This is on my '48 GMC, 228 engine. The heat riser is stuck and I've been trying to get it freed up with no luck so far. I have the exhaust system off for some new pipe and took the opportunity to look at the flap position inside the manifold. Am I correct in thinking that the flap should be completely closed? The picture shows it doesn't fit flush, with an opening about 3/8" wide. One of the quirks of this truck is that after the engine is completely warmed up it will only idle for a few minutes then slowly die out. I'd like to get the flap free and restore its proper function and it would be great if it solves my weak idle problem at the same time. What do you think?
