[rufus]

First of all, you can build a very effective vacuum guage with some aquarium tubing, t-fittings, and colored water, for just a few bucks. A Google search should turn up plans and directions on use.

Second, you can get some good information on your air fuel mixture from your spark plugs. Google "plug chop" for more info on that one.

Shimming the needle normally involves using some very small washers to adjust the needle's position relative to the jet orifice for any given position of the vacuum diaphram. Or maybe it changes the position of the slide... I can't remember right now.

Finally, make sure you clean every little passageway in the carb bodies with some good carb cleaner and a very fine brass or copper wire, and refresh all of the rubber o-rings throughout the carb. A tiny leak or blockage somewhere can have dramatic effects on the performance of the carb. Also check the condition of the float needles to make sure the "cone" is not worn or pitted.

When you pulled the float bowls was there any rust or gunk in the bowls?

Check out the message board at gstwins.com. It is focused on the GS500, but there is a ton of information there that should be useful to you as well.

Hope this helps.