Many little carb facts
Posted: Wed Oct 17, 2018 7:12 pm
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.
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.
