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| [GMCnet] toop much money fopr my own good [message #74600] |
Sun, 21 February 2010 19:35  |
paul h cashman
Messages: 176
Registered: May 2005
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I have read here on the gmcnet,that you have to have an Original
Carburetor for your GMC.?
I had a Holly Carburetor on mine ,I could go off at a Traffic Light and
leave Cars behind me ,but the back two barrels wouldn't open.I thought ,I
checked everything,.
I went on the Internet and bought the Right Carburetor($250.00)r, sent it to
Dick Paterson to be rebuilt about (300.00) and guess what ?.I cant leave
Cars at a Red Light and the back two Barrels still not opening..
At the Dothan Rally .I talked with a fellow Dixie Landers from Lake Lanier
GA And he went on the top of his Gmc and brought me a Carburetor. I told
him mine was not like his. I had a Vacuum brake on the front..
I told him I removed the Vacuum brake and plugged it.He told me that was not
a good Idea..
To get the Vacuum brake to work your Vacuum has to be below 5 inches..my
Vacuum never drops below 7 inches at full Throttle. My Engine has 55,000
showing..I plugged the Vacuum and the back two barrels open now.
I should have spent the Money on WHORES AND BOOZE ..I would have at least
good /bad memories.
Paul Cashman
Riverdale Ga
89 Harley
78 GMC
78 Bug Convertible
75 Sting Ray
98 Lumina
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Paul H Cashman
Riverdale Ga
1978 Transmode
1975 Corvette
1978 Beetle Convertible
1989 Harley Davidson Sportster
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| Re: [GMCnet] toop much money fopr my own good [message #74613 is a reply to message #74600] |
Sun, 21 February 2010 20:47  |
Chr$
Messages: 2690
Registered: January 2004
Location: Scottsdale, AZ
Karma: 1
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Yeah, I shocked a woman in a new Tahoe this week when I took off from a light. Seems she was wanting in my lane and was going to take off from the light and get in front of the "old motorhome." When I heard her throttle go WOT, I did too. Good thing I did. She got behind me (reluctantly) then hit the brakes and turn right at the next street.
Some people have their head so far up their ass that they should be shot on site. She would most likely have gotten a GMC Motorhome up her ass instead if she had gotten in front of me as planned and I had taken it easy off that light. Sometimes having a lead foot pays off. I had someone jump in front of me at a red light while I was in a loaded U-haul before. What do these people think, that a loaded truck can stop like a new car?
I'm liking my new Tranny and Final Drive. Need to get that old carb off to rebuild.
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.
Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"
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| Re: [GMCnet] toop much money fopr my own good [message #74619 is a reply to message #74600] |
Sun, 21 February 2010 21:21 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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It sounds to me like the gas pedal needs to be adjusted because the front barrels are probably not opening all the way.
With the engine NOT running, remove the air cleaner and look down the carb at the FRONT barrels. Now press the gas petal all the way to the floor. Do the front butterflys in the barrels open all the way? Also with the petal all the way to the floor, grab the carb linkage and see if you can move the carb further open.
I have seen many GMC gas pedals the have been bent down over time. All you have to do to adjust it is to pull upon the pedal bending it slightly up until stepping on it opens the fronts all the way. Bending this also affects the adjustment of the passing gear switch which is mounted directly above the gas pedal.
Does your passing gear kick down work?
You could also have a stretched throttle cable.
Ken B
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] toop much money fopr my own good [message #75101 is a reply to message #74619] |
Sat, 27 February 2010 17:50 |
paul h cashman
Messages: 176
Registered: May 2005
Karma: 0
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Hi Ken,
With the Engine off and choke off , the back two Barrels open with W.O.T.
With the Engine running and Choke off at W.O.T. the back two barrels do not open , the Vacummn Brake on the Carburator is keeping them from opening.
I checked the Vacuum Brake, it doesnt drop off ,till about 4 inches of Vacumn .
With W.O.T. my Vacumn doesnt drop below 7 inches of Vacumn
so the back barrels cant open.
....................................Paul
Paul H Cashman
Riverdale Ga
1978 Transmode
1975 Corvette
1978 Beetle Convertible
1989 Harley Davidson Sportster
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| Re: [GMCnet] toop much money fopr my own good [message #75112 is a reply to message #75101] |
Sat, 27 February 2010 20:27 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Paul,
Please go back one posting and read it again. I was asking about the FRONT barrels opening all of the way. If the front barrels do not open completely you will have a higher vacuum level which will prevent the rears from opening. In my posting I was attempting to find why your vacuum does not drop below 7". I still think the front barrels are not opening all the way.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] toop much money fopr my own good [message #75126 is a reply to message #75118] |
Sun, 28 February 2010 00:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Dan,
I think we are getting lost here. I believe the quadrajet will not open the rear barrels unless the vacuum is below a certain level and the throttle is pressed nearly all the way open. He states that the lowest he can get the vacuum to go is 7". This sounds to me like he is not opening the throttle all the way even though he is pressing the petal all the way to the floor. I just think the gas petal is bent slightly preventing it from pulling all the way on the cable. I have straightened may of these on GMC's for people that complain about no passing gear. It is a common occurrence.
I'm trying in my mind to think if a badly clogged air cleaner or that heat riser valve in the air cleaner could cause the same failure. It might but the throttle linkage is the first thing I would look at since is it so common on the GMC.
I do not think anyone wants the vacuum to only go to 7" on their GMC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] toop much money fopr my own good [message #75132 is a reply to message #75129] |
Sun, 28 February 2010 07:26 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| Steven Ferguson wrote on Sun, 28 February 2010 06:52 |
Ken,
Clarification here: Is it the upper air doors that are not opening
or the lower throttle valves?
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I realize that. The upper butterfly (or door) is vacuum controlled. The bottom ones are part of the accelerator linkage. Both need to be open to get the air flow into the rear. He has found the problem with 7" of vacuum at full throttle. Once he fixes that then rear upper doors should open and he will have unrestricted air flow.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] toop much money fopr my own good [message #75136 is a reply to message #75132] |
Sun, 28 February 2010 08:24 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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| Ken Burton wrote on Sun, 28 February 2010 07:26 |
| Steven Ferguson wrote on Sun, 28 February 2010 06:52 |
Ken,
Clarification here: Is it the upper air doors that are not opening
or the lower throttle valves?
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I realize that. The upper butterfly (or door) is vacuum controlled. The bottom ones are part of the accelerator linkage. Both need to be open to get the air flow into the rear. He has found the problem with 7" of vacuum at full throttle. Once he fixes that then rear upper doors should open and he will have unrestricted air flow.
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Paul,
If you are only getting 7" of vacuum at what you say is WOT, you are NOT opening the throttle all of the way. As suggested by others, likely there is something wrong in the throttle linkage that is keeping it from opening. At a true WOT...primaries only...with secondaries locked out, your vacuum should be around 2"or less (unless you are at upper elevations...like say Denver where WOT vacuum will go to 0 very quickly)
It should be noted that the upper door is controlled by vacuum only in the sense that when the secondaries (large throttle valves) open, it creates a vacuum between the secondary throttle plates and the upper door. The positive pressure above the upper door pushes the upper door open, and in turn lifts the secondary rods allowing more fuel to enter the air flowing in. As the engine picks up speed under high power demand, more air flows through and that door opens more, lifting the secondary rods higher, allowing more fuel in. And so it goes until the motor goes to 4000 or more RPM the doors finally open all of the way. It is unlikely that given the low RPM's that we operate at, that those door will ever be fully open...even climbing the grape vine at WOT. If that door is not coming open, there is a mechanism (can't recall what it is termed and don't have the manual with me) that is designed to hold the upper door closed during warm-up when the choke is still on. If it is misadjusted or stuck, it could hold the door closed at all times, not allowing proper secondary operation. It is there to keep people from going WOT before the engine is warmed up. This thingy is located on the drivers side secondary barrel between the primary and secondary and is not necessary for good operation. I took mine off as I know better than to go WOT before the motor gets to full operating temp. Push down on the rear of the upper door with the engine cold. You will see what is holding it. No need to adjust that part, just remove it. In the mean time, make sure that your throttle linkage is working properly...opening the secondaries to full open when the throttle pedal is on the floor. JMHO
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: [GMCnet] toop much money fopr my own good [message #75140 is a reply to message #75136] |
Sun, 28 February 2010 08:51 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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I don't thing that is it in this case Larry as no matter what, there
is still only 7" of vacuum. Here is a photo of the "shoe" that can,
and frequently does, prevent the rear air doors from opening:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=17726&cat=3146
I think you are right, if the front throttle valves were able to open
all the way, vacuum would have to drop to nearly zero. It's probably
in the linkage.
On Sun, Feb 28, 2010 at 6:24 AM, Larry <weidnerl@wwt.net> wrote:
>
>
> Ken Burton wrote on Sun, 28 February 2010 07:26
>> Steven Ferguson wrote on Sun, 28 February 2010 06:52
>> > Ken,
>> > Clarification here: Is it the upper air doors that are not opening
>> > or the lower throttle valves?
>>
>> I realize that. The upper butterfly (or door) is vacuum controlled. The bottom ones are part of the accelerator linkage. Both need to be open to get the air flow into the rear. He has found the problem with 7" of vacuum at full throttle. Once he fixes that then rear upper doors should open and he will have unrestricted air flow.
>
> Paul,
>
> If you are only getting 7" of vacuum at what you say is WOT, you are NOT opening the throttle all of the way. As suggested by others, likely there is something wrong in the throttle linkage that is keeping it from opening. At a true WOT...primaries only...with secondaries locked out, your vacuum should be around 2"or less (unless you are at upper elevations...like say Denver where WOT vacuum will go to 0 very quickly)
>
> It should be noted that the upper door is controlled by vacuum only in the sense that when the secondaries (large throttle valves) open, it creates a vacuum between the secondary throttle plates and the upper door. The positive pressure above the upper door pushes the upper door open, and in turn lifts the secondary rods allowing more fuel to enter the air flowing in. As the engine picks up speed under high power demand, more air flows through and that door opens more, lifting the secondary rods higher, allowing more fuel in. And so it goes until the motor goes to 4000 or more RPM the doors finally open all of the way. It is unlikely that given the low RPM's that we operate at, that those door will ever be fully open...even climbing the grape vine at WOT. If that door is not coming open, there is a mechanism (can't recall what it is termed and don't have the manual with me) that is designed to hold the upper door closed during warm-up when the choke is still on. If it is mis
> adjusted or stuck, it could hold the door closed at all times, not allowing proper secondary operation. It is there to keep people from going WOT before the engine is warmed up. This thingy is located on the drivers side secondary barrel between the primary and secondary and is not necessary for good operation. I took mine off as I know better than to go WOT before the motor gets to full operating temp. Push down on the rear of the upper door with the engine cold. You will see what is holding it. No need to adjust that part, just remove it. In the mean time, make sure that your throttle linkage is working properly...opening the secondaries to full open when the throttle pedal is on the floor. JMHO
> --
> Larry :)
> 78 Royale w/500 Caddy
> Menomonie, WI.
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--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: [GMCnet] toop much money fopr my own good [message #75151 is a reply to message #74600] |
Sun, 28 February 2010 10:19 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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As others mentioned but in some sort of order:
1) make sure you have WOT 90 on both primary and secondary throttle plates. Best done with a real live foot (assistant req) while you look down the Qjet with the Choke held open and the secondary air valve held open. You need two hands free and a flashlight. The primaries should rotate about 45 deg or so and then in the last 45 deg rotate the secondaries their full 90. It's sort of a compounding linkage. The length of the LH rod is bend to adjust to spec.
2)Make sure the secondary vac break is holding vac and moving freely. (suck on a test piece of vac hose on the break) there is a specifc orifice size tuned to the application that is the time constant for deployment of the the diaphragm. Could be dirt in there or someone "drilled it out" or the wrong one is installed. Age kills these things too.
3) Make sure the choke is opening the secondary air valve lock out during the last few degrees of rotation of the choke to OFF. (This requires the choke to first be working and have a heat signal and not be gummed up and adjusted correctly including the unloader adjustment.) Or remove it. Nahhh. Why not just adjust it proprly? It's there to prevent you from bogging and stalling a cold engine and like blocking an intersction or worse a freight train. That tiny little part could save lives under just the right conditions. GM put it there for a reason. You might never ever need it. Then again when you need it you REALLY need it.
4) Adjust the length of the the vac break actuator rod to spec to the secondary air valve. Again these mesurements are posted somewhere so there is the correct amount of slack. Make sure the secondary air valve rotates freeling all the way and is lifting the rod hanger properly. If the plates are sticking on the top air horn you loosten the slot screws to recenter the plates.
5)IMPORTANT Adjust the secondary air valve spring pre-load to spec. You have to loosen the allen on the sec air valve adjust screw and then adj the screw wind up (small straight blade) to set the wind up tension and then tighten the allen to hold the adj. This is the "tuning" part of the process and takes a few runs to get it right. You want the engine at full warm up and then you adjust (loosten) the tension so it just doesn't bog. Too tight and the air valve won't open soon enough or all the way (lack perf) and too loose you will get hessitation bog during the transition.
If all this is correct you should have a working set of secondaries on your Qjet and associated noise. (or 455 music if you prefer)
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] toop much money fopr my own good [message #75170 is a reply to message #74600] |
Sun, 28 February 2010 13:41 |
Ernest Dankert
Messages: 133
Registered: May 2007
Location: Ogden, New York
Karma: 1
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Before monkeying with the carb, and for sure trouble shooting the secondaries, make sure the timing is right where you want it to be. Case in point, I could not get my secondaries to open when the timing was 15 degrees retarded from spec. Next make sure the mufflers are not obstructed, you need to pass gas to make vacuum. Vacuum will open the secondaries.
There will be a point at low vacuum where the secondaries will close and just primaries will be open. More pronounced when lugging and losing rpm's in climbing a hill.
All my life I spent money on women, whiskey and gambling, the rest I just wasted.
1977 Eleganza II
Ogden NY
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| Re: [GMCnet] toop much money fopr my own good [message #75216 is a reply to message #75112] |
Sun, 28 February 2010 19:06 |
paul h cashman
Messages: 176
Registered: May 2005
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Senior Member |
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Ken,That is the only thing that makes sense.
I'm sure they are opening all the way,but I will check again. I've looked down the barrels many times
This Carburator was rebuilt by Dick Patterson.
The Original Holly Carb, did the same thing ,the back two barrels wouldnt open.
The Vacuum Brake energizes at 3 to 4 inches Hg.and lower to drop out.
I check the Vacuum on a hill at W.O.T.several times
Paul H Cashman
Riverdale Ga
1978 Transmode
1975 Corvette
1978 Beetle Convertible
1989 Harley Davidson Sportster
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| Re: [GMCnet] toop much money fopr my own good [message #75239 is a reply to message #75216] |
Sun, 28 February 2010 22:46 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Here is another way you can check if the gas pedal rod is bent down. Look under the dash for the transmission kick down switch. It is located on the upper end of the gas pedal rod. Press the pedal all the way to the floor and watch the switch. It should move the switch all the way. If it does not then the rod is bent. Pull up on the rod bending it slightly until the switch moves to it's limit when the pedal is pressed all the way to the floor. This only takes a minute and requires no tools.
I have never seen a stretched throttle cable but I did see somewhere a suggestion to add a fishing sinker on the cable to make up for the stretch. I still think you have a slightly bent gas pedal rod.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] toop much money fopr my own good [message #75246 is a reply to message #75239] |
Sun, 28 February 2010 23:27 |
amansfield1104
Messages: 80
Registered: August 2009
Karma: 0
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I had several problems with mine when I first got it. They stated with the spring on the throttle return. The one who owned before me put a very stiff sponge at the carb end and starched the cable. I could only get about half throttle. It took me a while to get this figured out. Then when I got springs fixed and the cable adjusted. My secondaries would not operate. The rod between the choke and the secondary vacuum butterfly would not allow the butterfly to open. I bent it until it would allow it to open then the secondary worked. Do they work as design, I have no idea. I know that mine still has poor acceleration.
Art Mansfield
76 ELII
Decatur Al
On Feb 28, 2010, at 10:46 PM, Ken Burton wrote:
>
>
> Here is another way you can check if the gas pedal rod is bent down. Look under the dash for the transmission kick down switch. It is located on the upper end of the gas pedal rod. Press the pedal all the way to the floor and watch the switch. It should move the switch all the way. If it does not then the rod is bent. Pull up on the rod bending it slightly until the switch moves to it's limit when the pedal is pressed all the way to the floor. This only takes a minute and requires no tools.
>
> I have never seen a stretched throttle cable but I did see somewhere a suggestion to add a fishing sinker on the cable to make up for the stretch. I still think you have a slightly bent gas pedal rod.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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