Topic: 29mm smoothbore mikuni off a KZ650

[garretcb750]

I was given 2 parts bikes (77/78 KZ650) i read on here that the 29mm smoothbores are a nice carb. I also found the adapters from Cycle X and Dyno man. I know these carbs were used on many different Kawi's and Suzuki's with different racks and carb spaceing. what rack from what year bike/model will i need to make work with my 75' CB750F with the adapters.

[garretcb750]

Anyone? know what model year the smoothbores can come of a bike and fit the sohc pre 75?

[Soos]

Dunno... but if you send them to me with re-build kits, i'd gladly try them out for ya!!

 

l8r

[garretcb750]

HA..well I do have 2 sets and both seem in good shape. I might sell them for a good price, and if i do i'll keep you in mind.

[Geeto67]

as far as I know the dynoman GS manifolds fit the 1977-1979 GS750 carbs. I own a few sets of these carbs (I used to own a 77 and 78 GS) and the spacing is different from that of a honda rack, I also have a back in the day manifolds for adapting them (hard as a rock). The carb spacing is the same for 1973-1978-ish z1, kz900, and kz1000.

FYI, although they look like it, the bone stock GS and KZ carbs are not a true smooth bore. A smoothbore is where the slide moves all the way out of the inlet air stream, both the GS and kz carbs have a little lip of slide that hangs out into the stream. the real smoothbore carbs look externally almost identical save for a few subtle differences. However the kz and GS both use mukuni VM carbs which are an excellent carb.

The real advantage of these carbs to a stock motor cb750 is in the accelerator pump, which the 1977-78 cb750 carbs also had. The GS carbs tend enhance the cb750 head's flow shortcomings and you should really think about some porting to take advantage of the carbs, otherwise you are better off with your stock 77-78 carbs.

I am not 100% sure but I believe the kz650 carbs are spaced differently.

[Geeto67]

when you look into a smoothbore carb with the slide open it should look like this:

[Soos]

Shouldn't there be some warning when showing porn like that!!!??

 
NICE.

Can you measure the center to center distances of those kz650 carbs?
I will measure the center to center of mine for comparison if interested.
The easiest way would be to hook a tape measure on the outside of carb 1 and record the measurement of each carb edge to the #1 side of the rack.

l8r

[FunJimmy]

Can you measure the center to center distances of those kz650 carbs?

+1
I'm very interested in that too.

Thanks
FJ

[garretcb750]

The spacing on the carbs i have is aprox. 34mm between carburators 1/2 and 3/4. Spacing between 2/3 is approx. 56mm. Also when i open the throttle assembly the slides cannot be seen like the picture you posted. outlet O.D. is 39mm and inlet O.D. is 29mm going into the intake.  Does this mean i have a good set or actually smooth bores?

[mkramer1121]

See here for some info and jetting baseline settings:

http://www.z1enterprises.com/reference/z1-carb-guide.aspx

I believe if they are the VM29 smoothbores, regardless what bike, will work w/ the adapters sold on dynoman's website.  The only difference between the GS and KZ VM29 carbs are the slide cut out size. 

[garretcb750]

slide cut out size??? is it worth the swap? are they a much better carb. esp if i'm going to build a big bore/and cam motor?

[mkramer1121]

If you have the kawi ones, your fine.  its the gs ones that are the issue.  kawi ones are direct bolt on replacements.  if you're upgrading the engine, definently go with bigger and better carbs.  i had bought smoothbores to use on my project (which ive since sold to fund a home purchase) as they are great performing carbs and look better the the cr's.

[garretcb750]

they are indeed off a kawaski. currently i am running 29mm carbs on my 75' cb750f so there is little or no size difference. are these still a better carb? and by direct bolt on you mean with the rubber adapters sold by dynoman?

[FunJimmy]

The spacing on the carbs i have is aprox. 34mm between carburators 1/2 and 3/4. Spacing between 2/3 is approx. 56mm.

How can these measurments be helpfull. Is that simular to 75mm center to center of 1/2 and 3/4 with 100mm C to C for 2/3?
Center to center measurments would be much easier.

Thanks

[garretcb750]

ahh.. I was talking about the space separating the carburetors. Also, I measured the side that would go into the intake boots or mount to the engine. I am not able to measure them right away but I will double check for you when I can.

[mkramer1121]

they are indeed off a kawaski. currently i am running 29mm carbs on my 75' cb750f so there is little or no size difference. are these still a better carb? and by direct bolt on you mean with the rubber adapters sold by dynoman?

yes, direct bolt on with the adapters.  the spacing is different from a kz to a cb, thus the need for adapters.  Are you sure the 750F carbs are 29?  I thought they were 28.  Also, the smooth bores flow better then the stock 750 carbs.

See here:  http://www.satanicmechanic.org/carbs.shtml

[garretcb750]

great info..... thanks for your help. i might buy the adapters from dynoman and give them a try. from what I read on Z1 they don't seen to hard to set up for the CB. My carbs work ok but i am going to build a new motor with a big bore kit and cam and I am looking for ways to increase the performance. Stumbling upon 2 KZ's may have been my lucky day. I was going to sell them to a friend but now i think i might just ebay there parts and keep the carbs. from what i read on Z1 they are just 29mm smoothbores. Not the VM29 model you mentioned.

[FunJimmy]

ahh.. I was talking about the space separating the carburetors. Also, I measured the side that would go into the intake boots or mount to the engine. I am not able to measure them right away but I will double check for you when I can.

Thanks.

[mkramer1121]

great info..... thanks for your help. i might buy the adapters from dynoman and give them a try. from what I read on Z1 they don't seen to hard to set up for the CB. My carbs work ok but i am going to build a new motor with a big bore kit and cam and I am looking for ways to increase the performance. Stumbling upon 2 KZ's may have been my lucky day. I was going to sell them to a friend but now i think i might just ebay there parts and keep the carbs. from what i read on Z1 they are just 29mm smoothbores. Not the VM29 model you mentioned.

the only 29mm smoothbores are the vm ones (unless the stock ones were modified).  otherwise they are stock kz carbs (not smoothbore), which probably wouldn't be much difference from the stock cb carbs as they are the same diameter throat.  in your situation, i would save the money and properly set up my stock cb carbs properly (rejet, etc.).  in the future, i would save up the cash and buy a set of VM29 mikuni's, or a set of CR's.  Another option is using the DOHC CB750 carbs instead of the stock cb carbs as a performance increase.  Where the stock kz carbs come in handy is on a cb550 which had a smaller set of carbs.  you want to increase air/gas flow to the engine, and using a carb that is the same size as your current carb does not seem like it adds any additional benefit.  i am NOT an expert, but this is what i gathered when i researched a carb upgrade for my bike.

[garretcb750]

again.... good point and thanks. So, I won't get much of a performance increase from the KZ carbs, But a better performing carb. which would be ok but like you say it would be better investing my money in a bigger set of carbs esp. if i plan on installing a big bore kit and cam. I do have a 500 project on the go and if the turbo setup doesn't work out i could resort to using the kz carbs.