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Performance gain of Mikuni 28mm vs 26mm?

KEITH KRAUSE

KEITH KRAUSE

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I know the 28mm are not as nice as the 29 smoothbores, but do you think the performance gain would be worth the re-jetting fun?
My '79 GS1000 has a 1085 kit, K&N ovals, V&H pipe, and a Dynojet kit for my stock 26mm carbs. The bike runs really strong.
Does anyone here have experience with using the 28mm on a bike that had 26mm? Was the performance gain worth the work? Any info greatly appreciated including how fuel mileage was effected, etc.
Also, the 28mm were for bikes sold outside the U.S., correct?
Anyone have the spec's for the 28mm so I can compare to the 26mm? Thanks! :)
 
Hi Keith,
To be honest I wouldn't spend time on 28 or 29mm's, CV's or not. If you want affordable powergain, switch to 36mm slingshot carbs off an oilcooled GSXR750. If setup right, they are fantastic on all big GS's. If your bike is powerful and smooth already, I would leave it.

Good luck! Marco.
 
The 28mm Mikunis flow more gas/air than the 26mm and if you have the engine, they will provide a nice performance gain. I suggest you look into using Kawasaki VM28 carbs if you want to go that way as they are far easier to find. The main difference is that the choke lever is on the side of the assembly that actuates the choke plungers. No matter what type carb you get, keep in mind that rejetting MUST be relative to the original jets that came in THAT carburetor assembly. There were about a dozen Kawasaki VM28 variations and main jets varied from 105 to 125 based on the starter jet, jet needle and needle jet combination and whether the carburetor had an accellerator pump.
 
Thanks for the replies. :)
I kind of wonder if I'm opening a can of worms here. As wiredgeorge said, I'm aware of the jetting variations and you could spend a lot of time getting them tuned. I'll most likely not try them.
For anyone not knowing, there's a set of NOS 28mm on E-bay now. $76 so far, reserve not met. I'm too dumb to provide a link. I just type in "NOS Suzuki GS 1000" and there they are. Good luck.
 
KEITH KRAUSE said:
Thanks for the replies. :)
I kind of wonder if I'm opening a can of worms here. As wiredgeorge said, I'm aware of the jetting variations and you could spend a lot of time getting them tuned. I'll most likely not try them.
For anyone not knowing, there's a set of NOS 28mm on E-bay now. $76 so far, reserve not met. I'm too dumb to provide a link. I just type in "NOS Suzuki GS 1000" and there they are. Good luck.
Click to expand...

Linky :D http://cgi.ebay.com/ebaymotors/ws/e...ry=35595&item=2493809808&rd=1&ssPageName=WDVW
 
robinjo said:
KEITH KRAUSE said:
Thanks for the replies. :)
I kind of wonder if I'm opening a can of worms here. As wiredgeorge said, I'm aware of the jetting variations and you could spend a lot of time getting them tuned. I'll most likely not try them.
For anyone not knowing, there's a set of NOS 28mm on E-bay now. $76 so far, reserve not met. I'm too dumb to provide a link. I just type in "NOS Suzuki GS 1000" and there they are. Good luck.
Click to expand...

Linky :D http://cgi.ebay.com/ebaymotors/ws/e...ry=35595&item=2493809808&rd=1&ssPageName=WDVW
Click to expand...
SHOW-OFF! :lol:
 
I have used the Kawa 28mm carbs for many years. They do provide for a fatter power curve all round if you have the pipe and engine work to take advantage of the flow. I get better fuel economy than when the bike was bog standard! The difference won't be arm tearing power, but it will let the beast off the leash a bit more. The advantage is that they fit in the standard manifolds.
 
I think it would be well worth the trouble if you have access to a good set of 28's. This was done a lot, way back when & I don't remember it being a that big of a deal. The 28's would help the stock GS 1000's and would help yours, with your mods even more.
 
Quit trying to talk me into it! :lol:
Anyone have the spec's on these carbs, so I can compare the internals with standard 26's?
wiredgeorge or anyone, why would there be so many jetting variations with these carbs? They were originally made for BOTH Suzuki and Kawasaki's? These were never intended for U.S. models, correct?
 
I have the internal specs on most of the Kawasaki VM26 and VM28 variations but they are hard to decipher without some knowledge of the codes on jet needles and needle jets and sundry other seemingly minor internal difference affect the operation of the carburetor assembly. Mikuni made literally dozens of different length jet needles with many different taper characteristics and these are matched to the needle jet. This forms the basic flow characteristic for the carburetor. The main and pilot jets must be matched. They spec'd out the carburetor internals for Mikuni in order to change the flow characteristics they wanted to achieve as the easiest way to affect the performance characteristic they were looking for. They typically went for either low end performance, all around performance or more performance at the top. This is why you can see a VM28 Kawasaki carb with an OEM 105 main jet or an OEM 125 main jet. With either, if you retain the OEM small internals, you will need to base rejetting from the original... in other words, if you have internal mods, pods and freeflowing aftermarket pipes, and you were using the VM28 with 105 main jet, you would base rejetting on the 105 main jet.

I have a large assortment of the small internal parts and can modify the characteristics of any VM series carb but typically I don't care to do this. If someone wanted to drag race, I could provide more gas on the top end by swapping needles, needle jets and main jets but this would seriously affect driveability in the lower speed ranges. Most of the combos Kawasaki chose might favor one range of operation or the other but not seriously affect driveability. BTW: All sets of carbs I sell are not only cleaned and rebuilt but also tuned and tested on a motorcycle and ready to ride. I will typically tune/test with OEM jetting using a factory airbox/OEM style pipes and then rejet for higher performance applications. The jetting for Mikuni VM round slide type carbs can be predicted pretty accurately based on performance modifications so this method works pretty well for setting up dialed in carburetors.
 
Thanks for the info. :)
You know, the carbs I'd really like to try someday are the 29 smoothbores. Parts availability is what scares me off, besides the tinkering.
I was just wondering since you have a lot of experience with carbs, if you have any info on "pre-jetted" 29 smoothbores? Back in '84, Motorcyclist magazine built a '79 GS1000 project bike. The mod's were a V&H pipe, 1085 pistons, K&N ovals and the smoothbores. You could order these pre-jetted carbs made specifically for these mod's from Vance & Hines.
Last year I had no luck contacting V&H about the jetting spec's for these carbs. Sudco couldn't help me either, except to help scare me off about how difficult it's getting to find a good set or get good parts. I'm sure someone, somewhere, has this jetting info.
Any ideas? :)
 
here is some jetting info for 29mm

expvm29.gif


img doesn't work here is the link
http://www.sudco.com/Diagrams323728/expvm29.gif


and here is a tuning guide for them

http://www.grimp.net/ryan/FC_Mikuni_1979.1988_carb_Guide.pdf
right click "save target as" above link
10 meg file 56k beware


-ryan
 
Keith, of course I haven't had luck out of my CV's yet but have you considered trying these off of a later model bike? I have a old KZ1000 that I would like to put the CV's if I can ever make the 33 smoothbores work on my 1150. I would think that these would be the smoothest power you could get for your bike, just a thought. Mike J
 
mike J said:
Keith, of course I haven't had luck out of my CV's yet but have you considered trying these off of a later model bike? I have a old KZ1000 that I would like to put the CV's if I can ever make the 33 smoothbores work on my 1150. I would think that these would be the smoothest power you could get for your bike, just a thought. Mike J
Click to expand...
CV carbs would require a later model head. They won't just bolt on. My manifolds and K&N's would be useless too. I actually prefer the VM carbs to the CV's.
 
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