1980 Suzuki GS450S - Identifying the idle mixture screw

[seinwave]

It's surprisingly difficult to find a clearly-labelled diagram of the Mikuni BS34SS carbs and what adjusts what -- I haven't been able to find one. I suspect the fact that they weren't intended to be adjusted is partially to blame.

Is the screw I highlighted with the red box in the attached image the idle mixture screw? Based on written descriptions, I'm pretty sure it is, but - again - haven't been able to find an actual image to confirm. I also thought that the mixture screws were blocked by little anti-tamper caps, but none of these seem to be present on my carbs.

If you could confirm that 2-3 turns out is a good place to start playing with if I'm trying to chase down a hanging idle I suspect is caused by a lean condition, I would also appreciate it.

 

[tom203]

Yes, that’s the idle mixture screw. Later carb versions had this area moved to top of carb throat , since 4 ganged carbs needed a different approach! Someone probably removed the anti tamper caps for you as a courtesy. Hanging idle is often caused by air leak at carb, maybe leaky boots ,but a bad petcock or vacuum line could be an issue. Safest bet is to carefully removed the mixture screw and make sure it ain’t damaged…should be pointy.
have you followed the advice on here and properly cleaned carbs?

 

[seinwave]

Thanks for the confirmation. The issue you mention -- busted screws -- is actually why I wanted to play around with the idle screw before popping open the carbs - wanted to gauge likelihood of busted brass to see if I needed to hunt down OEM brass in addition to rubbers for the clean. Hanging idle was mostly resolved by reseating the air filter and completely resolved during valve adjustment when I noticed a breather hose had worked its way loose, though. Carb clean up next.