non functional secondaries on Quadrajet

R

rgogan

New member
Sep 20, 2004
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Spent an hour watching a video about trouble shooting the Rochester Quadrajet secondary problems. What an eye opener!!

Checked my GMC quadrajet #7043254 that had been rebuilt several years ago and installed by me following detailed instructions from the rebuilder. Was
never happy with the performance, but the rebuilt card had undergone dyno testing and 3 gas measurements so I figured this would be as good as it
gets.

Found the Single hole carb to intake manifold gasket supplied was interfering with the opening of the secondary butterflies. Butterflies were only
opening about 10 degrees of normal 90 degree rotation. Could even see the wear marks on the gasket looking down through the throat.

Removed the gasket and removed the interfering areas and reinstalled the carb and gasket being very careful to follow the torque sequence and values
in the maintenance manual. Was delighted to see full 90 degrees of opening when I worked the butterflies from the carb mechanism. I was expecting a
big jump in performance.

However, when I floored the accelerator pedal, the butterflies opened only 10 degrees again. The accelerator cable has been stretched from all the
years of pulling against secondary butterflies with restricted excursion. Will talk to my rebuilder today about the damage to the accelerator cable.
Looks like about a $100 item from various suppliers.

Also, raw fuel was seen inside the intake manifold when the carb was removed. When I looked at the styles of the carb to intake manifold gaskets
available in rebuild kits, only two styles are available: 4 hole or 3 hole. The one supplied to me originally had only one huge hole. I am wondering
if my one hole design is not properly blocking some passage on the underside of the carb causing fuel to dump into the intake manifold. I suppose the
float could be stuck and the fuel bowl overflowing but would it leak into the intake manifold? Most of the gas was pooling on the passenger side of
the intake manifold. I never checked the underside anatomy of the carb when I had it off to see if a passage should have been sealed off by the proper
gasket. After watching the video, I am only a secondary butterfly expert.

Thanks for your assistance. I am in awe at the carb knowledge displayed by posters on this forum and know that a properly functioning quadrajet is the
closest carb to fuel injection performance out there. However, I am being drawn to the fuel injection option to eliminate some of these potential
screwups.
 
Sometimes simple bending of some parts will allow the full travel of the trottle cable. The gas pedal itself, and I cant remeber where on carb. My
gmc is still snowed in to look.

The gas could be plug holes letting loose? Most people epoxy them closed.

Only other thing I can add- is i have a gmc spec carb on my workbench to rebuild. I picked up a kit for it from quadrajet parts.com to get the
best/correct kit i could find. . As i believe not all quadrajet carb kits are the same.
--
Jon Roche
75 palm beach
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
Good thought about plug holes. Will need to get some detailed views of where the plug holes are before I start JB welding holes shut.
Let me know what Carb to intake manifold is the proper one when you are ready to remount your carb.
 
Try bending your gas pedal linkage out to get some more travel.
If that doesn't work you can clip some fishing weights on your throttle cable to shorten it up a bit and that will fix your problem.
--
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
 
That sounds like a good plan. I was skeptical that a braided steel cable could stretch that much and it seems more likely the accelerator pedal
linkage to the cable bent out of shape from the pressure and bending it back to original specs should solve the problem.
 
I just looked up the rebuild date. It was 2004. I have been driving on basically only the primaries since that time. No wonder I was downshifting up
just about every substantial hill. Probably, the only think that saved me worse loss of power was that my rebuilder rejetted my primaries to #73's
because back then I was running manifolds instead of headers and they were cracking from the heat of the engine running lean. Might have to put the
OEM #70's back in now that the secondaries are functional. Might help my gas mileage.
 
Found some additional information on the carb to intake manifold gasket. I pulled the old shipping box from the attic that was used for the old carb.
It had the original gasket in it that had been removed when the carb was sent in. I am only the second owner and purchased the GMC at 60000 mi from
the original owner. I presume the carb had never been removed during that time and the gasket I am looking at was the OEM. The gasket has one huge
hole only outlining the outward parts of the primaries and secondaries. There are no webs between the bores. There is even more gasket material
missing from the front area of the primary bores compared to the one the rebuilder sent me. If the factory used such a skimpy gasket, I guess there
is no need for the fuller coverage gaskets that are in rebuild kits. I might be missing something here and would be delighted to here some expert
feedback.
 
Errrr, Roger, Rich, Rick, Romeo,

You aren't signing with your first name, so I take the leap of reasoning that your first name begins with R.

I guess I feel goofy addressing this to a computer rather than a person.
:p

I'm not an expert but I do remember a couple or three times where an expert was driving a carbureted GMC to diagnose it, and noting no "waaahh" sound
on flooring it, reached down and pulled up on the gas pedal, and the problem with non-opening secondaries was fixed while the coach was rolling. Now,
that offends my sensibilities because there was no corrective action to make sure it didn't happen again, unless the linkage work-hardens being bent,
and won't bend back because of that. However, it may not hurt to try that. The fishing weights are applied at the pedal end of the cable, I think.
Slightly lighter return spring might help, but that's a little like being a test pilot, where if it allows the carb to stick wide open, it could be
ugly.

I agree that perhaps the gas is coming from those plugs. A number of times in this forum, the JB Weld fix has been mentioned and never a mention of
failure. I don't think you have big problems, especially since the coach has been running smoothly rather than powerfully all those years. Thanks
for the tip on altering the jets when putting on exhaust headers.

Carey
--
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
 
I made the mistake of not quoting the thread to keep the rest of the forum that gets only emails oriented as to what was the topic.

I was responding to Rgrogan about his problem with Quadrajet secondaries not opening more than about 10%. He thought that maybe there was a leak in
his carb because there was gas pooled inside the intake manifold just under the carb. My edited quote is below:

I guess I feel goofy addressing this to a computer rather than a person.
Razz

I'm not an expert but I do remember reading a couple or three times on this forum, where an expert was driving a carbureted GMC to diagnose it, and
noting no "waaahh" sound on flooring it, reached down and pulled up on the gas pedal, and the problem with non-opening secondaries was fixed while the
coach was rolling. Now, that offends my sensibilities because there was no corrective action to make sure it didn't happen again, unless the linkage
work-hardens being bent, and won't bend back because of that. However, it may not hurt to try that. The fishing weights are applied at the pedal end
of the cable, I think, if you would rather go that way. Slightly lighter return spring might help, but that's a little like being a test pilot, where
if it allows the carb to stick wide open, it could be ugly.

The gas leakage fixable by the JB Weld ends up on top of the manifold if I am correct. A number of times in this forum, the JB Weld fix has been
mentioned and never a mention of failure. So, therefore, it's up to you whether you want to JB Weld those plugs closed. Maybe when taking the carb
off, the accelerator pump actuated and squirted gas down into the manifold. Thinking about it, if you actuated the secondaries as a test, quite a lot
of gas would have been pumped right into the manifold. If it runs well, I don't think you have big problems, especially since the coach has been
running smoothly rather than powerfully all those years. Thanks for the tip on altering the jets when putting on exhaust headers.

Carey
--
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
 
The 4 hole QJet gasket is correct. Some gaskets have and additional cross over passage in front and some do not depending in the division the carb
was used in. The fuel pudding may just be from you messing with linkage and accel pump. Normal. I bent the bracket that to goes to manifold to the
rear of coach for more pull to vertical.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
If the wells are leaking the typical symptom is the fuel bowl emtying and the carb flooding after sitting. many rebuilders epoxy those wells as part
of the rebuild. Its a known trouble area on QJ carbs and if you have it off and see it isn't done already, break out the JB weld. {clean well with
carb cleaner first]

Another posssible source for thhe puddlingfuel? There are two large wedd just before the seconarys. THese are linked to t small holes at the front of
the secondary air valve, and serve as an" accelerator pump " shot by syphoning fuel as the valve opens, preventing a stumble on rapid acceleration. If
you blipped it upen a few times, it may be pretty wet from that

Another option on the cable is to lookat adjustable aftermarket throttle mounts. May require a bit of tinkering but should work to get the travel
needed.

Also, if you are having cable issues, check to make sure the trans kickdown switch is engaging

--
76 Glenbrook
 
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