With all the lines hooked up on my '72, i'm pulling only about 5 inches of vacuum. If I plug off the lines, I pull 16 inches. My cam isn't stock, 296 intake and 300 exhaust duration at .004 lift and 112 separation, so 16 inches might be okay. But 5 inches? Is that normal with all the maze of vacuum stuff on the '72?

 

"Normal" vacuum with all the vacuum-related 'stuff' connected is usually about 1" Hg less than the "baseline" vacuum--idle vacuum with all the vacuum stuff disconnected. So, you should have 14-15" Hg. Since you only have 5" Hg, you have some leaks (or one really BIG one).

Leave all systems connected, T-in the vacuum gauge, and start the car and let idle. Get a couple of 'squeeze clamps' or a small Vise-grip. Put the clamp/VG on the vacuum line just after the gauge connection with the intent of clamping off that line. Read the vacuum gauge. You should get about the same reading as the "baseline" level...about 16" Hg. Now, continue to move the clamp/VG farther downstream, clamping off the hose and taking a reading. When you find that the vacuum drops more than 1-2" Hg, you have just gone beyond the site of a vacuum leak. Check between those two clamping locations for possible leaks; use your fingers/hands/tape/etc in an attempt to seal the leak and make the reading go back to the baseline level.

That's the process. Just keep doing that, finding leaks and fixing them until you find all the big ones. You may have a connection loose or a split in a hose, or a leaking diaphragm on one or more components in the system. If you find that the leaking line goes into the interior of the car, just go under the dash [or wherever] to continue with your search process. You may need an 'assistant' to watch the gauge for you as you test the system.

Good luck!

 

Thanks, 7T1vette. I thought that was too big of a drop, but none of my books had any info. I have new lines and headlight cans, but the rest is old. Looks like hunting time.

 

I have an Electrolux...

 

What Year?

 

5" is way low, and my bet's on a bad vacuum motor diapram in the heating/AC system. A Mity-Vac tools a good one to help touble shoot this. A 112 LSA cam should be pretty decent on the street. Also keep in mind the advertised duration at .004, really doesn't mean much of anything. The real numbers at .050 tappet, and should be on the cam card and munufacturers web site.

 

My 70 LT-1 with big flat tappet cam runs 16" vacuum at idle same for my 72 LT-1 with 247 degree @ 0.050" solid roller.

 

Nothing sucks like an Electrolux!

When my engine is running well, it pulls 21-22 inches at idle. When the vacuum system was working badly, it could only pull about 16 inches because of all the leaks.

 

I have oreck.

 

20-21" here. vaccum that is!