IIRC there is a # stamped on the arm of vac can IIRc you get about half that # in mech advance. so you can search out a can that will give the advance needed.
my understanding is with a stock dist on ported vac it adds to much mech advance. up to 50* or more.
the can is adding mech advance and the weights are adding more mech advance when rpm increases.
I tried last night to swap it onto ported and the results were poor.
I removed can from full vac, rpm drops, adjust back up to 750 curb idle, hook line to ported vac, adds no mech advance, test drive and 1/2 throttle from stop it pings and spark knock.
change back to full vac on can and adjust curb idle back down to 750, test drive, no ping or spark knock.
dist & carb working together may be what I stumbled upon on mine.
on my junk, following the steps in Don's book and not the way I have always done it fixed a lot of things I have put up with for yrs.
I will be hooking up the vac gauge on ported vac to see what it is doing at 1/2 throttle from a stop. and get a WOT reading.
That's very interesting that it pings at part throttle with ported vacuum and does not ping on manifold vacuum. In theory ported is manifold vacuum but its port is above the throttle blade. I would like to know how much vacuum yours pulls at part throttle on ported and manifold vacuum. Actually at 1/4 to 1/2 throttle both ported and manifold vacuum are still pulling a good vacuum. When we used to test for plugged exhaust systems we would watch the manifold vacuum at idle and then raise the rpm to about 2000 rpm in park with the eng under no load and normally the vacuum will actually increase a little bit and hold that. If it did not increase any and started dropping then we would look for a restriction in the exh system.
I wonder if as CAB pointed out that because of where the ported vacuum port is in the carb it gets a slightly stronger signal at part throttle as both ported and manifold vacuum should drop to 0 at WOT. And maybe the ported port is high enough in the carb throat that it may pick up a little venturi vacuum which gets stronger with more throttle ?
Please let us know what your vacuum readings are if you get to take them as it has me curious of why it pings at part throttle on ported and not on manifold vacuum ? Thanks , Ron
