distributor vacuum line

[Zogbert]

I'm slowly fixing the pinging my truck has had since I got it a few weeks ago. '72 C10 with a 250 and a three-on-the-tree.

Timing was quite far off, and adjusting that made a big difference.

I bought a vacuum gauge, and I figured out that the rubber hoses that plug the vacuum lines were leaking. I'm not sure if the distributor vacuum line was hooked to the correct port. When I check the vacuum at the port it was hooked to, there is very little vacuum at idle (maybe 1# at 700 rpm).

It was hooked to the top port on the first picture. I've now plugged off those two ports. The bottom one of the two ports was plugged, but did leak. I've now hooked it to the port in the bottom pic, and the vacuum increased to 14#. This port was also plugged before, but leaked.

With the vacuum line hooked up, the rpm jumps to 1030, and the timing jumps from 4 to 14 degrees. Is that normal?

I've done searches to figure this out, and have looked at the service manual, but am still not sure.