Another carb mystery!

[TopCatGr58]

Hey CrazCnuk,

Does sound like it's too lean, I remember a reply by PROM with a great explanation about this phenomena. Takes very little fuel to get it to idle, but when you crack the throttle open, lots more AIR gets drawn in, and without the proper amount of fuel to go with it, it dies!

IF they are very similar to the XS carbs and I think you said they were, then the pilot screws should provide the ability to get more fuel into the pilot circuit by unscrewing them out, and the pilot circuit does provide a fair amount of the fuel input before the rpm/engine gets going fast enough to start getting into the mains.

And you stated that the pilot/main towers share the fuel supply, and that would also lead me to think that the mains are woefully too small!? No telling what the PO did to/with them? Perhaps he tried jetting them according to year of bike and not actually model of carbs and put too small of mains in??
T.C.

[Crazcnuk]

I am leaning in that direction, too.

The problem is, I have been researching Suzukis that use these carbs, which is everything from GS400-GS1100, and the jetting is all over the place.

Each model uses widely varying air jet, pilot jet and main jet combinations. Also, they jump up main jet sizes for the smallest of changes, ie pods, K&N filters, and aftermarket pipes, far more than we do with the XS.

One interesting thing is they suggest DROPPING main jet size when you put a big bore kit on. They say the larger bore draws harder and so needs a smaller main...

Even in the GS1000-GS1100 some models use 107 mains and others are using 147.5 mains? All are what they call the BS34SS model carb. The were used in most suzukis from 1980 and newer.

Here are the specs for the closest model I can find, an '80 GS1000.

jet needle X-6
needle jet 5D50
pilot jet 40
main jet 115
pilot air jet 200

The only difference is the 200 Pilot air jet, the carbs here have 170s in them.

[Crazcnuk]

Z1 enterprises sells these carb kits for the 80-83 GS1100:


Carburetor Rebuild Kit GS1100 1980-83
KL18-2590

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These carb kits fit Suzuki GS1100 (4 kits required to service a set of carbs) Main Jet 107 and 115 Pilot Jet 40 and 45 Air Jet 160 and 170

$10.92

[petejw]

Craz, when i was mucking around with the kawa carbs had the same problem,
main jets were way 2 small, 90 were fitted, i went to 140 at the end.
Have you got any jets lying around from the early model xs carbs to experiment with?
Also might be handy investing in a set of tiny drill bits, makes life a lot easier and cheaper
and can be picked up from hobby/ hardware store.

[DGXSER]

Seems to me that you need to jet the carbs based upon the carb design when it comes to the how the pilot jets are fed, but you still need to customize the jet sizes to the bike.

meaning, if your feeding the pilot from the main, then you need the larger mains regardless of year of bike. And, you need the mains and pilots to be about the same size as the stock for the XS that matches the carb design as in 79 jetting for the covered pilot style as you have. Yes, I know that the sizes varied just a bit from year to year, but not as much as what you seem to have in them. JAT

[Crazcnuk]

I reset the float level, as they are set slightly different than yamaha. The bike still starts right up and idles fine. But if i give it any more than 1/8 throttle it will rev up then die.

Personally, I agree. I think that these should be jetted pretty much like a 79 carb. I could put in the same jets and needles, as an equiv 79 carb, and try it.

I dont have any of the early (big) jets, but i do have pilots and air jets.

i was hoping to hear back from the Suzuki site exactly what these carbs are off of. May make it a little more obvious why they are set up as they are.

An interesting question is what would happen if I just left out the rubber plug, as suggested earlier, and set them up like an 80 special?

[Rasputin]

Hey Craz. I have a set of 137.5 Mikuni jets, brand new in the package that I could express post to ya. If they work just replace em and if they dont just send em back. Seems to me it only took one day for express post last time I sent ya something. Just a thought as it would be cheap and easy to try. You would have to PM me your mail addy again as I deleted it.

[Crazcnuk]

That would be great. I really hate to start ordering stuff for these carbs, until I know they will work.

I can take the needles/jets, pilots and air jets out of my buggered set of XS carbs, for now. It was just the main jets I was stuck for, unless i stole them out of Derwat's SF!

[Rasputin]

Ok I got a set of 137.5's (from MikesXS) ready to go. I also have a set of 130's that were in my 79SF so I will send them as well just for sh%ts and giggles. I dont need the 130's back or replaced as they dont work on my bikes. SWMBO will have em in the post office first thing in the morning. I also have a set of 42.5 idle/air if you need em. Good luck.

[Crazcnuk]

I have 42.5's in both sets of XS carbs, I also have 2 sets of 45's.

I still need a #1 carb body to fix the one set. That's the only reason I am puttering with the Suzy carbs.

[petejw]

Hey Craz,
the only problem with leaving the caps of the pilot towers you would also have to block the tube that goes from the main jet tower to the pilot jet tower as it would suck up to much fuel.

[randy]

AHA!

This gives us one more option for fuel tees, Bikebandit shows it as a good Suzuki part #.

[Crazcnuk]

"the only problem with leaving the caps of the pilot towers you would also have to block the tube that goes from the main jet tower to the pilot jet tower as it would suck up to much fuel."

I think, if the plug is left out, that that passage won't do anything. The only reason gas gets sucked through it now, is that is the only passage for the pilot jet to draw through. If you take the rubber plug off, the pilot should draw through the big open hole right in front of it.

What we need to know is whether or not the pilot position was changed in the block-off-plug carbs?

[cywelchjr]

"the only problem with leaving the caps of the pilot towers you would also have to block the tube that goes from the main jet tower to the pilot jet tower as it would suck up to much fuel."

I think, if the plug is left out, that that passage won't do anything. The only reason gas gets sucked through it now, is that is the only passage for the pilot jet to draw through. If you take the rubber plug off, the pilot should draw through the big open hole right in front of it.

What we need to know is whether or not the pilot position was changed in the block-off-plug carbs?

That would depend on if it's before or after the main jet. If it's after, then you would likely have a problem, and I would guess it's after since the carbs with the cross passage use bigger mains, that implies that the fuel for the idle circuit goes through the mains, so leaving it open without the plug would leave a big open hole around the main jets.

[petejw]

Craz, i know what your saying i was figuring it would act
like the "H" piece on a dual exhaust system in that it would get
some flow thru it, give it a try and see what happens.