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| - secondary's not opening - more info [message #365534] |
Mon, 19 July 2021 12:10  |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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The coach starts easy and runs smooth, takes off nicely but when i put my foot in it very little happens-
I ran it with the cover off and watched the carb- secondary not opening. I poked around a bit and i understand it has something to with the choke being fully open.
And there's a vacuum diaphragm in front that does something?
If someone could explain what normal operation looks like i can probably form a more intelligent question.
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
[Updated on: Fri, 23 July 2021 16:44] Report message to a moderator |
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| Re: Next Noob Question- secondary's not opening [message #365538 is a reply to message #365534] |
Mon, 19 July 2021 15:56  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
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1. Some q-jets have a little tag on far passenger side of choke that blocks the secondary from opening. When choke is fully open that should push the tang in and allow the secondary to open. Try opening the secondary by pushing open with screwdriver. You should see how that works.
2. Secondarys open when vacuum is low. Basically a vacuum
Plunger holds them
Closed. As you hammer
The has vacuum drops and the plunger no longer has ability to hold them closed. Think opposite of how your cruise
Control
Works.
Having a vacuum gauge to diagnose is helpful. They rarely open in normal driving. You have to be smashing the throttle down. Just putzing normally you may not see them
Open.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Next Noob Question- secondary's not opening [message #365551 is a reply to message #365534] |
Mon, 19 July 2021 20:34 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If the choke is fully open, the lockout tab clear and they still don’t open try this test. Push down on the larger rear part with your finger and the air valves should not touch or scrape the air horn. If they do, just loosen the air valve screws about 3/4 turn and recenter the air valve plates on the shaft so they do not touch anything, then resnug the 2 screws on each. Do not loosen more than a turn or you risk dropping them into the carb and engine. The screws are thinner than the holes in plates to allow adjustment.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: - secondary's not opening - more info- NO POWER [message #365644 is a reply to message #365534] |
Fri, 23 July 2021 17:00 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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Ok, i figured out how it's supposed to work and everything seems to be doing what it's supposed to.
The choke opens completely, allowing everything else to open.
When i hit the throttle I see large amounts of fuel spraying into the intake, everything looks fine.
But on the road when I do that it bogs down and loses power.
Timing? i put a light on it but the timing mark is not visible. Lots of surface rust.
But i can tell with my timing light that it is advancing.
It have NEW HEI
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: - secondary's not opening - more info [message #365646 is a reply to message #365534] |
Fri, 23 July 2021 17:25 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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When you rev it in park the secondary air valve should only slightly open visually. If it is flopping wide open the front dash pot is bad, vac hose to it is bad or spring on air valve set too loose. The front dashpot has a less than pin hole orifice to hold back the opening time after the vacuum to the pot drops. It should open gradually in gear under load as you floor it. Fuel is heavy compared to air an takes time to match the more rapidly accelerating air. If air valve opens too soon you get bog. If the front dashpot and hose to it are good, you can increase spring wind up tension on the air valve. You hold the flat blade screw with a small driver, loosen the locking allen and slightly turn the screw for more tension, then tighten allen lock screw.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Fri, 23 July 2021 17:27] Report message to a moderator |
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| [GMCnet] Re: - secondary's not opening - more info [message #365647 is a reply to message #365646] |
Fri, 23 July 2021 18:01 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Also, if you "Stomp" the accelerator clean to the floor at too low of an
RPM, it will bog. Feed the throttle in gradually. If that works, then the
problem is not in the Carb, but in your foot. If it still bogs, then you
have a problem with too weak of a spring on the secondaries. There are
various springs for different applications on GM vehicles. Lastly, If you
are still running the 3:07 to 1 differential ratio, a solution might be to
go to a 3:55 or 3:70 to 1 final drive ratio.
Jim Hupy
Salem, Oregon
On Fri, Jul 23, 2021 at 3:26 PM John R. Lebetski
wrote:
> When you rev it in park the secondary air valve should only slightly open
> visually. If it is flopping wide open the front dash pot is bad, vac hose
> to it is bad or spring on air valve set too lose. The front dashpot has a
> less than pin hole orifice to hold back the opening time after the vacuum
> to the pot drops. It should open gradually in gear under load as you floor
> it. Fuel is heavy compared to air an takes time to match the more rapidly
> accelerating air. If air valve opens too soon you get bog. If the front
> dashpot and hose to it are good, you can increase spring wind up tension on
> the air valve. You hold the flat blade scrre with a small driver, loosen
> the locking allen and slightly turn the screw for more tension, then tighten
> allen lock screw.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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| Re: [GMCnet] Re: - secondary's not opening - more info [message #365666 is a reply to message #365647] |
Sun, 25 July 2021 06:43 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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James Hupy wrote on Fri, 23 July 2021 18:01Also, if you "Stomp" the accelerator clean to the floor at too low of an
RPM, it will bog. Feed the throttle in gradually. If that works, then the
problem is not in the Carb, but in your foot. If it still bogs, then you
have a problem with too weak of a spring on the secondaries.
I've taken a few test drives to articulate this problem.
From a dead stop it takes off very smoothly with a light touch on the throttle, if i leave my foot in the same spot it will very slowly accelerate to 45 mph or so, but if i give it any more gas it bogs no matter how gently i feather it.
This problem came on over a short period of time.
The coach had been completely gone over in 2013 with a new/rebuilt carb, distributor, wiring etc. It drove up here here to NC from the COOP and ran fine. Then it sat until 2020.
When i first took it on there was a lot of cranking and pouring gas down it's throat before it sparked. Then i got it running pretty good with fresh fuel.
At that point it behaved like the muscle car it is. When i stomped on the throttle it roared and launched like a 10,000 lb missile.
Then it started having a power loss under load. I changed several dirty fuel filters but that seemed to have little effect. It was getting harder to start and had less power.
Then it lost spark. I diagnosed the HEI, installed new components and it ran great, it starts instantly and idles smoothly but this power problem has not gone away.
So it appears the ignition problem masked or imitated an intermittant fuel problem but when i got the spark right the fuel problem is still there.
I think i've ruled out issues related to dirty fuel, clogged filter, bad pump, etc.
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| [GMCnet] Re: - secondary's not opening - more info [message #365673 is a reply to message #365666] |
Sun, 25 July 2021 17:20 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Is your distributor advance working properly?
Or is it frozen in place with corrosion?
D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com
________________________________
From: dave silva
Sent: Sunday, July 25, 2021 06:43
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Re: - secondary's not opening - more info
James Hupy wrote on Fri, 23 July 2021 18:01
> Also, if you "Stomp" the accelerator clean to the floor at too low of an
> RPM, it will bog. Feed the throttle in gradually. If that works, then the
> problem is not in the Carb, but in your foot. If it still bogs, then you
> have a problem with too weak of a spring on the secondaries.
I've taken a few test drives to articulate this problem.
From a dead stop it takes off very smoothly with a light touch on the throttle, if i leave my foot in the same spot it will very slowly accelerate to
45 mph or so, but if i give it any more gas it bogs no matter how gently i feather it.
This problem came on over a short period of time.
The coach had been completely gone over in 2013 with a new/rebuilt carb, distributor, wiring etc. It drove up here here to NC from the COOP and ran
fine. Then it sat until 2020.
When i first took it on there was a lot of cranking and pouring gas down it's throat before it sparked. Then i got it running pretty good with
fresh fuel.
At that point it behaved like the muscle car it is. When i stomped on the throttle it roared and launched like a 10,000 lb missile.
Then it started having a power loss under load. I changed several dirty fuel filters but that seemed to have little effect. It was getting harder to
start and had less power.
Then it lost spark. I diagnosed the HEI, installed new components and it ran great, it starts instantly and idles smoothly but this power problem has
not gone away.
So it appears the ignition problem masked or imitated an intermittant fuel problem but when i got the spark right the fuel problem is still there.
I think i've ruled out issues related to dirty fuel, clogged filter, bad pump, etc.
--
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| [GMCnet] Re: - secondary's not opening - more info [message #365674 is a reply to message #365673] |
Sun, 25 July 2021 17:32 |
Nelson
Messages: 120
Registered: August 2014
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Maybe check for blockage in the exhaust system .
Sent from my iPhone
Nelson Wright
Orlando Fl.
> On Jul 25, 2021, at 6:20 PM, D C _Mac_ Macdonald wrote:
>
> Is your distributor advance working properly?
> Or is it frozen in place with corrosion?
>
> D C "Mac" Macdonald
> Amateur Radio K2GKK
> Since 30 November '53
> USAF and FAA, Retired
> Member GMCMI & Classics
> Oklahoma City, OK
> "The Money Pit"
> TZE166V101966
> '76 ex-Palm Beach
> k2gkk + hotmail dot com
> ________________________________
> From: dave silva
> Sent: Sunday, July 25, 2021 06:43
> To: gmclist@list.gmcnet.org
> Subject: [GMCnet] Re: - secondary's not opening - more info
>
> James Hupy wrote on Fri, 23 July 2021 18:01
>> Also, if you "Stomp" the accelerator clean to the floor at too low of an
>> RPM, it will bog. Feed the throttle in gradually. If that works, then the
>> problem is not in the Carb, but in your foot. If it still bogs, then you
>> have a problem with too weak of a spring on the secondaries.
>
>
> I've taken a few test drives to articulate this problem.
>
> From a dead stop it takes off very smoothly with a light touch on the throttle, if i leave my foot in the same spot it will very slowly accelerate to
> 45 mph or so, but if i give it any more gas it bogs no matter how gently i feather it.
>
> This problem came on over a short period of time.
>
> The coach had been completely gone over in 2013 with a new/rebuilt carb, distributor, wiring etc. It drove up here here to NC from the COOP and ran
> fine. Then it sat until 2020.
>
> When i first took it on there was a lot of cranking and pouring gas down it's throat before it sparked. Then i got it running pretty good with
> fresh fuel.
>
> At that point it behaved like the muscle car it is. When i stomped on the throttle it roared and launched like a 10,000 lb missile.
>
> Then it started having a power loss under load. I changed several dirty fuel filters but that seemed to have little effect. It was getting harder to
> start and had less power.
>
> Then it lost spark. I diagnosed the HEI, installed new components and it ran great, it starts instantly and idles smoothly but this power problem has
> not gone away.
>
> So it appears the ignition problem masked or imitated an intermittant fuel problem but when i got the spark right the fuel problem is still there.
>
> I think i've ruled out issues related to dirty fuel, clogged filter, bad pump, etc.
>
>
>
>
>
>
>
> --
> Dave & Ellen Silva
> Hertford, NC
>
> 76 Birchaven, 1-ton and other stuff
>
> Currently planning the Great american Road Trip Summer 2021
>
> It's gonna take a lot of Adderall to get this thing right.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
_______________________________________________
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| Re: - secondary's not opening - more info [message #365677 is a reply to message #365534] |
Sun, 25 July 2021 20:44 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Recent experience(july)
Coach showed up in my neck of the woods. Guy revived a coach, fixed a few things(fuel filters, put cherry bomb mufflers on because old ones were blown, few other things including new batteries)
Took off from Pennsylvania and drove to mn. Had many other issues but ran strong and good power.
Then while here in MN for a week, he had power issues. Seemed like fuel. Replaced fuel filters again, and they were dirty already. Full tune up. No improvement.
He met up
With another super gmc guy and they swapped on a spare carb and that fixed it. He drove coach further west and back to Pennsylvania.
So from what your story is, i am leaning toward carb has some issues that are now shown up from bad gas.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
[Updated on: Sun, 25 July 2021 20:47] Report message to a moderator |
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| Re: - secondary's not opening - more info [message #365678 is a reply to message #365534] |
Sun, 25 July 2021 22:56 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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I think Jon is on to something.
Maybe it's a plugged fuel filter
after sitting for several months the
gas may be dirty.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: - secondary's not opening - more info [message #365679 is a reply to message #365678] |
Mon, 26 July 2021 09:00 |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
Karma: 0
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When you mention filters, you haven't specifically mentioned the one at the carb. A carb swap would likely get that when it was possibly the only problem.
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| Re: - secondary's not opening - more info [message #365680 is a reply to message #365534] |
Mon, 26 July 2021 09:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Need more info to solve. Is this issue happening in the first 1/3 of pedal travel (carb primaries only) or only when you push past that 1/3 pedal travel and open the secondaries. You should be able to feel the resistance of pushing against the secondary return spring so you know when you are starting to open the secondaries for reference.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: - secondary's not opening - more info [message #365684 is a reply to message #365680] |
Mon, 26 July 2021 12:23 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Senior Member |
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Yes, i have changed the main filter and the filter on the carb.
I recently opened the distibutor and swapped out the control board and the coil. timing advance looks good.
Also, when i rev it with a timing light on i can se it advance.
It is possible the timing is messed up.
On the first 1/3 of pedal travel it runs great and accelerates very slowly.
It bogs down when i try to go past that, no matter how gentle i am.
This problem have been slowly getting worse over the last 200 miles. (all short test drives)
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: - secondary's not opening - more info [message #365717 is a reply to message #365534] |
Tue, 27 July 2021 15:09 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
Karma: 0
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Senior Member |
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A very wise GMCer PM'd me suggesting it might be a cracked intake manifold.
That fits perfectly with the symptoms.
While the coach had a slew of problems related to sitting for a long time; each time i fixed one (fuel filter, bad gas, etc) I would get a slight improvement but overall the problem kept getting worse no matter what else got better.
This seems to line up perfectly with a crack that is growing with each heat cycle.
I have not had a chance to back and test for this (ether?)
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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