GS550 with Mikuni Dual Throat Carb, No Info

[Witehorse Motors]

An acquaintance brought me a chopped out custom GS550, needs wiring and revival. It is sporting a set of the Mikuni "dual throat" carbs with 2 carbs running 4 cylinders. I have seen posts online from 15 years ago that attempt to gather specs and info, but none of them go very far. I am trying to learn all I can about these carbs in hopes of overcoming the obvious flaws in this chopper set up such as chopped exhaust and lack of air box.
I would love to know the history of these carbs, what to look out for in tuning them, why they seem to have different main jets on 1 and 4 than they do on 2 and 3?? etc...
They look like they can be saved with a good amount of effort. I have found parts diagrams and my with my first look inside the carbs they seem to need only bowl gaskets, but my goal is to find as much out as I can before attempting to rewire and tune the bike. These units seem like another short lived 80's part quickly orphaned by progress.
ANY help would be great.
Thanks for your time.

[Witehorse Motors]

The parts diagram showed it was for a 1983 GS550L BTW.. I have seen references to the bike being a GSX but cant confirm. The internet is not much help for this one.

[Nessism]

You can download the factory manual for the bike here...https://gsarchive.bwringer.com/

Different jets is because some cylinders ran hotter than others.

[zed1015]

It is sporting a set of the Mikuni "dual throat" carbs with 2 carbs running 4 cylinders. I have seen posts online from 15 years ago that attempt to gather specs and info, but none of them go very far. I am trying to learn all I can about these carbs in hopes of overcoming the obvious flaws in this chopper set up such as chopped exhaust and lack of air box.
I would love to know the history of these carbs, what to look out for in tuning them, why they seem to have different main jets on 1 and 4 than they do on 2 and 3?? etc...

Sounds like a home spun conversion possibly using a pair of Z1300 or Mikuni Solex N40PHH ( Datsun etc ) carbs
Pics would help..
The different jetting is usually to correct the A/F ratio caused by differing air flow rates through unbalanced airbox intake or manifold tracts.

[Nessism]

Sounds like a home spun conversion possibly using a pair of Z1300 or Mikuni Solex N40PHH ( Datsun etc ) carbs
Pics would help..
The different jetting is usually to correct the A/F ratio caused by differing air flow rates through unbalanced airbox intake or manifold tracts.

No. The second gen 550, with 16V, came with two, dual throat Mikuni BS30 carbs.


Screenshot 2025-06-12 164914 by nessism, on Flickr