Idle and exhaust smell Q's

[SanRafaelFaz]

I have the electronic distributorless ignition, which has made a huge difference 99% of the time. But that remaining 1%, like today, the idle will be off, so low that I have to either keep my foot on the peddle slightly or use the throttle pull under the dash to keep it running at stop lights. This happenes from time to time, very randomly and for no apparent reason. Hot, cold, just at right temp. Sometimes I can just rev it to redline and it will "re-set", but not today. Plus,when I pulled into my garage, the exhaust smelled very weird, like a mild sulfur which I've seldom smelled before. Are these things related? Any clue why the idle will just decide to set itself lower at random times? I know next to nothing about carbs, but someone told me that there's a diaphragm in the carb which can get worn. Could this have anything to do with it? Otherwise, she runs strong and very smooth off idle right up to redline.

[So Cal Mark]

the sulfer smell is caused by a rich mixture reaching the catalytic converter

[SanRafaelFaz]

the sulfer smell is caused by a rich mixture reaching the catalytic converter

I kinda had a hunch, but I didn't want to "guess". Thanks.
So what would cause this to happen on an intermittent basis?

[So Cal Mark]

if your carb has an idle solenoid, it may be loose in the carb body or the choke may not be working well

[SanRafaelFaz]

if your carb has an idle solenoid, it may be loose in the carb body or the choke may not be working well

I think that's what he referred to as a "choke diaphragm". He's Italian and can't always express in English what he's trying to tell me. Just went for a ride, once again idle spot on, RMPs steady in all gears and no smells.