Home » Public Forums » GMCnet » Assessing coach - carb issues
| Assessing coach - carb issues [message #216167] |
Mon, 29 July 2013 19:50  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Hi folks,
On my first road trip and seem to have some carb issues. Took it all the way down, cleaned it and put it back together. The driver side primary I can still see gas dripping (under the choke plate from the little piece protruding into the center of the barrel), and the passenger side I cannot. What passage would I have missed for that to not be atomizing? Other issues I need to look for if I break down the carb again?
Thanks,
Tyler
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing coach - carb issues [message #216774 is a reply to message #216167] |
Sat, 03 August 2013 11:18  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Still out on first trip, still getting 4.8 mpg -
I've taken carb apart twice - here is the only difference I can see
https://dl.dropboxusercontent.com/u/2984589/DSCN5865.JPG
There are five holes to the inside/above/beside each venturi. Two of the five have brass inserts on the accelerator pump side and only one has a brass insert on the right (passenger) side. Did someone rip out a brass fitting on a previous rebuild/clean?
Bonus question: This is a picture of the bottom plate. there is a little tab dead center between what I think are vacuum ports below the smaller, primary butterflies.
https://dl.dropboxusercontent.com/u/2984589/DSCN5866.JPG
The primary metering (terminology?) pins hang on a brass cylinder that comes through and apparently bottoms on this little tab. Is this tab supposed to move, or is mine gunked in place?
TIA
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing coach - carb issues [message #216794 is a reply to message #216774] |
Sat, 03 August 2013 13:42 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| Tilerpep wrote on Sat, 03 August 2013 09:18 |
Still out on first trip, still getting 4.8 mpg -
I've taken carb apart twice - here is the only difference I can see
https://dl.dropboxusercontent.com/u/2984589/DSCN5865.JPG
There are five holes to the inside/above/beside each venturi. Two of the five have brass inserts on the accelerator pump side and only one has a brass insert on the right (passenger) side. Did someone rip out a brass fitting on a previous rebuild/clean?
Bonus question: This is a picture of the bottom plate. there is a little tab dead center between what I think are vacuum ports below the smaller, primary butterflies.
https://dl.dropboxusercontent.com/u/2984589/DSCN5866.JPG
The primary metering (terminology?) pins hang on a brass cylinder that comes through and apparently bottoms on this little tab. Is this tab supposed to move, or is mine gunked in place?
TIA
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From what I can see in the photos, there does not appear to be any main jets in the holes for them. Maybe you took them out for cleaning and took the pic then, but if they are missing, the fuel is not being metered properly and you are running very rich on the high speed circuit.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
[Updated on: Sat, 03 August 2013 13:44] Report message to a moderator |
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| Re: Assessing coach - carb issues [message #216803 is a reply to message #216167] |
Sat, 03 August 2013 15:39 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Carl, the main jets are out on purpose in cleaning solution- the very small pressed in brass fittings are what don't seem to match. The holes are right next to the threaded holes that receive the flat head screws below the main throttle plate when fully assembled.
Matt, I'm afraid if they are pressed in, a breakdown guide won't show them. I'll need to look for that manual when not on phone.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing coach - carb issues [message #216805 is a reply to message #216803] |
Sat, 03 August 2013 15:50 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| Tilerpep wrote on Sat, 03 August 2013 13:39 |
Carl, the main jets are out on purpose in cleaning solution- the very small pressed in brass fittings are what don't seem to match. The holes are right next to the threaded holes that receive the flat head screws below the main throttle plate when fully assembled.
Matt, I'm afraid if they are pressed in, a breakdown guide won't show them. I'll need to look for that manual when not on phone.
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Okay, I was hoping that was the case and that someone had taken them out and left them out. I don't think it would even run without the mains. Maybe...but really rich.
Sorry, I don't know enough about the Q-jet to know how critical that other brass part that's missing is, but it might be contributing to the bad mileage.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Assessing coach - carb issues [message #216814 is a reply to message #216167] |
Sat, 03 August 2013 16:58 |
AStasunas
Messages: 58
Registered: April 2009
Location: Winter Springs, Fl
Karma: 0
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Hard to see in the photo, but it looks like the idle channel restrictiction is missing from the right side. Use some small number size drills and compare the right and left sides
"Vinnie"
1975 Eleganza,
Winter Springs, Fl
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| Re: Assessing coach - carb issues [message #216821 is a reply to message #216816] |
Sat, 03 August 2013 18:24 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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That's a term I have not seen yet, but sounds very likely. I can put an aerosol extension tube down the one without, and not the one with the brass fitting...so if logic dictates that they should be the same, what might be a fix, especially before I put it together to go home? (ha! extra challenge)
And for the adventurous who wonder "why" like me - why would the "unrestricted" one not leak/drip, and the one that looks like it has the restrictor be the one that drips? Does it draw more/unbalanced vacuum and thus pull more gas?
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: Assessing coach - carb issues [message #216888 is a reply to message #216167] |
Sun, 04 August 2013 14:29 |
AStasunas
Messages: 58
Registered: April 2009
Location: Winter Springs, Fl
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The only place to get one is another carb body to replace yours, or you could make one from a brass rod and drill the same size hole.
I don't understand the fluid dynamics involved, but Cliff Ruggles in his book suggests this changes the air flow though the Venturi.
I'd look on ebay for a carb body to match your carb number. Good luck.
"Vinnie"
1975 Eleganza,
Winter Springs, Fl
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| Re: [GMCnet] Assessing coach - carb issues [message #216901 is a reply to message #216888] |
Sun, 04 August 2013 16:22 |
powerjon
Messages: 2446
Registered: January 2004
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Or you could send it to Dick Patterson and you will get a carb back that is set up for your motor and will work correctly.
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
On Aug 4, 2013, at 3:29 PM, Anthony Stasunas <AStasunas@aol.com> wrote:
>
>
> The only place to get one is another carb body to replace yours, or you could make one from a brass rod and drill the same size hole.
> I don't understand the fluid dynamics involved, but Cliff Ruggles in his book suggests this changes the air flow though the Venturi.
>
> I'd look on ebay for a carb body to match your carb number. Good luck.
> --
> "Vinnie"
> 1975 Eleganza,
> Winter Springs, Fl
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Assessing coach - carb issues [message #216988 is a reply to message #216901] |
Mon, 05 August 2013 00:23 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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I would also check the Ignition system.
On Sun, Aug 4, 2013 at 2:22 PM, John Wright <powerjon@chartermi.net> wrote:
> Or you could send it to Dick Patterson and you will get a carb back that
> is set up for your motor and will work correctly.
>
> JR Wright
> 78 Buskirk Stretch
> 75 Avion
> Michigan
>
> On Aug 4, 2013, at 3:29 PM, Anthony Stasunas <AStasunas@aol.com> wrote:
>
> >
> >
> > The only place to get one is another carb body to replace yours, or you
> could make one from a brass rod and drill the same size hole.
> > I don't understand the fluid dynamics involved, but Cliff Ruggles in his
> book suggests this changes the air flow though the Venturi.
> >
> > I'd look on ebay for a carb body to match your carb number. Good luck.
> > --
> > "Vinnie"
> > 1975 Eleganza,
> > Winter Springs, Fl
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Assessing coach - carb issues [message #217066 is a reply to message #216988] |
Mon, 05 August 2013 14:08 |
Sammy Williams
Messages: 522
Registered: August 2010
Karma: -2
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A few words. Check ignition system and consider a rebuilt carb efi or an
edelbrock 1496. Sammy
On Aug 5, 2013 12:23 AM, "Jim Kanomata" <jimkanomata@gmail.com> wrote:
> I would also check the Ignition system.
>
>
>
> On Sun, Aug 4, 2013 at 2:22 PM, John Wright <powerjon@chartermi.net>
> wrote:
>
> > Or you could send it to Dick Patterson and you will get a carb back that
> > is set up for your motor and will work correctly.
> >
> > JR Wright
> > 78 Buskirk Stretch
> > 75 Avion
> > Michigan
> >
> > On Aug 4, 2013, at 3:29 PM, Anthony Stasunas <AStasunas@aol.com> wrote:
> >
> > >
> > >
> > > The only place to get one is another carb body to replace yours, or you
> > could make one from a brass rod and drill the same size hole.
> > > I don't understand the fluid dynamics involved, but Cliff Ruggles in
> his
> > book suggests this changes the air flow though the Venturi.
> > >
> > > I'd look on ebay for a carb body to match your carb number. Good luck.
> > > --
> > > "Vinnie"
> > > 1975 Eleganza,
> > > Winter Springs, Fl
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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