I have a 1980 SR500 that runs great, starts easily, idles great (sometimes). Other times it will die when coming to an idle at a stop light, etc. The bike always starts back up, but sometimes just won't idle. Can't figure it out. I have cleaned and inspected the carb and air filter, put in a new plug. Any ideas?? Thanks

I'd say the mixture was too rich at idle, thats what normally causes this.

A lot of carb problems on this bike are put down to the diaphragms, however this is USUALLY combined with hot starting problems as well. As your bike starts OK hot, I'd look at the pilot mixture settings and then pilot jets in the carb.