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Vac advance - dumb question....

Posted: Sun Apr 28, 2019 11:51 pm
by KevinW
Went for first legal OTR drive today but had left the vac advance hose un-plugged from the dizzy.
I didn't detect any difference in engine performance.
But no vac advance on ignition timing, and the Holley sucking more air than it should from the ported vac feed.
Would this result in greater petrol consumption? Any other effects?

Re: Vac advance - dumb question....

Posted: Mon Apr 29, 2019 2:25 pm
by peterc
With the carb sucking more air it would have been running weak and if it had been tuned with the vac pipe connected then not desirable from the engines point of view. Not having the vac on the dizzy is less of an issue. Some engine tuners suggest not having it and merely adjusting the timing to suit. They would consider it an economy device to supplement the advance weights.
Surprised you didn’t notice the effect of the open port on the carb.
Peter C

Re: Vac advance - dumb question....

Posted: Mon Apr 29, 2019 7:48 pm
by KevinW
Me too. But have also now learnt I had connected distributor to the ported vac connection on the Holley, so it wasn't sucking full vacuum anyway.
Need to make this swap and try again.

Re: Vac advance - dumb question....

Posted: Sat May 04, 2019 8:20 am
by amulheirn
Speaking to Al at Thunder Road Speed Shop, he said he commonly removes vacuum advance from cars like ours because they're so light they don't need it. Nice side effect is that setting up the timing becomes easier.

Hope the first drive was fun Kevin!