I'm not sure I agree with that. With two carburetors, vacuum at the port at
the base of the carburetor(s) will drop way off and you won't get near the
advance you need. I highly recommend going with an advance line directly
off the manifold. That's what I did with my Offenhauser dual set up, and
unfortunately, I still don't get as much advance as I'd like (with either my
HEI or the stock distributor w/ new advance bell). But to answer your
question, yes, a vacuum advance dist is preferred. Also, because you won't
be drawing near the volume of air through the carburetor, you will, in some
cases, need to modify the low end circuits so that they deliver enough
gasoline. As an example, if running dual Rochester's, you will need to
drill out the off idle orifice so that there is no hesitation (because of
low vacuum, and hence not enough petrol). Regarding the Mallory, it depends
whether you're running dual point vacuum from the old days (acceptable
units), pure mechanical advance (troublesome), or newer vacuum advance
Mallory dist (won't touch 'em).
Good luck!
Allen in Seattle
'50 3100
----- Original Message -----
From: <Passnb4U@aol.com>
To: <wschick1@twcny.rr.com>; <oletrucks@autox.team.net>
Sent: Saturday, December 09, 2000 6:33 PM
Subject: Re: [oletrucks] vacuum advance / lines
> In a message dated 12/9/00 5:32:40 PM Pacific Standard Time,
> wschick1@twcny.rr.com writes:
>
> > List,
> >
> > My winter project is to rebuild a 235 for my truck. I am putting a dual
> > intake manifold on and was wondering about the vacuum lines. each carb
has
> a
> > spot for a vacuum line and the manifold has a spot for one as well. Is
it
> > better to plug the carbs and run a line from the manifold ? Or try to
> > connect both carbs up to the vacuum advance ? I have seen on either
the
> > stovebolt or inliners page that keeping a vacuum advance, even with
dual
> > carbs is the preferred setup. Is this true even with the Mallory dual
point
> > or hei distributors ?
> >
> > Any and all feedback welcome.
> >
> > Bill Schickling
> > 1940 3/4 Ton
>
>
> You'll want to use one off the carb' ported vac., assuming you're using
an
> original type distributor.
>
> If you use intake vacuum, then intial advance will be too much, and
you'll
> get part throttle pinging...and if you set the timing back to compensate,
> your total advance will be too low for any mid to upper RPM use.
>
> Mike
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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