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| Quadrajet problems [message #137646] |
Fri, 05 August 2011 17:59  |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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Unfortunately we left our GMC sit pretty much unused for several years. I did manage to start it periodically and let it get up to operating temps, same with the genset and roof A/C's.
This time I went to take it out for a drive and found that it stalls whenever I touch the throttle. So I pulled the carb, cleaned it and installed new gaskets, accelerator pump and inlet filter. It still bogs and tries to stall whenever I press on the pedal. I'm an adept mechanic but I'm stumped here. I've had that carb off and on a dozen times, cleaned it, blew it out, tweaked it - no change. I know I can send it off but again, I've generally competent and unwilling to simply give up. A good friend and shop owner is out of ideas as well.
The transition from idle to part open is smooth, accel pumps works well, but just beyond barely open it appears to starve for gas. Float level has been checked and rechecked. Meter rod piston rises as expected. Closed off all vac ports with no change.
Ideas?
1978 Eleganza II
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| Re: Quadrajet problems [message #137647 is a reply to message #137646] |
Fri, 05 August 2011 18:01  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Maybe fuel fliter, fuel pump, bad gas??
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Quadrajet problems [message #137650 is a reply to message #137646] |
Fri, 05 August 2011 18:11 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
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Does the engine rev normally when it's in neutral (ie no load condition)?
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: Quadrajet problems [message #137656 is a reply to message #137646] |
Fri, 05 August 2011 18:36 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
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Ken,
Might it be that the air flaps are opening too quickly, leaning it out? You can adjust the pressure on them with the spring -- and the choke pull off can be too weak allowing them to open too fast as well.
Dennis
| kwharland wrote on Fri, 05 August 2011 17:59 |
Unfortunately we left our GMC sit pretty much unused for several years. I did manage to start it periodically and let it get up to operating temps, same with the genset and roof A/C's.
This time I went to take it out for a drive and found that it stalls whenever I touch the throttle. So I pulled the carb, cleaned it and installed new gaskets, accelerator pump and inlet filter. It still bogs and tries to stall whenever I press on the pedal. I'm an adept mechanic but I'm stumped here. I've had that carb off and on a dozen times, cleaned it, blew it out, tweaked it - no change. I know I can send it off but again, I've generally competent and unwilling to simply give up. A good friend and shop owner is out of ideas as well.
The transition from idle to part open is smooth, accel pumps works well, but just beyond barely open it appears to starve for gas. Float level has been checked and rechecked. Meter rod piston rises as expected. Closed off all vac ports with no change.
Ideas?
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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| Re: Quadrajet problems [message #137676 is a reply to message #137647] |
Fri, 05 August 2011 21:12 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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| bwevers wrote on Fri, 05 August 2011 19:01 |
Maybe fuel fliter, fuel pump, bad gas??
Regards,
Bill
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Had a 1/4 tank of ethanol free, 1 year old gas. Filled it up with fresh gas...should be okay.| GeorgeRud wrote on Fri, 05 August 2011 19:11 |
Does the engine rev normally when it's in neutral (ie no load condition)?
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No, not at all, starves for gas at 1/4 throttle in park.| Dennis S wrote on Fri, 05 August 2011 19:36 |
Ken,
Might it be that the air flaps are opening too quickly, leaning it out? You can adjust the pressure on them with the spring -- and the choke pull off can be too weak allowing them to open too fast as well.
Dennis
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This is on the primaries only, doesn't involve the secondaries.
1978 Eleganza II
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| Re: [GMCnet] Quadrajet problems [message #137682 is a reply to message #137646] |
Fri, 05 August 2011 21:48 |
Ray Erspamer
Messages: 1707
Registered: May 2007
Location: Milwaukee Wisconsin
Karma: -3
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Plugged fuel pickups in the tank?? I recently had a stalling problem and when
I disconnected the gas lines behind the selector valve and blew them out, it ran
great.
Ray
Ray & Lisa Erspamer
78 Royale "Great Lakes Eagle"
Center Kitchen TZE368V101144
Wauwatosa, Wisconsin 53226
Email: 78GMC-Royale@att.net
414-745-3188
Web Site: http://ray-lisa.page.tl/
----- Original Message ----
From: Ken Harland <kwharland@bellsouth.net>
To: gmclist@temp.gmcnet.org
Sent: Fri, August 5, 2011 5:59:17 PM
Subject: [GMCnet] Quadrajet problems
Unfortunately we left our GMC sit pretty much unused for several years. I did
manage to start it periodically and let it get up to operating temps, same with
the genset and roof A/C's.
This time I went to take it out for a drive and found that it stalls whenever I
touch the throttle. So I pulled the carb, cleaned it and installed new gaskets,
accelerator pump and inlet filter. It still bogs and tries to stall whenever I
press on the pedal. I'm an adept mechanic but I'm stumped here. I've had that
carb off and on a dozen times, cleaned it, blew it out, tweaked it - no change.
I know I can send it off but again, I've generally competent and unwilling to
simply give up. A good friend and shop owner is out of ideas as well.
The transition from idle to part open is smooth, accel pumps works well, but
just beyond barely open it appears to starve for gas. Float level has been
checked and rechecked. Meter rod piston rises as expected. Closed off all vac
ports with no change.
Ideas?
--
1978 Eleganza II
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Ray Erspamer
78 GMC Royale Center Kitchen
403, 3.70 Final Drive
Holley Sniper Quadrajet EFI System,
Holley Hyperspark Ignition System
414-484-9431
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| Re: [GMCnet] Quadrajet problems [message #137685 is a reply to message #137682] |
Fri, 05 August 2011 22:07 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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| Ray Erspamer wrote on Fri, 05 August 2011 22:48 |
Plugged fuel pickups in the tank?? I recently had a stalling problem and when
I disconnected the gas lines behind the selector valve and blew them out, it ran
great.
Ray
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Carb always has plenty of fuel while exhibiting this problem. Fuel pump providing adequate pressure too.
1978 Eleganza II
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| Re: [GMCnet] Quadrajet problems [message #137716 is a reply to message #137685] |
Sat, 06 August 2011 03:58 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Ken, two things come readily to my mind. All the changes to the fuel system,
and no change in symptoms would indicate to me that the problem might not be
fuel related. I would take the cap off the distributor and check the advance
weights. I suspect that they are rusted solid, and you are not getting any
centrifigal advance. Two other possibilities might be split vacuum hoses, or
the worst case scenario, a cracked intake manifold. Hope this helps.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Fri, Aug 5, 2011 at 8:07 PM, Ken Harland <kwharland@bellsouth.net> wrote:
>
>
> Ray Erspamer wrote on Fri, 05 August 2011 22:48
> > Plugged fuel pickups in the tank?? I recently had a stalling problem
> and when
> > I disconnected the gas lines behind the selector valve and blew them out,
> it ran
> > great.
> >
> > Ray
>
> Carb always has plenty of fuel while exhibiting this problem. Fuel pump
> providing adequate pressure too.
> --
> 1978 Eleganza II
> _______________________________________________
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| Re: [GMCnet] Quadrajet problems [message #137720 is a reply to message #137704] |
Sat, 06 August 2011 05:51 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
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| Gary Berry wrote on Sat, 06 August 2011 02:05 |
Vacuum advance stuck??
Gary and Diana Berry
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Hadn't considered that! I'll check later today. Thanks!
1978 Eleganza II
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| Re: [GMCnet] Quadrajet problems [message #137721 is a reply to message #137716] |
Sat, 06 August 2011 05:58 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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| James Hupy wrote on Sat, 06 August 2011 04:58 |
Ken, two things come readily to my mind. All the changes to the fuel system,
and no change in symptoms would indicate to me that the problem might not be
fuel related. I would take the cap off the distributor and check the advance
weights. I suspect that they are rusted solid, and you are not getting any
centrifigal advance. Two other possibilities might be split vacuum hoses, or
the worst case scenario, a cracked intake manifold. Hope this helps.
Jim Hupy
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I'm right with you on looking for other sources of the problem. I did check the mechanical advance and it's all working smoothly, even had evidence of fresh lube.
I disconnected and blocked off vacuum hoses that are below the butterflies thinking the same as you...no change.
I did not consider a cracked manifold (and hate to mind you!) but I suppose I have to consider all possibilities. I've read of others having that problem but don't remember the symptoms. But honestly, I'm skeptical of that being the case. The problem is consistent with the engine hot or cold. And it starts at a touch of the key hot or cold and has a smooth idle. I wouldn't expect any such behavior with a cracked manifold. But to be open to all options, what's an easy way to diagnose?
1978 Eleganza II
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| Re: [GMCnet] Quadrajet problems [message #137726 is a reply to message #137721] |
Sat, 06 August 2011 08:50 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Ken, wildly fluctuating, and low, less than 18" of vacuum at idle, at the
manifold port, not carb. Vacuum gages are inexpensive, if you have one of
those mityvac suction tools, that gage will do fine. Visual check will be to
remove the carb, and look down the throat with a good light source. They are
easy to see.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sat, Aug 6, 2011 at 3:58 AM, Ken Harland <kwharland@bellsouth.net> wrote:
>
>
> James Hupy wrote on Sat, 06 August 2011 04:58
> > Ken, two things come readily to my mind. All the changes to the fuel
> system,
> > and no change in symptoms would indicate to me that the problem might not
> be
> > fuel related. I would take the cap off the distributor and check the
> advance
> > weights. I suspect that they are rusted solid, and you are not getting
> any
> > centrifigal advance. Two other possibilities might be split vacuum hoses,
> or
> > the worst case scenario, a cracked intake manifold. Hope this helps.
> > Jim Hupy
> I'm right with you on looking for other sources of the problem. I did
> check the mechanical advance and it's all working smoothly, even had
> evidence of fresh lube.
>
> I disconnected and blocked off vacuum hoses that are below the butterflies
> thinking the same as you...no change.
>
> I did not consider a cracked manifold (and hate to mind you!) but I suppose
> I have to consider all possibilities. I've read of others having that
> problem but don't remember the symptoms. But honestly, I'm skeptical of
> that being the case. The problem is consistent with the engine hot or cold.
> And it starts at a touch of the key hot or cold and has a smooth idle. I
> wouldn't expect any such behavior with a cracked manifold. But to be open
> to all options, what's an easy way to diagnose?
>
> --
> 1978 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Quadrajet problems [message #137727 is a reply to message #137726] |
Sat, 06 August 2011 09:03 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Yeah, I thought you were going to say a rough idle would be a dead giveaway...fortunately it's rock steady @ 18-19 inches. And there's no flaws visible under the carb either.
1978 Eleganza II
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| Re: Quadrajet problems [message #137733 is a reply to message #137646] |
Sat, 06 August 2011 09:49 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
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you can check for vacuum leaks around the carb gaskets by using a propane torch (unlit). propane will be sucked in through any loose fitting gasket and the idle speed will increase.
good luck,
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: Quadrajet problems [message #137737 is a reply to message #137733] |
Sat, 06 August 2011 10:05 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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| fred v wrote on Sat, 06 August 2011 10:49 |
you can check for vacuum leaks around the carb gaskets by using a propane torch (unlit). propane will be sucked in through any loose fitting gasket and the idle speed will increase.
good luck,
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Fred: same thing with wd-40.
C. Boyd
76 Crestmont
East Tennessee
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| Re: Quadrajet problems [message #137739 is a reply to message #137646] |
Sat, 06 August 2011 10:20 |
PettyVTX
Messages: 363
Registered: April 2011
Location: Winder Ga.
Karma: 1
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If you have headers check to see if a couple of plug wires burnt. I had this happen to me in a car when i was a kid rebuilt the carb several times changed distributor never thought about the wires it ran too good idleing was about to go in and see if it had jumped time and happened to move a wire while my friend was trying to reving it up and found my problem 3 wires burnt on the inside enough to conduct while idle but under a load they broke down. Man after that i started looking at the easy stuff first. Just someting else to look at.
Ted
Ex Avion now looking for a 23'
Jeep Wrangler Towd
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| Re: Quadrajet problems [message #137743 is a reply to message #137646] |
Sat, 06 August 2011 10:30 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
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Heres what you do if you want to know if its to lean or to rich. Start it and let it warm up. Leave it runnin or shut it off. Drive the pivot pin to the accelerator pump out and remove the arm. You now have no acc. pump. Drive it. If the problem is still there and/or worse,,,,,Its too lean. If it gets better,,,,,then it was to rich. Find out why. Stuck float??? Float too high. gas coming out through the senconary meetering holes because the flaps are letting air by. Did you remove the butterflys during the rebuild??? Again,,,I recomend you purchase and read TWICE Cliff Ruggles qjet book. JWID,,,,,,PL
Paul Leavitt
78 RB Royale
Galvanized frame,hubler front
500 Caddy and no dash,,,,,yet!!
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| Re: Quadrajet problems [message #137751 is a reply to message #137743] |
Sat, 06 August 2011 12:28 |
klassic kampers
Messages: 93
Registered: July 2008
Location: greer,s.c./ellijay,ga
Karma: 0
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not knowing the condition of your short block but a retarded camshaft(jumped timing gears/chain) display the same symtoms..this should not be your problem as if the gmc was running fine before parked it should be fine now.....make a reference mark on your distributor shaft and intake, rotate the distributor counterclockwise about 1/2 inch(or less) and see if the engine revs....the increased advance will improve throttle response if the cam or ignition timing were retarded............
the q-jets get warped as jim hupy states, but also from someone tightening down the long front 5/16" bolts too tight...I have seen the carb tops warped so badly that fuel cannot be transfered fron the main carb body to the nozzles.......these bolts should be just tight enough to crush a fresh lockwasher...
try to drive the gmc with the air cleaner and hatch cover removed(have fire extinguisher) and begin closing the choke flap...if the gmc picks up then there is still a carb problem of super lean.......be sure you can flow fuel from the main jets through the main wells and then to the emulsion tube housings.....old ethanol fuel likes to camp out in the bottom of the main wells and corrode that area............
before purchasing an expensive replacement carb, I would suggest getting a known good q-jet off of anything with 4 wheels, bolting on the gmc and testing.......hand throttle if needed........
Mike Stewart
1973 GMC 26' Canyonlands /
1973 B.S.A. B50 street tracker-----
Greer,S.C/Ellijay,Ga
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| Re: Quadrajet problems [message #137755 is a reply to message #137646] |
Sat, 06 August 2011 12:51 |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma: 0
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Senior Member |
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Thanks for all the good suggestions. Too many in answer individually but most all have been ruled out. Overall carb is in good shape, as I said ran fine before being parked for too long.
It's definitely too lean as I can bring it up in RPM to where it starts stumbling and manually close the choke slightly and it picks up RPM.
Right now I'm focused on the timing and/or the possibility of excessive exhaust back pressure. I'll look up timing specs as soon as I finish this post but presently it's at 16* initial with a total of 30-32 degrees with mechanical and vacuum combined. That seems a bit low to me but I'll know more shortly.
Vacuum readings do not seem to indicate exhaust blockage but that's the one thing that could certainly have developed while sitting, especially in Florida. I'm going to soak the manifold to header pipe bolts in penetrating lubricant and let sit for awhile.
1978 Eleganza II
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