Hi there.

I think I need to adjust my carbs after getting a new muffler on. But from what I can tell, the screws have plugs or something in them? how can I get to the adjusters? Your advice is appreciated

A

CAREFULLY drill a pilot hole in the little brass plug (not too deep).  Then take a drywall screw or sheet metal screw, and screw it in...enough to get a grip.  Then take a pair of pliers and give it a yank.  Should come out.

A conservative starting point is 3 turns out from the seated position.

Here are some useful carb pages.  Next time use the search function first.  To access the mixture screws drill a hole in the cap and use a hook or screw to pull the cap out.

http://gstwins.com/gsboard/index.php?topic=56601.0
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html
http://www.gstwin.com/carb_work.htm
http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting
http://www.ronayers.com/Fiche/TypeID/26/Type/Motorcycle/MakeID/2/Make/Suzuki/YearID/45/Year/2004/ModelID/6807/Model/GS500F/GroupID/290246/Group/CARBURETOR_MODEL_K4