Thanks JB. The car came with the choke cable bent and disabled, and while reconnecting the choke is on my long list of to-dos, I haven’t gotten to it yet, and therefore I never use the choke. But, I seem to remember reading somewhere that some ZS carbs have an automatic choke with some sort of bi-metal temperature sensitive spring. Could it be that I have an automatic choke that sticks ON sometimes? That would explain the rough operation of half the cylinders.
With that in mind, I pulled the plugs for a look-see. If the forward carb choke was sticking ON I would expect to see rich fouling on plugs 1 and 2, but instead I found this (see pic below). You know those charts that show different plugs indicating too rich, too lean, too hot, too cold, etc? It looks like I’ve got one of each! Number 3 looks particularly bad. Not sure if this is related to my rough running issue, or if I just opened some new Pandora’s box.
Tom