Ok I lied about fixing the stumbling problem the last post. Actually everything would be fine, until you have the A/C turned on, and the idle speed would drop below 800RPMs, causing the engine to sputter and die out. I 1st tried adjusting the carb with the A/C on, not happenning, the fuel mixture screws were responding sluggish, bypass screw wouldn't bring the idle speed up even with it dangerously close to totally out. Pumping the accelerator would also cause the engine to cough and die, this was due to too big an accelerator pump output, so a quick adjustment fixed that.
PMed Keifernet over at TheSamba (http://www.thesamba.com/vw/forum/profile.php?mode=viewprofile&u=27&sid=d068d891b9191df5c9c889952e13e2c4), he has experience with Gilmore A/C units.
Although not recommended for normal carb tuning, he suggested I screw the fast idle screw in a turn to bring up the idle. I did that, and could now bring up the idle speed to the proper range (800-900RPMs).
So now what I do would be, adjust carb with A/C off as per normal. Turn on A/C, re-adjust carb with bypass and fast idle screw till I get the idle speed right, try to lean it out a little on the mixture screw.
I think the lowered RPMs due to the A/C compressor really screws with normal idle fuel metering. If I crack the throttle open using the fast idle screw to bring up RPMs, the mixture becomes seriously rich (smelling the tailpipe and getting stung by the exhaust will tell you that). I have yet to fix this problem totally, the spark plugs still read rich (black and sooty), if I don't use the A/C, and tune the carb as per normal it'd be fine (no sooty spark plugs).
Maybe I'll try tweaking the idle advance next.
If anyone has any tips on how to fix this problem, do let me know.