Carb/idle question

[nuttyprof1]

Just checking on one thing. My 2003 1200 BanditS runs poorly at idle, but great otherwise, even when cold. I did reset the a/f mixture screws, which helped a bit, but it is not consistent, meaning that it can run fine and then the next day not so good (at idle only). Once it is nice and warm (after 15 miles or so of freeway at 80 mph), then it idles OK, though not quite purring as I would like. Bike is stock: it sat for a while, but I bought it last month with 1000 miles and put on about 1200 miles of my own since. Now for the question: when I first reset the a/f screws, I pulled them out and noticed that the screw tips were dirty, as in black, etc. Cleaned them up, put them back in, and about 400 miles later, I pulled one out yesterday and it was dirty again, with what I would consider abnormal dirt for this kind of stuff. When I have worked on other bikes' carbs, I seem to remember that those tips were pretty much clean as can be when I pulled them. I also pulled one carb bowl, but it looked very clean inside. I am beginning to suspect some dirt in the fuel tank, not big chunks, but more like dust (the bike was stored in a garage off a dirt road and, although in great shape otherwise, was quite dusty in general). Any ideas? Do you think I am on the right track? Anything else I am missing or should do?
Thanks

[Red01]

Captain Obvious says, "How's the air filter?"

Since you can access your mixture screws, there's a good chance the carbs have been off before. Are there any leaks where the carbs mate to the manifold or where the airbox mounts to the carbs? A manifold leak will make you lean,and if it's a tiny leak, could cause poor idle but not be bad enough to have a serious effect on performance at higher rpm. A poor airbox connection won't do that, but could allow unfiltered air into the carbs and let things get dirty that are normally clean.

[nuttyprof1]

The air filter is fine and I cleaned it when I first adjusted the screws. I thought the manifold connections were good, but I will test them by the spraying method, just to be sure.
That's a good suggestion.
Giulio

[99er]

If the bowls were clean, I expect the tank is same. The dirt would settle to the bottom of the bowls while sitting so you probably should look elsewhere. I've never seen this on a motorcycle but it would prompt me to remove the carbs for investigation. Is your airbox tight to the carbs? Since they have been removed before, it is possible that the boots are not properly mounted and filth is geting by the filter. Is the filter properly seated, etc. Are all needles the same, dirt wise? Strange problem.
Marc/Atlanta