I have a bb402 that I just put some aluminum edelbrock performer heads on to upgrade my iron ones. After installing the heads I noticed that while driving above about 25% throttle I would hear a sort of whistling sound out the exhaust, but this was only under heavier throttle than cruising. Another new issue to the new heads was that I had trouble shutting down the engine. It would always kind of sputter a few revolutions before actually stopping like it was dieseling or something. I do have a vacuum guage in the cab that I monitor regularly, and at idle I would have 15in, and if I downshifted while driving to use engine braking to pull the rpm's up it would go up over 20in.
Well, this weekend I was out and all of a sudden I noticed a major idle problem where it felt like it was going to stall every time I came to a stop, it never actually did stall but just barely. My vacuum at idle was barely 10in, and if I got up to speed and downshifted to pull up the rpm it would only get up to 15in. So basically I lost 25-35% of my vacuum all at once. I was hoping a vacuum line came loose but unfortunately that was not the case.
I'm thinking maybe I made a mistake when adjusting the valves, which is why I had strange whistling and shutting down issues, and that maybe this weekend something happened to a valve or lifter that made the problem worse and my valves are not closing properly?
I have a hydraulic flat tappet and I followed standard procedures when adjusting them.
Also, this weekend the shutting down problems were much worse, it would sputter for a solid 5 seconds at least and then finish off with a big puff up through the carb.