sync the carbs .......................... how when you have this situation?

arent those vents?

The exploded views shown in these links aren't really clear or detailed enough for definite answer (same image is shown in the Sudco Mikuni catalog 4th edition); however, fwiw, the parts listing do include #22 "air vent hose" and #63 "vacuum cap."


Exploded view


Another exploded view


Would presume there to be at least one air vent (perhaps two air vents) serving the four float bowls. And guessing maybe one vacuum nipple fitting (as pictured?)
for a vacuum petcock if so fitted.

With engine running, should easily determine if there's vacuum at the pictured fitting. If not used for a vacuum petcock, should probably be capped so as not to constitute an intake air leak.

Admittedly just guessing.

Regarding synchronizing Mikuni carbs, the Sudo manual recommends that all smoothbore type carbs be synchcronized mechanically rather than with vacuum gauges or mercury manometer, and specifies several reasons why vacuum synchronization is not recommended. I don't understand this because the reasons given would seem applicable to any carb where the tops are removed to access the adjusting mechanism.

Regarding 29 smoothbores, I rely on wiredgeorge's experience and advice (from earlier threads) and perform both mechanical synch follwed by vacuum synch (as described in the FSM for oem Mikuni manual slide carbs, using the oem carb holder nipples).

Good Luck!

You are right, there is one a vacuum fitting on the #3 carburetor. There are two vents positioned between 1 &2 and 3&4 plus two fuel inlets. The inlets join to a single pipe system so you really only need to feed in gas through one of them and cap the other. I would guess the twin inlets are for REAL high performance bikes that would use a bunch more gas than my test bikes. The vacuum fitting is capped in this pic on the #3 carb. As far as just mechanical sync of VM29s, I take that as seriously as I do their jetting recommendations. Neither makes a lot of sense in the real world.

Im not 100% sure but I think if you get factory 34mm CV carb boots they have the fittings where as the aftermarket ones dont. Its been 15 years since I had the 33s but thats what I recall. I traded then for 29s

None of the constant velocity carb holders have vacuum fittings now or in the past for Mik/Kaw applications.

Well, I guess I was wrong, 15 years is a long time for a 64 1/2 that doesnt remember what he did 10 minutes ago

I think an easy solution would be to take your carbs off and plug the intakes with a wet rag then drill and tap the intake and install small barbed fittings or nitrous fittings,think it could work, thats my (2) cents.

i bought my uni-sync tool from a performance auto parts place it was made by edelbrock i've used it on my lectrons my 37.5 round slide mikunis and lot's of snowmobile two stroke set-ups that don't have a vacuam port for obvious reasons it works fine. the trick is to bench sync them as close as you can and do it quickly if get a lot of heat in the motor shut it down cool it off try again. the trick is to not let a lot of heat build up.

i gapped out for a few minites i the carbs share a linkage you can't use the uni-sync tool in order to use it you have to have individual carbs sorry i did't mean to add to the confusion.

School Teacher - any luck on getting those 33's synched?? I need to synchronize a set myself and I'm not sure how to do it.

I hate threads with no ending! :laugh:

Would adding a set of NOS manifolds affect how the carbs run? Seems like it would be easy to add a vacuum port where the nozzles would normally go. A set of APE manifolds are show below for reference: