Drove around Vegas with it pinched off so I would not look like a dufus with a back firing 340. Never even dreamed about burning up valves.
I dunno. never had any indication that the brake booster was leaking. power brakes were still working great.
I'd guess that the difference between burned exhaust valves and not, is that you identified the leak as the booster immediately and plugged the hose so it wasn't continuing to run lean, where as it took me longer to find the source of the leak. I spent a lot of time messing around with the carb, gaskets, etc. looking for what the source of the popping was before I found it was the leak.
Heck, I even thought that maybe my spark was getting weak since it was not idling funny, still driving fine, and would just backfire occasionally under load. spent some time swapping parts there too, thinking it was from weak spark, before I went on to look for vacuum leaks.
I had no idea how bad things were until it started to really drop off in power. funny thing is, that even running on 5 cylinders, it was still smooth and didn't show signs of missing. it was just much slower than usual. that's when I broke out the compression gauge and found 0 PSI on 3 cylinders.
