My first experience with HEIs was when I bought a truck that had one. The truck didn't run especially well so I did a tune-up and that helped. I found the pushrods were different lengths and the rockers were badly worn, so I replaced those and rebuilt and tuned the carb, which helped but it still kinda "chugged" at idle and stumbled on acceleration. I gutted the cat, but that made no difference. The only thing left was the HEI! I pulled it and cleaned everything real well. I replaced the module with a high performance one and started to put it back when a buddy came by and looked at what I was doing and asked, "did you replace the vacuum advance?" I had not so we went to the parts house and got one. I installed it and replaced the rubber parts if the vacuum line, set the timing. When I hit the key, the engine, the engine started before it turned over once and ran so smoothly that I was amazed. I reset the idle and took it around the block and it really preformed well. Problem SOLVED!
The moral of this is the HEI is the best distributor for almost anything and even an HEI needs service sometimes. If you have to get a vacuum advance, get the 10 degree one for trucks. They are exactly the same as the V-8 part, as is the module.
best wishes,
Les
