compression test question
It has a miss, once in a while you hear a slight pop at the tailpipe, could it be a burnt valve, or maybe I need to redo the valve lash adjustment?
A once-in-a-while pop in the pipe is not a bad valve.
It is more likely fresh air getting into the exhaust system somewhere, accompanied by an over-rich low-speed circuit,and/or a faulty ignition system on at least one cylinder.And possibly late timing. These three (or four) often conspire this way. The rich carb,and/or unfired charge,and/or late timing, push raw unburned fuel into the pipe,where it mixes with the fresh air. When the mixture is just right, still burning fuel from any late-firing cylinder, will ignite that ready-to-burn mixture. This scoots the gasses down the pipe, and you hear the pop as it exits.
This is not the only way a pop is created, just the most likely.
A burned valve will pop every single time the associated plug fires. That cylinder is sending compressed burning gasses into the pipe on every combustion cycle.
A sticking-in-the-guide exhaust valve will do the same, but only when it sticks.But stems don't usually unstick themselves. Once they're stuck, they burn the valve, and the cylinder goes down, and when one of six goes on vacation, you know it right away!
There are other less common reasons for occasional popping.