Cranking Vacuum

[John T.]

What would be the expected cranking vacuum on a 1962 250 HP 327 ?

Any thoughts are appreciated.

John

[Duke W.]

Re: Cranking Vacuum

It would be highly dependent on cranking revs and throttle position - on the fast idle cam for a cold start? On the curb idle stop with no manual opening of the throttle?

A hot start with the throttle at least one-quarter open will generate only very low manifold vacuum and virtually no signal at the venturi, which is why at least half throttle is proper for "unloading" a flooded engine and is often necessary on carbureted engines due to fuel percolation that creates an over-rich condition in the manifold.

Duke

[John T.]

Re: Cranking Vacuum

Trying to diagnose a "no start" problem Cold engine, throttle closed, all vacuum ports plugged.

Is there a ball park vacuum figure I should expect ?

Thanks

John

[John H.]

Re: Cranking Vacuum

Trying to diagnose a "no start" problem Cold engine, throttle closed, all vacuum ports plugged.

Is there a ball park vacuum figure I should expect ?

Thanks

John

John -

Lots of variables involved, which is probably why no such spec has ever been published.

[Jim L.]

Re: Cranking Vacuum

I'd expect the cranking vacuum signal to be no greater than 3" Hg, and probably less than 1" Hg.

Jim

[Clem Z.]

Re: Cranking Vacuum

this is why you need the choke to close fully to cause a high vacuum in the carb venturi area so fuel will flow thru the boosters from the float bowl to start a cold engine..

[Bob H.]

Re: Cranking Vacuum

how about details such as what you have done so we can maybe come up with some fix?