Another carb mystery!

[Crazcnuk]

They came off of an 80 XS1100G, so the do fit. That is why the confusion, I assumed they were early 80 Yamaha Mikunis.

They are close enough to pass themseleves off as Yamaha, but there are a few slight differences.

1) Diaphragm springs are much smaller.
2) Lids have smaller guide for the smaller springs
3) no detent balls/springs on the choke rod, but an extra spring
4)Same size slides, but different circlip system for needle retention.
5) shorter, fatter needles
6) X-6 tubes
7) Float valve retention clip has an arm to limit float drop (no clips on the float needle)
8) Float bowl drain screws have phillips screwdriver capability, and smaller threads.


Other than that they are the same BS34's we all know and love, sort of.

From my reading, it looks like Suzuki used these for most (all?) GS models after 1980. They are, however, tuned for each specific bike. So, in order to get close on the tuning I need to find the specs for these carbs if they were on a GS1000 or preferably a GS1100.

From there it would be the usual trial amd error.

I don't know if I could just set them up as using all the XS11 parts for this particular style of carb (ie: early 80's transition)

I have 42.5 pilots, 185 air, and stock needle/tube sets, but I would have to order 137.5 (and larger) mains.

[Crazcnuk]

The carb kits for a GS1100 80-83 comes with:

107 and 115 main jets
40 and 45 pilot jets
160 and170 air jets

So these, with 115, 40 and 170 are probably right in the ballpark.

[Crazcnuk]

So....

Any thoughts on whether I should rejet these ala '79 XS11 style or GS11 style?

Or is it not worth playing with?

[tarzan]

I think I would try them as is,then go from there

[petejw]

I'd put what you had back in,
ride the bike and go from there.

[Crazcnuk]

I was leaning that way, as well. Curious as to how the smaller jetting makes for more power.

Also the smaller diaphragm springs may make for wuicker throttle response.

I assume the GS revs higher than the XS?

[petejw]

I'm interested 2 see how it runs with that set up also,
its not to far off from the stock settings of the xs,
the smaller air jets make for a richer pilot jet.
check out the factorypro site, it has a good method for checking if you have the correct air jet, when riding the bike.

[Crazcnuk]

Yes, but it has smaller air jet and smaller pilot jet, too.

The actual main is slightly larger 115 instead of 110, for the 1980 G, but since these have siamesed pilot/main, one would think they should use 137.5s, like the 79 XS.

I would assume what makes the difference are the 'fat' needle/jet combo.

The suzuki carbs also have 4 holes in the air filter bell, instead of 3 like the xs.

[Crazcnuk]

Put these carbs back together. Used new main jets, since I had some, the rest I just cleaned and put back together.

The choke rail is odd, it has no provision for ball detents, so I don't know how it is supposed to stay when you put the choke on. It has a spring on each choke so it's natural tendency is to pull the choke off.

Now to talk Derwat into 'modelling' them on his special...

[petejw]

Craz,
have you got any pics of the carbs?
usually if theres no detent to hold the choke open,
a cable is used, is it possible the choke is operated
with a cable?

[Crazcnuk]

No, it has the same type lever as ours.

According to the picture on thegsresources.com

http://www.thegsresources.com/images...%20removed.jpg

There is a spring and an extra large clamp (left side of the picture) but with these, that spring is not there, and all 4 rod clamps are the same.

[Crazcnuk]

Ok, I think the PO put the XS choke assy on the Suzy carbs. This goes with the fact that the holes where the XS lever mounts to carb #1 were not tapped. The PO had the lever tacked on with a couple of wood screws.

So the Suz probably had a cable choke.

I put the carbs on the SG today, and they idle great, although the vacuum adv rattles pretty good at idle.

However, If I give it any throttle it bogs, any more and it dies. I can get it to rev up, once, every so often, but then it bogs.

The only way I can get it to rev a bit is to pull on the choke.

These carbs only have a single fuel inlet, in the center, but I think it could be set up to use our dual feed without too much difficulty.

[cywelchjr]

Ok, I think the PO put the XS choke assy on the Suzy carbs. This goes with the fact that the holes where the XS lever mounts to carb #1 were not tapped. The PO had the lever tacked on with a couple of wood screws.

So the Suz probably had a cable choke.

I put the carbs on the SG today, and they idle great, although the vacuum adv rattles pretty good at idle.

However, If I give it any throttle it bogs, any more and it dies. I can get it to rev up, once, every so often, but then it bogs.

The only way I can get it to rev a bit is to pull on the choke.

These carbs only have a single fuel inlet, in the center, but I think it could be set up to use our dual feed without too much difficulty.

It seems like your going to a lot of effort to make carbs not even intended for an XS work with it.

Of course I understand it hard to actually find the right carbs, but with the work your having to go to, and the lack of success. Then again, maybe with the plug in there your really need to bigger jets for it to work off idle? Either that or maybe leave the plugs out of the idle circuit and see what happens?

[Crazcnuk]

I haven't actually done much, yet. I've done more searching on the internet than real work.

So far I've just cleaned them, and tried them out.

We decided I should just try them as is, to see what they do.

Near as I can tell, these are probably from a GS1000. They seem to be stock configured but I haven't been able to find the exact model # (49150) on these carbs.

[Crazcnuk]

What? None of our gurus have any insight to what it means when a carb idles fine, but dies as soon as you give it ANY throttle?

I am not worried about this, I think of it as an interesting puzzle to solve.