Many little carb facts

[mikenixon]

The choke linkage on a 1975 GL1000 carburetor has a screw on the actuating arm that enables synchronizing the choke action between the left and right carb banks On later year carbs it's absent. If you want to sync the chokes you do so by, consistent with traditional automotive carburetor practice, bending the linkage rod. It's rarely needed however.

The earliest 1975 GL1000 carbs also have a jet screwed into a blind hole. The hole doesn't go anywhere. On later 75s and all subsequent years the blind hole is still there but there is no jet screwed into it, or even threads. The hole itself is an anachronism, that is, a leftover from before the carb was repurposed from its original role on a Honda car engine.

GL1000 float pivot pins are pretty unique among Keihin carburetors. They are a smaller diameter than most of the pins on Keihins, they have a taper on one end, and, the carburetor's posts that accept them are made like no other Keihin's posts. Specifically, the two posts on the GL1000 carburetor have differently sized holes, similar to what you'll find on older Mikuni carbs. Therefore, the pin must always be inserted in a certain direction.

It's pretty well known by now that on all the four-cylinder Wings, the float bowls are arranged so that the drain screws are close together, that is, biased toward the center of the carburetor set. This allows easy access to the screws by pointing a screwdriver between the intake manifolds.

The GL1000 carbs have a perfectly flat plastic ring under each slide. The GL1100 carbs' plastic ring however is stepped and must be installed with the step or ridge upward. If it is put in upside-down it will permanently deform when the vacuum top is screwed down.

Speaking of the vacuum chamber on the GL1000 and GL1100 carburetors, as odd as it seems, the vacuum top on these carbs seals to its carb metal to metal. Two things are significant about this. First, the plastic slide ring is not, as many suppose, a gasket or any kind of seal. The seal is purely aluminum top to aluminum carb body, both of which are precisely machined for this purpose. Second, this means any imperfections: dirt, metal burrs, dings--even left over polishing compound--on the vacuum top's machined mounting surface can degrade that vacuum seal, and just as importantly, tilt the top enough to cause binding between top and slide. And if a spec of dirt can have this effect, what do you suppose chrome, paint or powder coating will do? I won't guarantee rebuilds on carbs that have chromed or painted vacuum tops.

The aluminum epa stop flags on GL1100 carbs are easily removed in-situ using a pro level soldering gun. I have a video on my website that shows how to do it. I am saddened each time I see a carb set that has never had the flags removed. Just think: for some 30 years this bike never received a proper maintence service.

The pilot mixture screws in GL1100 carbs often are frozen in their threaded cavities due to fuel resin that is nearly as hard as epoxy. To avoid snapping the head off a screw, carefully heat the outside of the cavity and the resin will dissolve and the screw will turn.

In each case where someone believed the felt throttle shaft seals to be the cause of an unwanted performance glitch, I have found that there was another, completely different issue. Whether bowl venting problems, incomplete cleaning, inadvisable use of aftermarket parts, ignition timing issues, or simply inexpert carburetor adjustment, these shortcomings are very common. The fact is, the felt seals on carburetor throttle and choke shafts are not perfect seals and are not designed to be. They are dust seals only, and the carbs engineered to work properly with this small air leak. I sell these felt seals, in all four sizes, because folks want them. But they don't solve performance issues.

When I install four-cylinder Gold Wing carburetors, I leave the manifold clamps loose, and leave the chrome decorative plates off. It's while the manifolds are still unbolted, allowing the sliding of the carbs around, that the aircut valve (GL1000) and the three cables are easily installed. Then I bolt the manifolds to the cylinder heads (don't forget new o-rings), and afterward tighten the manifold clamps. Lastly, I install the decorative chrome plates.

[twooldwings]

this came up while i was searching for something else. there are a couple of paragraphs in here that would have saved me a bucket full of tears on past projects. i found the info about the vacuum cap to carb body seal particularly interesting. thank you.

[mikenixon]

You are very welcome. Thanks for reaching out. Merry Christmas!

[nakedinterstate81]

I have the blind jet you mentioned. Drove me nuts because I couldn't find any info about it and the cylinder on that carb ran cold on my first rebuild attempt.
Also the springs in the connecting rods are driving me nuts. It returns to a high idle but not fully. I have to tug on the rod to get it down to 1000 rpm. Are there any known solutions for that?

I am running 1100 carbs now on the 1000. It runs fine, definitely no more off idle stumble but I can feel that it's not the perfect match. Even with the one cylinder not fully working the original carb pulled harder.

I would like to make a better linkage and find out why this one cylinder is not running hot like the others.
Float bowl heights are double checked.

[gltriker]

Also the springs in the connecting rods are driving me nuts. It returns to a high idle but not fully. I have to tug on the rod to get it down to 1000 rpm. Are there any known solutions for that?

maybe this article has the information you seek.
https://www.wingovations.com/earlygl1000throttlearmfix

[mikenixon]

But my feeling in your case is the hanging idle symptom needs to be got after before modifications are brought to bear.

[nakedinterstate81]

maybe this article has the information you seek.
https://www.wingovations.com/earlygl1000throttlearmfix
[/quote]

Thanks triker, this one came up first on a google search I did earlier.
I didn't have time to take it apart and understand his post yet.

How come ngwclub never comes up in any google searches? Just GWdocs and other forums.

As for the off idle flat spot there are some recommendations on Randakk's blog.
I am trying to figure out which one would be easier to execute.

[pidjones]

As for the off idle flat spot there are some recommendations on Randakk's blog.
I am trying to figure out which one would be easier to execute.

The question isn't which fix is easy but which one works on your bike. Note that most are year range specific.

[Sidecar Bob]

The GL1000 carbs have a perfectly flat plastic ring under each slide. The GL1100 carbs' plastic ring however is stepped and must be installed with the step or ridge upward. If it is put in upside-down it will permanently deform when the vacuum top is screwed down.

Speaking of the vacuum chamber on the GL1000 and GL1100 carburettors, as odd as it seems, the vacuum top on these carbs seals to its carb metal to metal. Two things are significant about this. First, the plastic slide ring is not, as many suppose, a gasket or any kind of seal. The seal is purely aluminum top to aluminum carb body, both of which are precisely machined for this purpose. Second, this means any imperfections: dirt, metal burrs, dings--even left over polishing compound--on the vacuum top's machined mounting surface can degrade that vacuum seal, and just as importantly, tilt the top enough to cause binding between top and slide. And if a spec of dirt can have this effect, what do you suppose chrome, paint or powder coating will do? I won't guarantee rebuilds on carbs that have chromed or painted vacuum tops.

I've long known that those rings aren't seals but what are they for?

I don't know if it is related to any of this information or if this is a good place to ask:
I'm running '79 carbs, currently on an '82 engine with '77 cams, Dyna S ignition and GL1500 coils but on a stock '79 engine when this started. It runs well and the idle is the normal 1000 RPM most of the time but occasionally the idle increases to about 1200 RPM or so. When the idle increases it still runs normally and everything else feels/sounds normal so this is more annoying than anything else.
When it started happening I spent a bunch of time synching and adjusting the carbs and checking everything I could but the problem always came back in a few days. One day I looked down at the carbs while at a stop with the idle high and decided to push the balance screw on the #4 carb down and the idle went back to normal for a few days. Since then I've done that many times and it can stay normal for anywhere from a few hours to a couple of weeks (it's hard to judge the last couple of years because I barely use the bikes enough to justify having them).
When I had the carbs out while changing the engine I went over the linkages carefully and couldn't find anything binding or loose and the cable (only 1 - I believe throttle return cables cause more problems than they could ever prevent) is not binding either.
Any suggestions?

[Whiskerfish]

I always thought those plastic rings were bumpers to lessen the shock of the slide bottoming out?

[CYBORG]

I always thought those plastic rings were bumpers to lessen the shock of the slide bottoming out?

So did I

[gltriker]

Me 3

[mikenixon]

Yeah, that's my take on them too. Cushions, not gaskets. Here's something to think about... Have you ever noticed that no two models of Keihin CVs that use those rings use the same thickness?

Bob, I have witnessed that also. In addition to simply linkage friction and random pneumatic fluxuations, neither of which are harmful of course or indicative of trouble, I would look at testing the throttle plates for proper centering on their shafts.

[Sidecar Bob]

I've never had the plates off of their shafts but I'll try to remember to look for that when I can get at it again in the spring.
I was wondering if wear where the shafts pivot could cause it?

I thought the rings might be cushions (like the plastic buttons in 1000 carb tops and the plastic pieces in the tops of the shafts of the slides in the 1100 and other Keihin carbs) but are they wide enough to catch the edges of the slides?

[nakedinterstate81]

As for the off idle flat spot there are some recommendations on Randakk's blog.
I am trying to figure out which one would be easier to execute.

The question isn't which fix is easy but which one works on your bike. Note that most are year range specific.

It's a 1975, 755A carb.