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77/79 GS750 VM26 carbs, spacers missing from needle assembly???

Chuck78

Chuck78

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Past Site Supporter
So I have been soaking my carbs for days and days, and have new larger jets to install, and was going to raise the needles one notch. I just went to put them back together, and as I pulled the slides apart to raise the needles, I was shocked that there weren't the two little rubbery plastic thin and thicker spacers on either side of the clip that retains the needle as I had been accustomed to on the GS550 VM22's I've worked on. I have a spare junk set of VM22's, so I think I will pull those apart and rob these parts from them, but I was wondering which one went where, thicker on top, thinner on bottom? with the c-clip in the middle? in the VM carb rebuild pdf, the photo shows a spring in there also. it does not show the assembly order, however, as all the parts are disassembled and just sitting there in the photo. I assume this spring goes under??? Or over??? Maybe the disassembly on the 22's will spell it all out, but the VM rebuild guide said it was of a 78 GS750, so I assume these carbs (I think engine is a 79 and it has 79 sized #15 pilot jets in it now) are the same.

assembly order, and any other comments???
 
This was a shocker to me, as the factory paint marks (tamper-proofing/loctite) on the pilot fuel screws and carb synch adjustment studs/nuts was still intact from the 70's! where did these things go!???!!!

With spacers and maybe the spring missing from under the clip, this thing must have been running soooooo darn lean... ouch! I thought the main was just too small for my unrestricted 4-1 exhaust mod, max power was at 3/4 throttle... K&N filters and rejet will probably give me an insane amount of additional power...wow. Hope my exhaust valves aren't burnt from running a few thousand miles lean!!!

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VM 26s that I have taken apart for all my bikes have no springs. Nor did the 78 750s VM 26s.

Needles went in, then the linkages were bolted (screwed) on. Be sure to put them on the right way too...look for the air escape hole to be there when you get set to put in the screws.
 
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1978 GS750EC is what the one in the photo I posted was off of.

I tore apart the VM22's and they have an obvious large recess in the slide where the spring sits, and mine don't.
Mine, however, have no thin plastic washers above or below the clip on the needle as in the photo I posted. The schematic on the link you guys posted shows exactly what I saw when I pulled mine apart, no spacers whatsoever, slide/needle/clip/linkage. no thin spacer under, no fiber spacer above. Do some spring-less models have these little plastic washers?
 
it seems as if there should be some sort of cushion to keep the needle from rattling around in there at the very least, unless this c-clip is the exact same thickness as the slight recess in the top of the slide. hmmm...???

I now have an extra set of needles to play around with now however. The 550's carbs have 5DL35 needles. I was going to try some 5DL36 needles at some point, and wonder what the difference is between the two. the stock GS750 needles are still 5F21's, which are much thicker than the 5DL35's at the tip. Seems the GS550, 850, and 1000 need way more fuel delivery at 1/2 to 7/8 throttle.

FINALLY!! I found some sort of document on Mikuni needle taper specs! Not in english, but oh well... I can figure out what it says, gotta love latin-based languages. http://www.docstoc.com/?doc_id=147891695&download=1
 
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The spring in conjunction with the little dimple on the plate cocks the needle to one side so it doesn't rattle and wear out. The early GS 750 VM26es didn't have it, I can't remember now if all of the VM22s did or if the early ones did not.
 
So now I am confused..are the parts you posted in the thumbnail what DID come out of the carbs your working on? ( for the 750??) If so then the order is as follows...thin washer below the clip and insert into the slide. Thick washer on top of the needle, then the spring. put on the linkage.

If you have "regular" 750 VM26s then there are NO fiber washers involved. Clip in center groove and insert. put on the linkage.

The needle top goes in a little hole in the linkage plate thing and pinches the clip to keep it from wobbling.


You may have a newer set that was made with the washers and springs??
 
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chuck hahn said:
So now I am confused..are the parts you posted in the thumbnail what DID come out of the carbs your working on?
Click to expand...
Nope, he ripped the photo out of the VM overhaul guide. Ain't a picture of his carbs. Had me going for a minute as well.
 
tkent02 said:
The spring in conjunction with the little dimple on the plate cocks the needle to one side so it doesn't rattle and wear out. The early GS 750 VM26es didn't have it, I can't remember now if all of the VM22s did or if the early ones did not.
Click to expand...

The 77 GS550 VM22's here have what is in the photo. The spare unknown junk parts VM22's here that look identical have what is in the photo.

My 1977??? GS750 has no spring, no spacers. Only needle and clip. It does seem to be a 1979 engine number and probably '79 carbs due to #15 pilot jet in them, main jet must have been upsized to 105 with the 4-1 exhaust and oversized pistons as stock 77 is 105 stock 78-9 is likely to be 100 if not 97.5 in some markets)

The photo I posted is from the VM carb rebuild tutorial pdf file from a 78 GS750EC. I just copied it from the downloadable pdf on the GSR main site.
 
Sorry for the confusion, should have made it a little more clear that the photo was NOT my carbs, mentioned it was from the carb rebuild tutorial pdf.

Well, at least I now know that I have a set of 5DL35 needles to play with on the GS750! It looks as if the 5DL35 and 5DL36 are the same specs all around from the taper dimensions on http://www.docstoc.com/docs/147891695/Mikuni_Nadelnxls---mintelonline

The 5F21 that was stock is a much fatter diameter (leaner mixture) needle...

The taper on the 5F21 starts 2.7mm further down than the 5DL35/36's. The taper on the 5F21 goes from 2.515mm to 1.688mm, the 5DL35/36 goes from 2.522mm to 2.438mm, and then gradually to 0.878mm. BIG difference. This seems like a MASSIVE fattening of the midrange. I think that if I could pull off running that needle before I do the bigger big bore 920cc setup, I'd have to have the clip on the middle position for sure, not any richer. May need to start another thread, or just try the darn things after a baseline run with the stock needles raised one notch.

more info from an old post:

http://motorbikearchives.com/Bike-Te...50EN-1979.html

The GS750B came with a # 100 main jet, 0-6 needle, 5F21-3 jet needle, and # 15 pilot jet. The GS750C (1978) and GS750N (1979) carburetors were changed to a #102.5 main jet, 0-4 needle, 5DL36-2 jet needle and #15 pilot jet.

What that all means is that the GS750N is leaner at the small throttle openings usually encountered in EPA emissions test modes. The dual-taper 5DL36-2 jet needle is initially leaner, secondarily richer to smooth the transition from idle to off idle, (or from small, steady-state carb openings at low speeds to gentle acceleration, as encountered in traffic). The float level was also lowered between the GS750B and GS750N, from 26mm to 24mm.
 
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My 78 has the springs and two plastic washers per needle. As stated above, it has the 5DL36 needles, 102.5 mains and #15 pilots.
 
'78 and '79 VM26 use the thicker nylon ring above the e-clip and the thinner spacer below the e-clip. The spring is also used.
I don't know about the '77 carbs.
 
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