Dave,
This is a posting from Jon (The Carburetor Shop) on the stovebolt site from
last year that may help with the leaky Rochester problem:
(Posting from "Carbking" http://www.thecarburetorshop.com/ on stovebolt.com
forum)
Had Rochester only used 8 screws instead of 4 to hold the airhorn/bowl cover
to the bowl on the B series carburetors, this would not be a problem. As
they didn't, warpage from heating/cooling cycles causes an internal vacuum
leak in the passage controlling the power valve, causing it to stay in the
open position (too rich).
Double gaskets MAY work for awhile, but will hasten better repairs.
The procedure we use is very time-consuming, but also very simple and I will
post here for do-it-yourselfers.
First obtain some scrap iron plate at least 3/8 inch thick. Drill holes in
the plate to align with the airhorn/bowl screws; also machine the plate so
that it can be placed flat on either the bowl or the air horn (or use two
plates).
Now, screw the airhorn to the plate (snug, but do not tightened. With a
feeler guage, measure the clearance between the airhorn and the plate. Take
another plate and place on top of the airhorn; and using a rather
sophisticated fixture (C-clamp), clamp the two plates together, squeezing
the airhorn. Tighten the C-clamp to remove 0.003 inches; NO MORE. Set the
assembly in an oven and heat to 400 degrees F. Allow to cool naturally. When
cool, the C-Clamp will probably be loose. The heat and tension reverse the
warpage process. Repeat until warpage is gone. Repeat for the bowl.
Of course, in another 15 years, the problem will return.
Filing or milling the castings flat obviously removes metal, and the repair
will be very temporary, and ruins the castings for proper repair. Best to
take the time and do it right the first time.
Oh, one other thing, best to NOT use the oven belonging to your significant
other!
Jon.
Larry Kephart
1955 1st 3100 Chevy (BillyBob)
1991 Jeep Wrangler (Renegade)
Boca Raton, Florida
e-mail: webmaster@laroke.com
http://www.laroke.com/larryk4674/1998/billybob.htm
-----Original Message-----
From: owner-oletrucks@autox.team.net
[mailto:owner-oletrucks@autox.team.net]On Behalf Of Dave
Sent: Tuesday, January 27, 2004 1:57 PM
To: oletrucks@autox.team.net
Subject: [oletrucks] Re: Leaking Rochester 1bbl. Any cure?
Hi:
It's Dave with my son Dusty's 1950 GMC 1/2 ton. We just rebuilt the head on
the 235 six in the truck and got a replacement rebuilt carb from BFCI in
Burbank. As soon as we bolted it together and idled the motor for several
minutes, the main body gasket began getting moist and slightly seeping.
This is the THIRD remanufactured carb we put on here. I checked the fuel
pump pressure - 6 lbs. Shouldn't be too excessive for a brand new needle and
seat. I spoke with Jim Carter's about it, and they admitted that most of the
remanufactured carbs they sell will leak there too. Almost ever one of those
old carbs have been rebuilt several times already, and over-tightened and
warped slightly at the mating surfaces. This allows those leaks.
Any solutions, short of sealing it up with JB Weld??
Also - who makes the best door rubber seals that FIT? The set we installed
during restoration (can't remember which catalog we ordered them from!) are
too thick and the doors don't close all the way flush. And they never
compressed as promised.
Thanks,
Dave Destler
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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