As I am running Rochester's, yes, I have drilled the holes out (modified the
off idle circuit(s)). Plugs eventually go back in (a lead plug on the
inside and an aluminum plug on the outside, if I remember correctly), or
you'd have bad gas/vacuum leak(s). The tech article is pretty good (but
brief) and there is a companion one out there running around too that is
also good. Can't remember where I got it, but it's floating around, perhaps
from Inliner's International (and it discusses this circuit vacuum vs.
manifold vacuum stuff) or maybe from Pat directly (he's *very* knowledgeable
and a pleasure to speak with). Be very careful and very patient or you'll
ruin a perfectly good Rochester in one pass of the drill ("hole" size will
vary depending on your manifold, carburetor, cam, and head porting). The
modification is the difference between night and day with multi carburetor
intakes and results in some nice torque off idle into your power range (and
some good neck snap off idle). It's fun!
Allen in Seattle
'50 3100
----- Original Message -----
From: "William M. Schickling" <wschick1@twcny.rr.com>
To: "Allen Jones" <jonesal@u.washington.edu>; <oletrucks@autox.team.net>
Sent: Sunday, December 10, 2000 3:31 PM
Subject: RE: [oletrucks] vacuum advance / lines
> Allen,
>
> I printed out a couple pages from the web (Sorry, I'll have to go look up
> the URL) from someone that describes the modification your are talking
> about. First you knock out some plugs then drill out the remaining holes.
> Alright, I went and found my print outs.
>
> It's an Inliners article from a Pat Smith, called: Improving Driveability
> with Multiple Rochesters.
>
> http://www.inliners.org/tech/tech4.html
>
> Pretty informative, but only talks about the carbs. Have you drilled the
> holes out ? Do the plugs go back in or do they stay out ?
>
> Bill
>
> -----Original Message-----
> From: owner-oletrucks@autox.team.net
> [mailto:owner-oletrucks@autox.team.net]On Behalf Of Allen Jones
> Sent: Sunday, December 10, 2000 3:58 PM
> To: oletrucks@autox.team.net
> Subject: Re: [oletrucks] vacuum advance / lines
>
>
> 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
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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