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VM26SS Carbs

  • Thread starter Thread starter mike1414
  • Start date Start date
I assume these are VM carbs. What really matters is the height of the fuel in the bowl. I used some clear line and taped it in the fuel drain bowl port. This will show you where your fuel level is when the bike is running. Disregard where the float tang is. If the bowl has too much fuel, lower the"fuel height". If you lower the float and the fuel height remains high, you have a problem with the float needle valve.
 
Well I got out there and gave it a shot, took the drain plug out and connected a piece of clear tube to the drain plug outlet and bent it upwards. Turned the pet cocky on prime and gas filled the clear tube only to about 1cm below the lip of the float bowl. That certainly doesn't seem like the bowl is filling too much. Did I do this incorrectly or was I on track for testing it correctly? Also noticed my petcock leaked a bit. Thoughts?
 
I also realized today that my needles do not have rubber tips on them; the tips are simply just metal, but they are not scarred or marked or anything. You can see a clear line where they plug the hole in the seat. Would having no rubber be causing an issue?
 
I had good height when the bike was off but the fuel level rose when it was running.

There's not supposed to be rubber on the float valve needles. If you can see or feel a line, you probably need to replace the needles.
 
Well guys, I have been trying to tinker with my floats at a variety of different heights, 22mm-27mm, and have played with the height of the tang as well to adjust the height of the actual needle in its seat. It seems as though no matter my float height, it still spills just as much gas and I still have the bogging down/crap throttle response within the first 1/8th of a turn. It doesn't seem as though my needle is worn, but I was going to purchase a new one anyways. Would there be reason that perhaps the needle/seat are just too large? Does anyone know the factory size and whether or not getting a smaller needle/seat would make a difference? I checked the carb vent, and it is free of debris (I read somewhere that debris in the vent could cause issue). What do you all think?
 
Both Kawasaki and Suzuki VM carbs used the idle adjust screw pointed down as on this set of carbs. Also, the pilot mixture screws purchased were never used on a Suzuki and the ones shown were used on Kawasaki VM26s 77/78 KZ1000 models. I coiuldn't tell for sure but did these carbs have air screws? Looked like someone tried drilling but didn't see an air screw and LAST... the pointy tip of a pilot mixture screw does fit up into a hole in engine side lower venturi in front of a hole that fuel flows from the pilot jet. The pilot mix screw is used to fine tune the pilot circuit in conjunction with the air screw/pilot jet on the Suzuki 26s. It might not be a bad idea to measure to see if these are actually 26s... they should measure about 26.5 - 26.7 mm or something like that on the venturi ID on the engine side.
 
You may never get these carbs right Mike. As GregT pointed out early in the thread these carbs may be from a foreign GS1000. At this point I'd look for a set from a regular US '78-'79 GS750.
 
The float valve needles and seats do come in different sizes. For some reason, I think the stock size is 1.5. If you look at them closely, I think it's written on them. From my experience, if you can feel any amount of ridge on the valve needles, they may by too worn. I bought these from Z1 and they fixed my issue. (Well that and tightening the one valve seat that I had forgotten to tighten. Doh!)

Are you still leaking on all four carbs? Did you try checking fuel height with the motor idling?
 
It seems that way, Greg. I was going to just order a new needle and seat because, at this point, why the hell not? I've been running it, trying to fine tune it to get it to com around, but I'm just leaking gas all around Jacksonville! If the needle/seat doesn't do it, then I may well go with a different set of carbs.

Thanks, Hannibal for the input. From what I've read online, it seems as though stock is a 2.2, but I may be referencing the slide-type 26's. It is only 4 that is noticeably leaking. 1 has a slight drop from the drain screw here and there, but typically that drop stays on the screw for a few days, drips, then another forms over the coming days. Carb #4 is the only troublesome carb. Even #3 with the machine screw for a drain plug is working well! I did in fact check (via the tubing method) with the motor idling, but in all honesty it didn't feel like I was doing it right (didn't have a really solid seal on my hose, but I seemed to make due). Shall I just go with the new seat as well, or better yet, how can I tell whether or not a new seat is needed (if ever)? Also, does it matter the size of the seat?

Geol I do have air screws and have tinkered with them to correct the throttle response, but they are of little value with the issue occurring in my carb #4. I knew we shared these carbs (in a certain fashion) with the Kawi's, but didn't know there were such differences. It seems, though, that even the fine tuning pilot mix screw would have little value in this instance, yeah?

I mean there really is nothing else that I could imagine this overflow issue to be outside of float heights. What has been the MOST perplexing is that it just came on relatively rapidly. The fact that it was running decently (not overflowing, only rough throttle) --> stopped working --> carbs were cleaned (FLOATS WEREN'T EVEN SLIGHTLY ADJUSTED) --> all of a sudden I have bogging in the first 1/8th throttle and overflow of the 4th.
 
The pilot hole on a Suzuki VM26 is of less diameter and thus the pilot mix screws are much sharper (and hence half of them are broken off when an owner seats them). The pilot mix screws on a Kaw seat into a larger diameter hole and are fatter where seated and thus don't break off as easily but will still break off if you over-tighten when seating. The Kaw screws are longer with a knurled head that sticks out from the well they screw into and the Suzuki screws are flat on the top and sit flush or below the surface of the well. A Kaw screw CAN NOT be adjusted so it meters fuel properly. Get Suzuki pilot fuel mixture screws.

mix_screws.jpg
 
Wow that's concerning. I bought these pilot screws from Z1 and they list them as fitting both Kawasaki and Suzuki. They look like the Kawa screws in your pic. Now that I think about it, I only used the springs with my original screws since my springs were missing.
 
I get my carb parts from SUDCO. They have a huge inventory of parts for Mikuni, Keihin, Hitachi and TK carbs.
 
Geol, I have actually gone through a set of those as well and I was unsuccessful with them. I really believe my carbs don't have pilot screws. Nonetheless, that wouldn't explain my leak from the overflow, correct. Also, I don't know if the more recent question was answered, if I alter the size of the needle and seat, would this relate to my overflow at all?

At this point, I'm also looking into just purchasing a new rack of carbs as well, not being able to ride is killing me. I noticed a fellow member has a set of BS32's from an 82 GS750 on here for sale; what carbs uld technically be compatible with my 79 GS750E? Take this set, for example. They are from a Kawasaki, but would they be compatible?

http://www.ebay.com/itm/kz-900-1000...17a651&pid=100338&rk=3&rkt=13&sd=321502981055
 
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Anyone? Could I fit the slide type 26mm on there? The Kawasaki 900 type 26mm? The needle and seat?
 
Not sure what you're asking about the Kawasaki carbs.

I imagine the bigger needle valves are for racing or highly modded applications. If you're motor is draining the bowls faster than the needle valve can refill them, you must be running the motor pretty hard.
 
I actually baby it quite a bit, don't throttle down very hard. The 4th bowl overflows, I don't think it necessarily drains dry.

In regards to the Kawi carbs, the older KZ900 seems to run the same (or similar) VM26SS carb - would there be any reason as to why these carbs wouldn't work in my Suzuki? Is the only real difference the location of the throttle stop? From what I've read and what it looks like, there doesn't seem to be any other difference. I would also assume I could just swap my carbs out for simple slide type 26mm Mikunis, yeah?
 
The Kawasaki VM26SC carbs from a KZ900 will work fine but will be far richer initial set up if the jetting is stock. In 77 they leaned the 26s a bit and if you get 78 or 78 1/2 VM26s, they are TOOOOOO lean. Just need to richen up the jetting a bit for the 78s or 78 1/2s. The main different will be the lack of a pilot mixture screw and adjusting the idle circuit air/fuel mix will only with the air screw and it is initially set at 1 3/8 turns out on a 76 VM26. Some folks look at the pilot mix screw on the Suzuki 26s as a benefit as it allows fine tuning but others look at the same screw as a pain in the... well pilot jet. Carb spacing is identical and the only operating difference will be your choke; Kaw VM carbs all have a choke lever/arm and if your current set has a cable to the choke, you will just need to remove the cable.

The float needle seat on VM carbs comes in sizes from 2.0mm to 2.5mm (to my limited knowledge) and obviously the larger allows more flow of fuel. I think that there are other things that limit flow that keep the seat from being the main jet, such as the jet needle/seat, main jet and fuel rail size. Most of the seats in kits are 2.0 as that is the most common application for factory VM carbs of any sort. If you bike were operated up higher in the rpm range a lot of the time and you had engine mods, perhaps larger seats would benefit (along with larger fuel pipes) but a stock bike, well, not much difference.
 
Exactly the explanation I was hoping for, Geol. Thank you for that. So, that being said, basically changing the needle and seat won't matter. I can't figure out for the life of me these carbs, so I may just purchase more and just tinker with these over time.

So an appropriate substitution could be the Kawi 26mm; could I plug in the slide-type VM26's and have those work? Why does my model have the VM26 "SS" as compared to the slide-type?
 
They are all VM26SS; ALL Suzuki 26s and ALL Kaw 26s except the 76/77 KZ900A and KZ900B and they were VM26SC. I HAVE NO IDEA WHY. They will all fit but you need to jet them according to your setup. In other words, the 76/77 VM26 from a KZ900; they are very rich from factory. Little rejet is needed for pods/pipe, etc. The 77 carbs from any KZ (900 or 1000) work but a main jet bump is needed for pods/pipe and the 78 and 78 1/2 need a bump in main jet and #20 pilot jets. The reason, just like Suzuki, is that the air jet size and slide cutaway change from year to year for reasons that are not intuitively obvious to an ignorant Texan. All can work fine if jetted correctly.

And your float needle seat? 2.0 or 2.3 makes almost no difference in a stock bike of any sort.
 
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