You're gonna have to pull the carbs and clean things well, also while your there you should set the float heights and make sure your floats are not stuck shut which it sounds like. Also check the float seats to make sure that they are screwed all the way in, my 80 had #1 about halfway out and had holed the #1 piston and this condition still existed after the PO had a local "performance" shop go through and repair, and B+B the motor.
Once you get the carbs out clean them thoroughly and pay particular attention to the idle jet, you should be able to squirt cleaner in the jet and have it come out of the idle mix screw hole with the screws out, this is only a .0135 in. hole so it is not easy and eye protection is recommended, don't ask how I know this. Be careful not to lose the spring and very small washers in the bottom of the idle screw holes when you take the screws out as well. Also look at the anti-backfire valve and replace it if it's not real pliable or has any holes,rips, etc. I would also suggest that if there is much varnish in the carbs which is probable you might want to save yourself some grief and just get some new float needles up front because they will probably have a problem as well.
Once this is done balance them well and enjoy. Hope this helps,
Steve P. #5220