If an exhaust valve is not opening at all, the engine will regularly pop in the intake/carb and more violently as the engine throttle is opened.
If the exhaust valve is not opening enough, as in a badly worn cam lobe, I've had v8's idle perfectly and run good at part throttle then when throttle is opened would regularly pop,pop,pop,through the carb.
Observe the exhaust valve action if the valve cover is removed.
Also you may isolate the offending cylinder by removing one plug wire at a time.
Have seen an engine pop back from a leaking head gasket that burned away between 2 adjacent cylinders and didn't leak water.It sure didn't idle well though.
