The Stovebolt Site Forums The Parking Lot Big Bolts Heat riser and the valves

If the condition of your valves worries you, run a compression check. A stuck closed heat riser will cause them to be hard to start when they are hot because it will boil gas out of the carb, but damaging the valves sounds a little way out to me. A more likely answer to your engine suddenly not idling is that you have crap in your fuel system or fuel bowl and it moved around. Sometimes you can rev an engine up and put your hand over the carb for a little bit. The extreme vacuum quite often sucks the trash on through. Maybe you should look for a mechanic who has experience in 50-60 year old engines.