The Haynes manual calls for 3-1/2 turns out... exactly where my modified B12 likes it. The factory Suzuki manula just says, "PRE SET".
Big question: How much work has been done on this bike, previously? Any "performance" mods?
One thing I learned the hard way:
MY B12 HATES A DIRTY AIR FILTER. Even SLIGHTLY dirty... I was riding across Colorado and the bike ran worse and worse...I CHECKED the air filter and thought all was fine...looked decent,,, wasn't until I finally took a chance and put a fresh one in there that it suddenly ran tip-top.
Also-
MY BIKE WILL NOT TOLERATE AN AFTERMARKET AIR FILTER. This could just be my jetting set-up...I don't know, but no way will it take one of those crappy EBay "Emgo" filters. Suzuki ONLY for mine, whether I like it or not. It runs like Ca Ca without an OEM.
If that bike has been sitting for ANY length of time, I will GUARANTEE that your bank of carbs needs to come off for a complete douching. Most likely are the pilot jets are clogged, which are very small and seem to jam-up pretty easily when any sort of dirt is present. That would DEFINETLY cause your symptoms.
Check for ANY signs of rust inside your tank using a flashlight, (avoid using a match). If you see ANY signs of sediment you absolutely will have to deal with that... as it will never go away, and you will be pulling those carbs out for cleaning continually. If it's rusty in bottom, it's usually along the bottom seam...sometimes hard to see. If necessary drain the fuel into a clean bucket and look for flakes of rust or signs of grit. If a tank is rusty, it CAN be cleaned nicely by using Muriatic acid (from a pool store). This should be done carefully,,, as it can get messy... but it WILL clean a slightly rusty tank.
If you take the carbs apart (& I highly recommend it, as this is where 80% of all performance problems start: DIRT), take the flat black vacuum caps off the top of the carbs carefully, on a table... and as you do look to see if the little tiny black O-rings are still in their little cut-outs on the top of the carb bodies. Those are easy to loose, and if someone disassembled your carbs before, it's very possible one (or more) of those popped-out. This would cause a vacuum leak... maybe cause your symptoms.
When you put the big vacuum caps back on, take a tiny...TINY amount of RTV sealer and smear the O-rings JUST SLIGHTLY... don't clog the hole...and they should stay in place next time. Reassemble carefully, don't knock them loose when screwing the tops back on.
But if you make sure the tank is pristine, and the carbs well sprayed-out with carb cleaner, including all the tiny orifices...hosed-out with an air gun.. Fresh OEM air filter... Chances are excellent that your Bandito will run like a Sexually Abused Orangutang.
Check the connections to your coils, and make sure the plug-caps are screwed-on the wires completely.. nothing loose or corroded. I've rarely seen coils go bad on these Suzuki models...unless someone futzed with them. LOOSE CAP... yes, perhaps.