1977 coupe deville 425 manifold vacuum behavior

Thanks for your response Shep.

manifold vacuum not to be as robust as it once was. Must be valves get worn and don't seal as well etc.

I just wonder now if a much lower cold engine manifold vacuum is normal. I'm envisoning that as the engine warms up the metal parts expand slightly improving the vacuum seal to the outside. Is this normal on an old engine.

With a cold manifold vacuum of 14 in Hg seem low for a 425 cid with 100 thousand miles on it.

Thanks again for your helpful response....I ain't no mechanic. Any hints are very welcome.

Later, Tich

Shep,

Forgot to answer the performance question. I've had the car about a year and put on a thousand miles or so. It ran shitty from the get go but really crappy before I parked it about 3 months ago. The plugs were undergapped about 10 thousands and very carbon fouled. Found the air fuel mixture screws all "screwed up" if you'll pardon the expression. The right screw was backed out from lightly seated about 1 1/2 turns and bent. The right screw was about 4 1/2 turns. The curb idle was 125 RPM higher than it should have been also. I think after putting 126 bucks worth of parts on it it will run fine. Just waiting for a combination valve to repair the brakes. The only reason I bought this old Cadillac was for the 100 inch front seat wide enough for grandma's butt to take her to appointments :-) Previously, I was having to rent a car twice a week!

Thanks for your post.

Later, Tich

That's probably not what's going on. A cold engine is much less efficient than a warm one. Its basically "loaded" by thicker oil and less efficient combustion (plus an over-rich fuel mix thanks to the choke being applied in a carbureted engine such as yours.) Take that added load off, and the vacuum increases. Perfectly normal.