OK, I'm about a year into working on my '91 Suzuki GSF400 project and I am still struggling with getting a good set of four carbs sorted. I currently have a few issues, mainly a non-functional choke (actually cold-start enrichment, but choke is easy to understand) as well as a damaged pilot air jet, and now a slightly bent throttle plate from my hamfists berkeleying with it in an effort to fix it.
I now have three sets of used carbs. 
I recently bought another set of used carbs and tore all my sets apart (including the one I rebuilt to the best of my ability a little while back) with the idea of combining the best of all sets into one super set. The big setback here is that the spare set I have has 33mm throttle plates, and bodies bored to 33mm. It also came with 102.5 main jets. The original set I am working with has 32mm throttle plates in a body externally identical to the 33mm set (bored to 32mm internally,) and worked pretty well at large throttle openings with 97.5 main jets...so mixing and matching ain't going to work!
The enrichment issue is due to E36 M3ty aftermarket "starter caps" AKA the rubber bit that goes around the shaft of the plunger for the cold start enrichment. It hangs up and won't open well, and often won't close at all. I've fiddled and berkeleyed with it, I've lubed it, I"ve mixed and matched plungers and rubbers hoping for the best fit, and even tried fitting double return springs to no avail. That's issue number one.
Issue number two is a slightly-rough-running in the lower mid-range at steady throttle to very, very light acceleration (roughly 5,000rpm.) Chasing this issue is what got me tearing back into these things in an effort to play with jetting, float height, etc. At this point I don't really give to flips about the funky rough running at cruise anymore, I just want to know I can source the parts to put a good set of carbs together.
The remaining issues are a result of suspect parts uncovered in my latest looksee and rebuild attempt.
Here's the problem....nobody seems to have a good selection of parts. Suzuki has discontinued many of the parts that I would need. Used carbs only show up on eBay every blue moon, and usually for hundreds of dollars in need of rebuild. Sudco has a 500-some-page catalog, and they carry....uh.....float bowl seals, main jets, and pilot jets and that's it. carburettorshop.com has....hmmm...float bowl seals and a few universal tools. Niche Cycle Supply is one of the few places to carry pilot air jets, but not in the right sizes. LiteTek in SE Asia has a good selection of seals, but the ones for the enrichment plungers don't seem to fit. 
motocarb.com...nope. mikunipower.com....nope. I bought a jet kit from Factory Pro, which seems to be of really nice quality, but it contains needles, main jets, pilot jets, and a few hardware bits. It would seem there are tons of places carrying float bowl seals, needles, main jets, and pilot jets, but nothing else.
Where does one buy stuff like pilot air jets, throttle plates, needle jets, replacement float bowls, and the like?
I know that one can't expect the aftermarket to support older models forever, but one would think that the carbs for pretty much every Suzuki GS, GSF, GSX, and GSXR models, as well as the DR dual sports, and BMW's F-series bikes, and all the KTM LC4 models, and several Triumph models, and Pegaso, and Polaris ATVs...I guess I thought the aftermarket for basic carb parts might exist. 
Is there some hidden source for parts I don't know about? How do you go about trying to tune a set of carbs when you can't even buy jets to tune them, or replacement parts for the messed up bits you find when tearing sets of eBay carbs apart?
