Not the same carburetor question- I think

[Guest]

Hello to all, and thank you so much for all your help. This is the first time I haven't been able to search/find an answer. I bought my 1981 GS850G about 18 months ago, and began the teardown and near-restoration about a year ago. (This is my second GS. The first was a 1977 GS750.) At that time the bike ran pretty well. I made all kinds of mistakes and continue to do so. First, I put the entire carb rack in the dishwasher to degrease it. Worked great, but oxidized the hell out of the carbs. So I soda-blasted the outsides, rebuilt-ish them, painted them and spent the next 6 months working on everything else. I finally got the bike together, re-wired, and filled with gas, and I was having a fuel/air delivery problem so I decided to rebuild them for real this time. Berryman's, rebuild kits from Z1, the whole deal. In my zeal to tear them down, I stripped the air screw (the one under the cap) in the #1 carb. It was turning out, got real hard to turn, then stopped. I used pb blaster, gentle heat from a butane torch, and nothing. By this time the slot was stripped, so I decided to drill it out. I drilled a hole in it, inserted the extractor, and it snapped. So, I bought a replacement from ebay from a 1980 GS850. The thing looked identical to the original three, and all the bits and pieces fit nicely. Now I have a cold cylinder in #1. Upon closer inspection, the new carb body seems to be missing an additional passage in the corner (opposite the brass tube that sticks into the bowl) that gets sealed up by the float bowl and gasket, and the brass tube has a reducer in its opening. I have new dyna coils, new spark plugs, new wires. Cylinder 4 is hot. Could these anatomic differences really keep the fuel from being delivered? I should say that the exhaust does get warmish with full choke. Removing the spark plug wire at idle does not change the revs at all. What are my options?

[TheCafeKid]

I know it sounds like a PITA but can you take a pic of the inside of that odd carb? Im not quite picturing what youre saying but it sounds like perhaps the pickup tube has been broken off? If so that would definitely cause a problem.
It's also possible you've picked up a carb from a different model GS (like a twin that may have used BS32s as well but they had some differences) or a carb from an entirely different brand. Mikuni, as you may already know, made carbs for many different manufacturers from Suzuki to Kawasaki on and off as well as some Yamaha models. The old Hondas as far as I know, and I'm no Honda expert, almost exclusively used Keihin carbs. Kawasaki kept switching back and forth between the two companies, and I think Yamaha did the same thing.

Even though they may be BS32s, the internal design for a different manufacturer were often somewhat different, besides the jet sizes.
Also, the 80 and on GS750s used the same BS32SS carbs as your 850, but the 16 valve engine bikes had very different jets and likely the needles as well (I've never checked the needles) The 16v bikes often had smaller jets compared to the 8v bikes...just things to watch out for and keep in mind.

Lastly, the carbs were often different internally even off of the same bike depending on where they were located on the fuel rail. The number 2 carb had different passages closed or opened because it was the carb that created the vacuum "signal" for the petcock to operate when the engine spun over. Swapping this carb to another position on the rack may cause problems. The number 3 carb was often the "master" carb to which the rest of the carbs on the rack would be synced because it didnt have a sync adjuster. Again, swapping this carb on the rack may cause issues.

This is one of the reasons is so important to number your carbs and keep all the parts separate when preparing them for cleaning and reassembly.

If it turns out that the carb you have isn't going to work, I *may* have one for you that will. It will depend on which one it is. I have lots of BS carb bodies, but usually one of the four in the rack was too far gone or severely damaged to keep. I may even be able to build you a complete rack for a reasonable price, ready to go if you'd like. (they'd still need to be dynamically [or vacuum] synced to your bike as I cannot do that without the bike here, but I could get the bench sync really close and good enough for you to ride, it just might be a little "buzzier" than it would be after a vacuum sync)

See if you can get us a pic of that carb, I know it's a pain to have to pull them again, but it will make it much easier for us to point you in the right directionif we can see what's going on. And lemme know if I can be of any help.

[rogerramjet]

As you can see, there is a small hole in the #2 carb that is not in the #1 near the upper left screw thread of the carb body next to the float post. I have confirmed by looking at the old #1 that the hole should exist. What is weird, is that while the gasket has a hole for it, the float bowl does not. That appears to be the only difference between the two, and for what it's worth, the rebuild kit is for the '80-'83, so I'm still a bit perplexed why it wouldn't work. I guess the easiest thing to do would be to replace it with an IDENTICAL one and end the hair pulling.

Thanks again for any and all help.

[Steve]

Even when you find a 'proper' carb, there might still be some hair pulling.

After the dishwasher incident you soda-blasted the outsides of the carbs.

Did you also soda-blast all the little passages inside the carbs that probably look just as bad as the outsides did?

Your engine doesn't really care how oxidized or grungy the outsides of the carbs are, but it DOES care about getting proper quantities of fuel and air, in the correct proportions. ANYTHING that disrupts the flow in any of those passages will make your engine rather unhappy.

When your engine is unhappy, YOU will be unhappy.

.

[rogerramjet]

No doubt about the "all will be well" sentiment. Part of me can't wait to find out what else needs to be tackled.

I intentionally didn't soda blast the insides, because I didn't want to risk reaming out passages or disrupting threads, openings etc. I used the carb dip to clean the insides. Plus, I washed them closed as a unit, so there wasn't much "extra" oxidation inside.

The new carb body wasn't involved in the oxidized-soda-blasting rigamarole, it just won't ignite the cylinder like the others.

[tom203]

As you can see, there is a small hole in the #2 carb that is not in the #1 near the upper left screw thread of the carb body next to the float post. I have confirmed by looking at the old #1 that the hole should exist. What is weird, is that while the gasket has a hole for it, the float bowl does not.
Thanks again for any and all help.

Yeah, something is odd here. I just looked at my spare carbs, the punched gasket hole goes over that little hole and then overhangs the float bowl edge meaning that the little hole is "exposed" to atmosphere -it must be some sort of vent for the carb throat in air screw area- it doesn't connect to float bowl. The carbs on my bike also show the overhanging gasket.