drwet

The other day my '79 383 TH700R4 started running rough. A/F gauge tells me its running lean. Obviously the causes for this are not enough fuel or too much air. I've given the carb a once over and I don't think its a fuel supply problem. That leaves a vacuum leak. I don't have a lot of vacuum connections on my motor so it should be simple to figure out. The most likely culprits are the vacuum to the headlights and cruise control, and the vacuum to the power brake booster. I've tried disconnecting both these circuits to see if one of them is leaking. Problem is the condition is not consistent enough for me to be sure. Has anyone ever had a power brake booster start leaking and cause a similar condition? (The brakes work fine.)

C6DuffMan

The booster in my 71 was leaking. Brakes worked OK, but not great. You should get 2 - 3 good brake pumps with the engine off, if the booster is good. You can also check it using a MightyVac.

Mariana

Did you check the rubber grommet on the booster? Also, I had that problem and replaced the grommet and bled the brakes in sequence. Come the find that it was the rear passenger caliber that had the smallest leak. It never dripped but it was a lil wet. It was already so tight I was scared to tighten it any more but i tightened it the smallest bit and it went away. bled the brakes again and problem solved.

drwet

Update: I checked all the vacuum lines for leaks and the headlight system is not holding vacuum. I disconnected the headlight vacuum line and plugged it. Car ran great. Now I guess I just have to go through the headlight vacuum system and figure out where the leak is.

MakoJoe

Most of the vacuum lines come from a common point in the system. It helps to have a vaccuum pump to test each line from the vacuum fitting on the intake manafold. If one part is leaking it can cause other problems.

here is what that fitting looks like

http://www.ecklerscorvette.com/corve...1968-1982.html

Check each of the lines coming off of this and you will probably find a cracked hose somewhere in the system.

Vacuum line kit for the head lights and other parts

http://www.ecklerscorvette.com/corve...1973-1979.html

Peterbuilt

Here's a guide if you need it.
http://www.corvette-101.com/vacuum.htm#top