GS550 with Mikuni Dual Throat Carb, No Info

[Griffin]

I'm not surprised. The 16 valve '83-'86 GS550E/ES/L models were not made in great numbers, and had a tendency to wipe crankshafts if used for racing for extended periods of time. They had many parts unique to that bike only.

I had an '83 I used for racing in '86 and '87. They were very competitive with the GPZ550 and XJ550 Seca & FJ600. But then the the 600 Ninja came out in late '85, and the air cooled middleweights were swept off the track..

Your customer is best served by parting the bike out and finding a more common bike from the period that hasn't been put under the sawzall. The owners of the few left in good shape could use the parts.

[Witehorse Motors]

Well I was away for work but I'm back now looking at the carbs and getting ready for a deep cleaning, there were two hoses just venting to the atmosphere on each of these fittings which seems like on a lot of old Japanese bikes they should be connected to each other

[Witehorse Motors]

Also the parts diagram does not specify what this fitting is I would assume it is event for the bowls, it looks like it used to have a hose coming off of it that rotted Off

[Witehorse Motors]

Well it may not be easy or fun to work on but this is someone's chopper that they put a lot of effort into so I've got to try my best, up to a point of course

[Witehorse Motors]

Hmm.. I think it may be a vacuum petcock fitting actually. This tank is not using one. I will cap it later.

[Witehorse Motors]

[Witehorse Motors]

Well the crossover tube between carbs is easy to see and the image in manual describes that fitting as breather tubes, nothing in the emissions chapter on the actual breather type or location.

[Witehorse Motors]

Great diagrams in the FSM, nice to have the link

The first real deal-breaker may have popped up though, 1 of 4 fuel air mixture screws is stuck in carb.
All 4 look like they have been mistreated but this one has less of the slot left and is not bunging so far.

Couple cycles of PB Blaster, then some propane heat... Couple gentle whacks with impact reduced down to 1/4" bit .. no love so far

[Witehorse Motors]

Continuing nightmare. I drilled out that air screw as best I could and managed to get the threaded portion completely out, the needle part of it moved downward into the car body but what I see is part of the shaft and the washer or hopelessly seized in the hole. I'm just looking at them now and cursing.

If only that needle would come out I would have had pretty much everything else needed to revive the carbs. Even if I had to oversize the hole and press a bushing in order to drill it out and tap it for a new threads. The thread pitch is 5 mm but I'm sure I could find the proper tap online.


What an incredibly frustrating ordeal

[Witehorse Motors]

I can see that the heads are not set up to take a four carb intake, so that is out of the question.

I have to assume that's all began with someone using the wrong size washer under that air fuel screw.

[dgates1]

I think your issue started with crud in the threads. That's why I had such an issue with my pilot mixture screws on my GS850G. They had never been taken out and there was a white buildup above the screw in the threads. Thought I had cleaned it up enough to get it out, but was wrong.

Different screw, so may be different sizes, but I did the same by drilling out the top. I was able to pull the spring out and then get some long nosed tweezers in there to remove the post. If you have pressed it into the carb body too hard during your drilling, you may have a hard time getting it to release. Try some focused heat on the bottom of the area (hole where this jet comes out). Maybe a dental pick from the bottom. I have heard of people using an acid that only attacks the brass to get these to fall out.

Link to my experience if it helps -

https://www.thegsresources.com/_forum/forum/technical-forums/carb-fuel-exhaust/1747809-fuel-mixture-screw-stuck

[DR Payne]

I just went through and cleaned my BSW30SS carbs on my '83 GS550E, and I can confirm:

1. There is not much info out there on these!
2. The outer jets are bigger than the inner jets, 102.5 and 95 stock, respectively (for the E, other models may vary).
3. That fitting is indeed for the petcock vacuum line. The breather fittings are bigger, and there's one on each carb, facing inboard. There's only one petcock fitting.
4. I had no springs on my slides either, other than the tiny springs inside the needle holders. Vacuum pulls the slides up, and I think magic pulls them back down.

Best of luck getting them in working order again! I got nothing for you on drilling out screws. I may have the lowest success rate in the world on that, especially in sensitive areas like that.

[Witehorse Motors]

Well the top 2/3 of the air mix screw is drilled out, but the remains and what looks like a washer are STUCK AF still, my neighbor tried to help but the tapered needle seems to have moved slightly downward into the carb body. I cant make any progress. And the 0.5mm pitch fine threading is damaged in the hole. Depressing.
If I could just get the remnants out I would try and find a machine shop and see if its possible to drill the top of the hole larger and press a bushing in there then thread it to the new air screw.
So bummed.
I have found the parts needed to get them working again.

I have yet to remove the intake boots from the head, but I assume the head is not machined to accept a traditional bank of 4 carbs. If I found a set.
I surely wish there was one of these carb bodies out there for sale.

[dgates1]

Here's some videos I found on alternative methods...

As I mentioned before using nitric acid. I'm not sure I would try it myself.

https://www.youtube.com/watch?v=XjdBvtOgqCU

https://www.youtube.com/watch?v=6DMYmAA8Bxs

And an elaborate way to use heat and air pressure. If you can rig this up, I'd say it's likely to work.

https://www.youtube.com/watch?v=PbDEuADGdYc

[Nessism]

Here's some videos I found on alternative methods...

As I mentioned before using nitric acid. I'm not sure I would try it myself.

https://www.youtube.com/watch?v=XjdBvtOgqCU

https://www.youtube.com/watch?v=6DMYmAA8Bxs

And an elaborate way to use heat and air pressure. If you can rig this up, I'd say it's likely to work.

https://www.youtube.com/watch?v=PbDEuADGdYc

Those videos are horrible.