I've got a '71 800b all wheel drive with a 304. After sitting around for a couple of months it developed a problem in which, after running for about 15 seconds, it would rev itself up and cut off. I had the carb professionally rebuilt and tuned to factory specs, but it still did it. I've been told that its a vacuum seal leak. However, no one has offered any suggestions on how to find in and fix it. I can do most all work on my scout but I don't want to start taking apart a 30 year old engine unless I know what I'm looking for. Any suggestions?