Amc 360 Vacuum Advance

My 360 in the 77 CJ7 has the vacuum advance hooked up to the carb below the throttle plates. I always thought the vacuum advance would be above the throttle plates? That is how the 225 V6 is in Snowshoe. I don't see a port anywhere else besides the intake manifold itself. Carb is motorcraft 2100.

 

The factory had the vacuum advance hose hooked to ported vacuum at the carb. Later year V8s ran ported to the spark CTO switch. Ported vacuum came out of emissions regulations. The goal was to use the throttle plates to block off the vacuum at idle. This would retard the timing at idle causing the combustion chamber to run hotter and reduce emissions at idle. If its running fine at full vacuum I would keep it as is.

 

I'm not going to get into a discussion here, but, ported vacuum has been around looooooong before any emission controls.

The consensus of the conversation I had with various folks is poor manufacturing tolerances coupled with variations in fuel grades caused unstable idles under vacuum advance. The cure was to run zero advance at idle.

Ported vacuum is in front of the choke housing down on the bottom.

 

Either way is a compromise. Like Chuck said, if it runs good on manifold, leave it. That is why emissions used a temp controlled switch if you will,
for vacuum control. You do get a cooler running engine at idle with manifold vacuum. Off idle , the vacuum present is the same. Glad you could point
out the location of the port.

 

That is where it is hooked up too, so I guess I am good then. Thanks!

 

So if you are getting vacuum at the ported nipple at idle, your plates are open too far. This can be caused by idle mixture, timing, amongst other issues.