Author Topic: mystery carbs on my 750 supersport (Read 7384 times)

freestyleroll · « **on:** June 09, 2011, 06:56:18 PM »

i've searched for hours already and turned up nothing on these carbs. i recently bought a sohc cb750 supersport in non running condition. it's been layed down in the past, and my theory is that a previous owner bought parts and put it back together... problem is, the carbs are not correct for this bike. it's a 76 supersport, but it has constant velocity carbs on it. i'm having trouble nailing down what bike these carbs are from. long story short, i bought the bike in nearly stock condition... since then i got it running pretty good, and stripped/chopped it a bit. i've seen similar models of carbs on cb650 and nighthawk models, but they still don't match up 100%. i'd like to buy some new parts for the carbs, but since i dont know what model bike they came from, i cant really order parts. there are no stamped numbers or casting marks, except for "mikuni kogyo" stamped on one side, and "made in japan" on the other side... if more pics would be helpful just specify what you want, any help would be greatly appreciated.

there are some faint printed numbers on the outside carbs, in picture # 3 the screwdriver tip is pointed at the numbers.... 45110 and C093

here are pics of the carbs and bike.

freestyleroll · « **Reply #1 on:** June 09, 2011, 06:58:22 PM »

some more pics of the carbs...

Retro Rocket · « **Reply #2 on:** June 09, 2011, 07:21:54 PM »

I don't think they are off a Honda, Honda usually uses Keihin carbs, those are Mikuni's....

Trav-i · « **Reply #3 on:** June 09, 2011, 07:26:32 PM »

They look like GSX-R carbs to me.

Retro Rocket · « **Reply #4 on:** June 09, 2011, 07:31:51 PM »

Quote from: Trav-i on June 09, 2011, 07:26:32 PM

They look like GSX-R carbs to me.

Maybe but early GSXR carbs were flat slide , they look like GPX or GPZ 600 {ninja} carbs....I would try searching 80's model Kawasaki's or similar for a match.

Patrick · « **Reply #5 on:** June 09, 2011, 07:38:30 PM »

Those look just like the carbs on my '79 Yamaha XS1100. Do they have any markings on them, like BS-34 or BS-38?

On closer inspection, the air screws on them look more like BS-38, which were on 80 and 81 XS1100s.

Patrick

freestyleroll · « **Reply #6 on:** June 09, 2011, 08:49:17 PM »

yeah i was starting to think they weren't off a honda. the only markings are "45110" and "C093" printed on each side. i'll search kawasakis and see if they match.

MoMo · « **Reply #7 on:** June 10, 2011, 06:15:20 AM »

Look like Yamaha Maxim carbs from the 550 to 750 range. I had two in for repair a couple years ago and I think your carbs were similar...Larry

c(b)hris · « **Reply #8 on:** June 10, 2011, 06:48:32 AM »

When I google "mikuni k03y0" I get hits for a gs550.

http://www.sella.co.nz/motoring/motorcycles-scooters/parts-for-sale/fuel-tanks/828vyw/

johnrdupree · « **Reply #9 on:** June 10, 2011, 07:40:59 AM »

Maybe from a early 80's GS750? The Motogrid diagram is remarkably similar, right down to the wire spring thingy on the bottom:

http://www.motogrid.com/pages/OemParts?aribrand=HOM#/Suzuki/GS750E_%281981%29/CARBURETOR/02800002/5602800011

Can you get a better pic of the numbers on the side?

Chris, it's not "mikuni k03y0", it's Mikuni Kogyo, the full name of the company.

freestyleroll · « **Reply #10 on:** June 10, 2011, 11:15:11 AM »

the numbers on the side barely show up in pics, thats why the one pic has a screwdriver pointed at the location... the numbers are very faint, not casted or stamped into the metal... they appear to be printed on like this. 45110
C093

from what i've seen so far, they seem to match up the best with mid eighties maxim xj700 carbs... i cant seem to find a set that has the exact same location for the vacuum ports on the carb mouth, and the tops are still different. cant find a single set with "mikuni kogyo" cast in the tops.

freestyleroll · « **Reply #11 on:** June 10, 2011, 11:18:57 AM »

as for the xs1100 carbs, there are four ports on the front of the carbs instead of two on mine.

c(b)hris · « **Reply #12 on:** June 10, 2011, 11:28:29 AM »

Quote from: johnrdupree on June 10, 2011, 07:40:59 AM

Chris, it's not "mikuni k03y0", it's Mikuni Kogyo, the full name of the company.

whoops.

freestyleroll · « **Reply #13 on:** June 10, 2011, 12:17:49 PM »

@ chris... the picture you posted is almost spot on, except for the writing on the tops. the shape of the cv port and the placement of the vacuum ports on the mouth of the carbs appears to be the same. also, those carbs only have two vent hoses, just like mine. AND there appears to be a small vacuum line coming off the second carb from the left... exactly like mine also. choke linkage. also appears to be the same. i think maybe there are some differences in the brackets that hold all four together... the diagram that "johndupree" posted looks like the brackets are shaped the same as mine.

freestyleroll · « **Reply #14 on:** June 10, 2011, 12:20:33 PM »

GS 850 carbs are looking suuuuper close too

freestyleroll · « **Reply #15 on:** June 10, 2011, 12:28:42 PM »

pics of 80' to 83' suzuki GS 850 carbs i found, they look spot on...

Redman · « **Reply #16 on:** June 10, 2011, 12:31:04 PM »

I have a 1981 GS850 and they are identical.

freestyleroll · « **Reply #17 on:** June 10, 2011, 12:41:14 PM »

hey redman, u have the bike those carbs came from? i've got a question you might be able to help me with... in the picture from the above post, look under the choke linkage on the second carb to the right. theres a vacuum port pointing up.... i'd assume possibly a hose goes from there to the airbox?

Patrick · « **Reply #18 on:** June 10, 2011, 02:28:43 PM »

That vacuum port is on the body of the No. 2 carb to feed the vacuum advance. To use the carbs on a CB750, which has a mechanical advance, you want to cap that port.

It would be interesting to see how you could do a running synch on a 750. The ports that are used for synching beyond bench synching are in the carb manifolds (rubber carb holders). You bench synch them by setting the butterflies to the same gap at the carb throat. You should find three little holes in the throat of the carb right about where the butterfly closes. Those come from the slow jet and control your low end throttle. You can get the synch real close by setting the butterfly right in the middle of the outermost of those holes.

Also, the jetted port on the mouth of the carb is not a vacuum port. It is an air jet that feeds the enricher circuit.

Patrick

freestyleroll · « **Reply #19 on:** June 10, 2011, 02:34:19 PM »

yeah air jets, i have a bad habit of calling them vacuum ports, i dunno why. and the vacuum advance tube you are referring to was plugged when i got the bike, so i just left it that way. i wasn't sure wether it should be plugged or not, so that answers my question... thanks man. and i saw the three little holes you are talking about, but the butterflies are covering the outermost holes too... so i should adjust the butterflies to sit directly in the middle of that outermost hole?

Patrick · « **Reply #20 on:** June 10, 2011, 02:44:16 PM »

Yeah, try to split that hole exactly the same with all four butterflies. That will get you very, very close on the synch, assuming your valves also are set evenly.

If you have issues with your idle or you low end throttle, pull the slow jet and spare carb cleaner into the slow jet hole until it bubbles up through all three of those three little hoses.

And, if you decide the clean the carbs, DO NOT immerse them in caustic carb cleaner. Use only spare cleaner or Yamaha carb cleaner (which does not hurt rubber). There are rubber butterfly seals at the base of the shaft the butterlflies turn on. Caustic cleaner will kill those seals. and you wil develop air leaks and very lean running conditions(DAMHIK!). Those seals are also really difficult to change.

BTW, if you decide you want to keep using those carbs and you want to clean or rebuild them, let me know. I can give you a link to a very good online tutorial on how to tear them down and clean them, as well as explain how they work. They are more complex than CB750 carbs and have a lot more circuits that have to be clean for them to work properly.

They are high performance carbs, but you can make them even more reactive by switching in a stronger spring to the diaphram.

Patrick

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Author Topic: mystery carbs on my 750 supersport (Read 7384 times)