Vacuum Advance Question

[Oilslickwillie]

First off, thanks to those who helped me with my distributor problem. My question now is hopefully not a hard one. The vacuum advance on the distributor of 302 engine has 2 places for vacuum lines. I have vacuum tubing on the center port going to carb. The port that sits on the top side of advance has a rubber cap plug blocking it off. Question, is the top port suppose to be hooked up with vacuum line somewhere to carb also. Thanks.

 

[dmsfrr]

I'm pretty sure there's more than one version of these...
Could you post a photo or two?
and any part numbers... what year is the engine & dist?
What carb is on the engine?
More info to base an answer on is a good thing.

 

[40 Deluxe]

The outer port is for vacuum advance under light throttle conditions. The inner port (closest to distributor housing) is for retarding the timing at idle to reduce emissions. There should be a decal under the hood to show proper hose routing.

 

[darrell]

40 deluxe is right on.only did it for a few years around 70 72.

 

[dmsfrr]

.... There should be a decal under the hood to show proper hose routing.

It's not that easy, it's a 302 in a '55 and could be an odd combination of parts.

 

[darrell]

i never seen anyone use the retard line except on cars that came with them and even then most were removed which i did on my 71.

 

[Gene F]

That info on post #3 is interesting. I wonder if I can retrofit a vac adv unit like that on my 1957 Dist. The carb system I have does not have vac adv ports...

 

[craig]

What kind of a carb do you have that doesn't have a venturi vac port? A '57 dist. has a straight arm out of the vac unit, where the later dual diaphram unit has a curved arm

 

[Flathead Fever]

If you have a dual vacuum advance and you plug the rear retard port on the vacuum advance it might not be able to move when the advance side has vacuum applied to it. It would be like sucking on a straw with you finger over the end. If you do decide to disconnect the retard vacuum line, plug the hose and not the port on the vacuum advance. You need to learn what the difference is between manifold vacuum and venturi vacuum. Venturi vacuum operates the advance side and I believe manifold vacuum pulls on the retard side to quickly retard the timing when the throttle is closed.