I've searched on here, and found many articles about timing, vacuum, etc about similar issues, including a very specific one about popping sounds from the engine on a 235 (same as mine), but none are quite exactly what I am hearing and seeing (I don't think). When the engine is cold, or under load at all, it runs smoothly. Once it is warmed up, or even close to normal op temp, I am getting a popping sound that I can hear both at the carb/manifold area and in the tailpipe. Almost like a backfire, but not nearly as loud as I have ever heard in any other vehicles. Is it just a baby backfire? It's every couple of seconds irregularly. It only happens at idle, and usually only after I have slowed down. If I put the clutch in at speed for example, it will not do it until I have almost come to a stop, which seems odd to me. When it happens, I have sometimes seen a little smoke around the intake. The heat riser valve jumps as well, but since I can't make the noise happen by fiddling with it, I assume that is a symptom and not the cause. Any suggestions on this? Or should I just go through the normal timing and vacuum checks and adjustments and hope it goes away? This is a '59 3/4 ton with a 235 BTW.
