[Hi_Fi_Guy]

First don’t chase carb issues unless you are sure compression, valve adjustment, and ignition timing are all correct. Otherwise you will only be chasing your tail. If those things are correct then look to the carbs.

It should go without saying to test fuel pressure, float levels, and ensure all jets/vents are free of debris before making any changes.

Popping on deceleration is a common issue for these carbs since they were set-up to meet emissions requirements This popping can be tuned out with some work. Are the Zeniths utilizing the emissions equipment or not? The enrichment devices are designed to trigger when you lift off the accelerator. If installed will most likely need adjusting To ensure it is functioning properly. If not installed then all the ports need to be properly tapped and plugged with cap screws to eliminate any air leaks. The stock jetting tends to lean towards emissions compliance. They respond pretty well to re-jetting and can be tuned fairly well but do not possess the same eager throttle response of a Weber. The Zeniths are very sensitive to heat and ethanol in fuel. You may want to run stabil’s anti-ethanol additive if you live in an area that adds ethanol to the fuel. You may need to run higher octane in summer months. I like the Zeniths ok but still find Webers to be better from a tuning perspective. That said they can be made to run well without popping so don’t give up.