My carbs, my carbs! What did they do to my carbs?

[Mr.Midas]

Oh snap... I should have expected something like this, but I just kept assuming I still had the original carbs that hadn't been molested too much by previous idiots...

Some of you are familiar with my GS1000EC build thread of the bike I put together. Just as I'm beginning to think that I'm nearly done, I finally realize my carbs just don't seem to be what they should be...

What I thought was a minor difference from what the parts fiche listed on http://www.partshark.com/fiche_secti...1978&fveh=2146 and pictured in Paul Musser's VM Carburetor Rebuild Guide, may actually be missing pieces and/or the carbs aren't even GS carbs.

The pictures show the needles should have a spring and spacer below the e-clip and another spacer and a disc of some kind above. But all mine had/have were/are the clips, needles, and now the washer from the DJ III kit above the clip. Why would someone leave these parts out??? Are the spacers and upper disc made of metal, nylon, rubber??? How thick are they supposed to be???

And another thing that has had me wondering about whether or not these carbs are even GS carbs is the idle adjust screw position. It's above the carbs, not below like the factory manuals and parts fiches illustrate.

I'd like to punch the guy who messed with these and left out important parts.

I don't really care if these came from a KZ or whatever(It would be all the more fitting for the "Johnny Cash" theme the bike has going already), but it really ticks me off that some half-baked idiot couldn't even reassemble them properly beforehand... now I've got to delay a trip I had planned and hunt for stupid little parts.

I should be able to find suitable springs and spacers locally, but I have no idea where to begin with dimensions or material for the upper plate. Ordering these from Partshark would take a couple weeks and cost me over fifty bucks, and the top washer plate isn't even listed!!

This may also explain why the DJ III kit has made them run rich, even on the first clip setting with the DJ138 main. I wouldn't be surprised if the needle jet and pilot jet aren't the right sizes for GS1000's...


Any help to find suitable spacer, ring, spring, and upper disc dimensions/replacements would be very appreciated. I'm running out of available time for researching and testing solutions myself.


I'll post pics once I get them back apart and try to ID the needle and pilot jets...

[gearhead13]

I didnt know they made a DJ kit for VM carbs. You already have adjustable needles, dont you?
If it were me I would try to find a bike salvage yard nearby, quite a few models of vm carb part would probably work, and scour ebay, maybe a member here has a spare set of parts carbs??

[Don-lo]

If you have a vacuum nipple on carb #3, then they are GS carbs, probably 750s. Bike Bandit doesn't show any carbs for the '77 750 (lol), but for the '78 750 it shows 2 different carb schematics, and the second set of carbs have different slides that don't have the springs/plastic spacers.

[Mr.Midas]

Hmmmm... I see the idle adjuster is on the top side too. If these are 750 carbs how do they compare flow-wise to 1000 vm carbs? What really puzzles me is why it seems the pilot jet is running on the rich side(mixture screws are barely 1/2 turn out, and the motor will almost keep running with them turned in all the way.)

I assumed that in order to have a spring under and spacer washers on either side of the e-clip, there would need to be a pocket/counterbore in the top of the slide, but no such pocket exists in these slides. Just a slight recess for the e-clip. Maybe I'm not missing those parts after all.


I was planning to revert to the fatter adjustable needles that came in the carb to see if that would lean the mid range enough to take the bike up to where I'll be working/staying a few weeks. Once I'm there, I'll have more time to finish dialing the carbs in(probably smaller pilots, and definitely smaller mains if I want to go back to the DJ needles). I won't need the bike for daily transportation and I have a buddy who will let me use his tools & shop if need be.

I would have loved to have been able to start with the stock jetting to begin with, but two of the main jets(mikuni 100's I think.) were already missing. Most of my research led me to believe it needed a whole DJ III kit, but now that I know a little more, I probably would have been fine with some mikuni 120-125 mains and the stock needles.

[Mr.Midas]

Okay. I guess this thread should be renamed to, "Didn't know my GS1000EC has GS750 Carbs.... Now what?"


The ID #'s are: 45020




Before pulling the carbs again I decided to check and eliminate some more unknown variables... I just checked the fuel levels with the bike running. All line up and match the level pictured(I had already carefully set them to 24mm previously) <---- This is too bad because I'm guessing these 750 carbs should be set @ 25-27mm Perhaps this 2mm higher fuel level difference is the reason I had to turn my pilots in so far from base settings and set the needles to the leanest position?

Next items to address where the low-ohm vt750 coils I had running with the Dyna-S ignition and possibly causing inconsistent spark(which could eventually foul the plugs/make the carbs appear rich). The 1.2 ohm $4 ballast resistors I ordered from the local parts store brought the total resistance for each coil up to 3.5ohms accounting for meter lead resistance, so now that possible problem has been eliminated.

While checking fuel levels and running off the remote fuel supply, the idle was very consistent, and it revs all the way to redline without major hesitation; although, while holding it at 5-6000rpm, the motor/intake doesn't seem to sound as smooth as it does above or below that range. I guess I'll double check the carb syncs, set the floats back to 25.5-26 mm, install fresh plugs, and do some high and mid range chops to verify the mixture problem still belongs to the needle, but I'm almost certain the needle needs to go leaner(already at the top slot). That's when the old needles go back in, and I repeat the whole rich/lean testing process again.


According to the parts fiches, the 78 GS1000 & GS750 vm carbs should have the same needle jets and pilot jets(unless the 22.5 pilots partshark.com also lists have been installed in the 750 carbs), but different size mains and needles.

By all indications the mixture is reasonably close to where it needs to be. With fresh plugs the bike runs right up through to redline fairly smooth(I know VM carbs don't like to be snapped open, but these could probably respond just a hair better.

Wouldn't it be something if just resetting the float height back to the 750's level cures the problems I'm having with apparent richness/plug fouling...

[Mr.Midas]

After changing float level back to 26mm and synching it's running much better, and was *almost* able to make it through the acceleration mode rich test. Just a couple sputters around 5000-7000rpm before pulling hard to redline.


Pulling the plugs after 20miles revealed something interesting... The #2-3 plugs show signs of slight leanness(very little deposits at all/can still see the white of the insulator), while the outer #1-4 plugs appear to be on the low side of richness(very thin black/very dark brown carbon coating).


I'm going to blame this on my APE pod filters and the looser work-pants I was wearing. My knees rest on the gas tank right above the carbs, allowing my loose pants to basically smother the outside half of the pod filters which are already probably anemic to begin with.


Still wishing I hadn't been outbid on that set of K&N's oh so many months ago. The extra capacity of the ovals would definitely make them harder to smother with loose clothing.


Time to try a couple runs while holding my legs out away from the filters...

[Don-lo]

Good to hear you are making progress. I've found that the 750 carbs can work, but they are more finicky. Did you paint the carbs?

[Big T]

Okay, how did thread veer off into a 750/1000 carb thing?

Both bikes use the exact same VM 26SS carbs, with different jetting specs

Stop using the parts fiche and get out your factory service manual. You did download the free one from BassCliff's site, right?

You mention the idle adjuster is on the top? 1000s have them on the bottom, in the center

Give us some more pics of your carbs

What jets are you running?

What needles? and what clip?

[Don-lo]

Big T, they were not exactly the same. Some early 750s had older style carbs, distinguished by the slides that would capture the needle e-clip directly rather than the spring/big spacer/small spacer combo. See here:

http://www.bikebandit.com/1978-suzuki-gs750c/o/m6101#sch280078

It is my experience that these carbs are more difficult to tune precisely. I'm not sure if it was the combination of parts in there or if the later version actually improved the midrange mixing. I had a 750 that would run great but foul plugs. When I lowered the needle one position, it would immediately run lean and bog badly in midrange. Another 750 I owned would run great with one exhaust, but ran terrible with another. I never had any such problems with any of the GS1000 carbs.

[Mr.Midas]

Sorry it took me so long to get back online... The carbs are now running at a point that after an 800 mile trip have yet to foul the plugs out; although, I still think it's running rich. It averaged 30mpg on the highway cruising 70-80 mph @ 4000-5000 rpm in 5th gear 90% of the time. Still bogs in the mid-range if I try accelerating spiritedly or go up decent hills.(At higher speeds it's not as noticeable and handled the VA-WV mountains/country roads better than I expected)


The carbs have the Dynojet stage 3, DJ3304, kit installed /w DJ138 mains & needles set to #1 clip position with washer on top. Stock mikuni #15 pilots, mixture screws ~1/2 turns out, and air screws ~2 1/2 turns out

Pic of the rack after reassembly:



They were painted with VHT caliper paint after being dipped in Berryman's Chem-dip and thoroughly cleaned(afterwards, I noticed that the plastic slide guides where loose in three of the carbs, so I resealed them all with plastic epoxy from the outside)


There are more shops and even 1-2 dyno's close by to where I'm staying in NJ now for a couple weeks, so acquiring some of their services to help dial in the best setup will probably be worth it. I know I can't assume where the problem lies, or blindly test/change multiple things at the same time.

Before changing anything, it would probably be best to check the WOT mixture on a dyno. The power output/acceleration feels really good above 7000rpm on up into redline, but that isn't enough to tell me what exactly the mixture is doing. I don't think I can trust plug readings because of how far I need to drive(dirtying the plugs in the process) to get to a clear stretch of road to test WOT(not to mention the attention I'd likely get from the authorities... and the extremely stupid deer that are everywhere around here as well).

[Big T]

Fuel screws to one full turn

Raise the needles 1-2 positions

My stock 1000 pulls hard from below 4000 rpm and got 45 mpg going up/down Mt St Helens a few weekends ago (100-4,000' elevation change)

Isn't it fun when you ry to add HP, but it goes the other way??