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| Quadrajet secondary actuating rod [message #353360] |
Tue, 31 March 2020 09:31  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Anyone with access to a carb willing to send me a measurement? Or know of a published spec for the secondary actuating rod? 1. the length of the actuating rod from primary end tip to front edge over secondary end (top). and 2. the length of actuating from primary end tip to the front edge of secondary end down at the bottom, near the bend of the rod.
Here is a pic of the secondary end of what I would like you to measure. Above his finger, front side of rod where it hits the tang (to the primary end), and below his finger where the front edge of the rod sits in the slot (to the primary end of the rod).
http://www.gmcmhphotos.com/photos/cadillac-500-throttle-linkage-modification/p3996.html
It's easier to measure the bottom with the carb off, but even if you can only get a top measure that would help.
If you want to read a longer "why" keep reading...
My 1975 always got worse than expected mileage (6-7 with 3.42 gear and no toad). Comparing the secondary actuating rods, I realized mine is off on the actuating, and return. But the sheet that comes with a carb kit only says "bend tang" to adjust and my Doug Roe quadrajet book only says "don't overdo it". I'm thinking in 45 years the rod got bent, intentionally or otherwise. At idle, it does not even hold the secondaries shut.
I have five quadrajets I can put my hands on with a donation, junk, local friend, and my two. Top measurement on this rod has a 1/8 inch variation (about 3.2 inches), while the bottom measurements are closer to each other (about 3.07).
Thanks
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
[Updated on: Tue, 31 March 2020 09:35] Report message to a moderator |
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| Re: [GMCnet] Quadrajet secondary actuating rod [message #353365 is a reply to message #353360] |
Tue, 31 March 2020 11:20  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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You better re-read your SPECIFICATIONS for the MOTORHOME quadrajet. That
carb has non standard secondary jets, as well as metering rods, and vacuum
pull-offs as well as spring adjustments.
Kinda reminds me of the story about two farmers discussing the cost of
operation of their respective farming operations. One, a progressive,
forward thinking person, expoused the concept of modernizing his operation,
with tractors and mechanized harvesting equipment.
The other farmer still clung to the old school ways of draft animals
and horse drawn harvesting equipment.
The progressive farmer noted that in laying-by times, his equipment
was content to just sit, not burning any fuel, or requiring any currying or
horse shoeing like livestock owned by farmer #2.
Farmer #2 lamented that when his horse teams and mules were not
working, he reduced their oats and hay rations. One of his mules, when put
on short rations, up and died from starvation, and the farmer complained
that just about the time he had his feed costs under control, his stock all
were starving.
What does this have to do with GMCs you might ask?
Those large secondary jets, and narrow jet needles are fitted to the
motorhome for good reason. It is a heavy vehicle, with very tall final
drive gearing. When you exceed 55 miles per hour in one, and push a bunch
of air in front of the coach, you compensate by feeding the engine more of
the swill that passes for gasoline these days. That mitigates the heavy
loading.
If you lean that carb out just a bit too much, your mule might just up
and die on you like farmer #2.
Just saying!
Jim Hupy
Salem, Oregon
On Tue, Mar 31, 2020, 7:32 AM Tyler via Gmclist
wrote:
> Anyone with access to a carb willing to send me a measurement? Or know of
> a published spec for the secondary actuating rod? 1. the length of the
> actuating rod from primary end tip to front edge over secondary end (top).
> and 2. the length of actuating from from primary end tip to the front edge
> of secondary end down at the bottom, near the bend of the rod.
>
> Here is a pic of the secondary end of what I would like you to measure.
> Above his finger, front side of rod where it hits the tang (to the primary
> end), and below his finger where the front edge of the rod sits in the
> slot (to the primary end of the rod).
>
>
> http://www.gmcmhphotos.com/photos/cadillac-500-throttle-linkage-modification/p3996.html
>
> It's easier to measure the bottom with the carb off, but even if you can
> only get a top measure that would help.
>
> If you want to read a longer "why" keep reading...
>
> My 1975 always got worse than expected mileage (6-7 with 3.42 gear and no
> toad). Comparing the secondary actuating rods, I realized mine is off on the
> actuating, and return. But the sheet that comes with a carb kit only says
> "bend tang" to adjust and my Doug Roe quadrajet book only says "don't overdo
> it". I'm thinking in 45 years sthe rod got bent, intentionally or
> otherwise. At idle, it does not even hold the secondaries shut.
>
> I have five quadrajets I can put my hands on with a donation, junk, local
> friend, and my two. Top measurement on this road has a 1/8 inch variation,
> while the bottom measurements are closer to each other.
>
> Thanks
>
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: Quadrajet secondary actuating rod [message #353368 is a reply to message #353360] |
Tue, 31 March 2020 12:12 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Jim,
Thanks for your reply - do you have a link to share of any GMC specific tuning specs beyond OEM manual pages 6M21-25 I already have? The secondary rod specs there are for gaps and say "bend the tang" to adjust. That assumes a standard rod shape/length. I am not trying to lean it out, change the jetting, or anything else... I have not found a reference point for the specific rod I asked about. I would welcome a measurement from you if you have a good running carb.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] Quadrajet secondary actuating rod [message #353370 is a reply to message #353368] |
Tue, 31 March 2020 12:32 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Tyler, I can do that for you, but, a far better authority than I am is Dick
Paterson. He has a website, Springfield Ignition googled will find it. He
is an absolute master with motorhome quadrajet carbs. Try him first, he is
a great guy, and a good friend. Owns a GMC to boot.
Jim Hupy
Salem, Oregon
On Tue, Mar 31, 2020, 10:16 AM Tyler via Gmclist
wrote:
> Jim,
> Thanks for your reply - do you have a link to share of any GMC specific
> tuning specs beyond OEM manual pages 6M21-25 I already have? The secondary
> rod
> specs there are for gaps and say "bend the tang" to adjust. That assumes a
> standard rod shape/length. I am not trying to lean it out, change the
> jetting, or anything else... I have not found a reference point for the
> specific rod I asked about. I would welcome a measurement from you if you
> have
> a good running carb.
>
>
> --
> 1975 Glenbrook, 1978 Royale rear bath
> Raleigh, NC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: Quadrajet secondary actuating rod [message #353371 is a reply to message #353360] |
Tue, 31 March 2020 12:48 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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On secondary throttle lever that tang up top is what starts to open the secondary throttle at a reduced rate. Then it uses the bottom pivot to open rapidly during last few degrees of primary rotation. Your problem may be with the primary rocker plate that "floats" until like 45 deg rotation. Perhaps that is installed wrong as there should be no tension on secondary throttle
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Tue, 31 March 2020 12:54] Report message to a moderator |
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