Tuning the car this weekend (L-72) or at least trying to!!..checking all the basics, dwell gap timing etc. WHile checking the timing, noticed there is no vacumn at idle only when the motor is revved and this is for the distributor and the vacumn advance..is this right?..always thought that the distributor got manifold vacumn not venturi vacumn...once the motor is revved a little the advance comes in but along with the mechanical advance as well giving me way too much advance.55-65 degrees+. Could there be a problem in the carb?? wrong gasket..missing parts etc.??..how could the vacumn be wrong at the port??. Carb was rebuilt/restored..any ideas?? Thanks

Albert

In '69 it should be manifold vacuum, not ported. The only thing I can think of is you connected the distributor vacuum line to the wrong vacuum fitting on the carb. Sometimes the location is deceptive. A low fitting can be internally connected to port (above the throttle plates) and vice-versa. Check the different vacuum fittings on the carb with a vacuum gauge. You should get about 12 inches of manifold vacuum at idle with that engine.

Actually in 69 it is ported. Hook the line into the choke pull off with a tee everything will be fine.

Specs from '69 Chevy Service Manual for 396-375 dist part no. 1111499: centrifugal advance 0* @ 900 rpm, 9* @ 1250 rpm, 17* @ 2000 rpm, 32* @ 5000 rpm; vacuum advance 0* @ 6" Hg, 15* @ 12" Hg, Initial 4* BTDC at idle. I don't see how those specs could work for ported vacuum advance.

Actually in 69 it is ported. Hook the line into the choke pull off with a tee everything will be fine.

I wish it was that easy. The line is part of a steel line and hose that goes from a specific port to the distributor..its done that way in the assembly manual..The way the dist. is set up is for manifold vacuum as it did work off the choke temporarily.could the carb maybe have a incorrect metering block or base plate?..would it make a difference??..never checked those numbers.."assumed" they were correct pieces. Need to find a carb expert I think. Car runs/idles good with 40 degrees of advance enough for now. This may take some time to figure out.

ALber

On page 6M-41 of the '69 Chevy Overhaul Manual is a picture of the '69 Holley carb. The vacuum fitting on the low passenger side front that is at about a 45 deg angle is decribed as "manifold vacuum". The one that comes straight out the pass side bottom and points to the pass side is described as "canister purge signal tube (RPO NA9)". The one that angles out from just under the air cleaner flange is described as "TCS clean air tube".

Numbers are numbers it doesn't pertain to where or what the vacuum source is.

Specs from '69 Chevy Service Manual for 396-375 dist part no. 1111499: centrifugal advance 0* @ 900 rpm, 9* @ 1250 rpm, 17* @ 2000 rpm, 32* @ 5000 rpm; vacuum advance 0* @ 6" Hg, 15* @ 12" Hg, Initial 4* BTDC at idle. I don't see how those specs could work for ported vacuum advance.

They are just that, specs, without regard to whether it is hooked to ported or manifold vacuum as Mike indicated.

On page 6M-41 of the '69 Chevy Overhaul Manual is a picture of the '69 Holley carb. The vacuum fitting on the low passenger side front that is at about a 45 deg angle is decribed as "manifold vacuum". The one that comes straight out the pass side bottom and points to the pass side is described as "canister purge signal tube (RPO NA9)". The one that angles out from just under the air cleaner flange is described as "TCS clean air tube".

Is that for the L72 engine/4246 Carburetor?