM29 and you will probably want to use pod air filters. It also uses a single and different style throttle cable. The advantage of the BS34 is that it is SMOOTH through the entire range of operation and easy to tune and parts are readily available. The smoothbore carbs have not been available for sometime and some parts are hard to find, if broken. Check the Sudco web site to see what parts and what prices the smoothbore parts are today. I have tested quite a few sets of carburetors over the past couple years in my business and the BS34s would be my personal choice. They are what I am going to install on my KZ1000E1 project bike. I have more information on carburetors in the link on my signature.

you are the dogs bollox george . its so nice to get clear concise info . have taken it on board and will look out for some 34s . engine is standard apart from the bore which was a necessity . would it be worth a change in camms as the stocks are in good cond but i am open to advice and any advice on donner manifold rubbers would be greatly recievd . as i say bike is being rebuilt . frame modified with gsxr front and back end so dont have to right letter to brakes when junctions sneek up on me . must go the wife wants engine covers out of dishwasher lol

can some one post a pic of the bs34 carbs please. need to see them!!!note really sure what they look like.


i thin i just bought these carbs.