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Re: [GMCnet] Carb / Vacuum issue [message #288666 is a reply to message #288595] Tue, 13 October 2015 17:19 Go to previous messageGo to previous message
USAussie is currently offline  USAussie   United States
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma:
Senior Member
Brian,

OK, to assist you with trying to make your carb work here's some links that may help you with that endeavor:

*****************************************************************************************************************************

Provided by Bill Freeman 11/20/2009:

http://oldcarmanualproject.com/manuals/Carbs/Rochester/QJet/index.htm

http://www.newagemetal.com/pages/GMC/73-78GMC.pdf

*****************************************************************************************************************************

Provided by David Orders 9/23/2013

Tiny URL: http://tinyurl.com/pfjna85

Full URL:

http://www.amazon.com/Rochester-Carburetors-Doug-Roe/dp/0895863014/ref=sr_1_1?ie=UTF8&qid=1379874674&sr=8-1&keywords=quadrajet+hp+bo
oks

*****************************************************************************************************************************

Provided by Emery Stora 4/12/2009

GM used seven different carbs for the GMC motorhome:

455 Engines:

73 and 74 GMC's had P/N 7043254

75, 76 and early 77 GMC's had P/N 7045254 and California had P/N 7045554

403 Engines:

77 GMC's had P/N 17057254 and California had P/N 17057559

78 GMC's had P/N 17058254 and California had P/N 1758559

These carb numbers can be found on the left side of the carb, stamped on the flat surface close to the secondary throttle shaft.

There is also a date code (4 digits) stamped in the same area:

73 to 76 coaches had a number starting with 70

77 & 78 carbs start with 170

Some parts used in the 170 carbs are quite different from those used in the 70. DO NOT INTERCHANGE parts between these two series.

One example is the primary metering rods. They are .080" shorter in the 170 series, they had a different taper to the rods and they
used different size primary jets.

The rods for the 70 series carbs will be stamped D-50. (7046338) I am told that this was used ONLY in the GMC motorhome carbs.

The 170 series are different.

All GMC carbs used the same secondary metering rods. These will be stamped with a CJ.

The proper power spring for the GMC is #7036019 which has an operating range from 4" to 8" of vacuum.

One problem that some people have had is the use of gaskets from an unknown kit. There are changes in the air passages in the carbs
and it is easy to install a gasket that covers an air passage hole and that will make the carb perform improperly.

The Delco overhaul kit for the 73-74 is 7046812. For the 75-76 (NOT California!) it is 17051886

*****************************************************************************************************************************

To assist other GMC owners that might be interested in obtaining a rebuilt Q-Jet from Dick Patterson here's the procedure:

1) Check your carb for the part number: 7043254, 7045254, 7045554, 17057254, 17057559, 17058254, or 17058559

2) Call Dick and he will give you instructions on how to verify that the core you have is a good core.

http://www.springfield-ignition.com/gmc-motorhome/carburation/

3) Send him the carb and he will rebuild it and send it back.

You can also contact Applied GMC:

http://www.appliedgmc.com/prod.itml/icOid/570

Cost of rebuild is $390

Cost of core is $280

Regards,
Rob M.
The Pedantic Mechanic



-----Original Message-----
From: Brian Pimm

Dick's website says he will only work on the proper number carbs, the one I have is not one of the proper numbers for the coach, so
no I haven't. between the $600 rebuild and the $300 core, I can fuel inject it for about the same or less. Plus I don't know if
there are any cores available with the right numbers. At this point I'm just trying to get this carb to work right to see if I can
tune it good enough. :(
--
Brian


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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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