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| [GMCnet] CARBS [message #106999] |
Sun, 28 November 2010 22:46  |
larry erd
Messages: 132
Registered: August 2010
Karma: 0
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Senior Member |
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I think the carb (Q jet) that came with my coach is not the original. I can
not find any model # on it at all, it looks like a rebuild, it's painted
black.I am assuming
a PO got a rebuilt at a parts store. The coach is all apart yet,but i need
to find out,IS THERE A NEW
MODERN CARB that will work on my 403 that is better or as good as the old Q
jets??
Larry Erd
77 Kingsley
lake Wales fl.
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| Re: [GMCnet] CARBS [message #107021 is a reply to message #106999] |
Mon, 29 November 2010 07:43  |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| larry erd wrote on Sun, 28 November 2010 20:46 |
... IS THERE A NEW
MODERN CARB that will work on my 403 that is better or as good as the old Q
jets??
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The PO of my '78 (w/403) installed an Edelbrock Performer #1903. Other items on the box: 795 M4MC Hot Air Choke, Fits 1975-1985 Chevy 305 thru 454 cid.
Just did a web search and unfortunately it seems to be "No Longer Available." <http://www.carburetion.com/Rochester.asp> 3rd carb down.
I do not know if he did any changes when installing it. The coach runs well and gets the expected gas mileage.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] CARBS [message #107023 is a reply to message #107021] |
Mon, 29 November 2010 08:40 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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Senior Member |
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| mike miller wrote on Mon, 29 November 2010 07:43 |
| larry erd wrote on Sun, 28 November 2010 20:46 |
... IS THERE A NEW
MODERN CARB that will work on my 403 that is better or as good as the old Q
jets??
|
The PO of my '78 (w/403) installed an Edelbrock Performer #1903. Other items on the box: 795 M4MC Hot Air Choke, Fits 1975-1985 Chevy 305 thru 454 cid.
Just did a web search and unfortunately it seems to be "No Longer Available." <http://www.carburetion.com/Rochester.asp> 3rd carb down.
I do not know if he did any changes when installing it. The coach runs well and gets the expected gas mileage.
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someone here has had good luck with a Holley carb. try searching the postings for it.
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: [GMCnet] CARBS [message #107082 is a reply to message #106999] |
Mon, 29 November 2010 20:26 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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Bryan said - "I was afraid to mention this here..."
Uh, oh - look out! An out-of-the box solution for a GMC? Heresy, I say. You might get drummed out of the corps.
Sorry I got snarky - no worries, it's great how people share their experiences here, even with a bit of trepidation. I know it's unpopular, but I bought some 16.5" tires last year, and nobody bloodied my lip. I even bought my coach site-unseen against the advice of this net, but landed in a pot of jam with a wonderful coach whose previous owner did some really marvelous upgrades. Folks here applauded, suggested, tried to one-up me, but it's a Palm Beach and that's hard to beat!
I had intended to go fuel injection in August or September, but the dog-gone carb is running so well since Jim K's guys tweaked it, and we had some unexpected expenses, so I drive her with the carb for a while. The crossovers are not yet plugged either and it runs beautifully - go figure.
Larry Davick
Fremont, California
The Mystery Machine
'76 (ish) Palm Beach
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] CARBS [message #107087 is a reply to message #106999] |
Mon, 29 November 2010 22:03 |
RadioActiveGMC
Messages: 1020
Registered: November 2010
Location: Hot AZ desert
Karma: 0
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Senior Member |
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I have the 455, but installed a Holly and it works great.
***"Gettin There"-1973 23' Sequoia-
Michael, Onans smell, "Go solar/wind power!"
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| Re: [GMCnet] CARBS [message #107107 is a reply to message #106999] |
Tue, 30 November 2010 06:13 |
petemosss
Messages: 221
Registered: August 2008
Location: Jacksonville, Florida
Karma: 0
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Mr. Radioactive, What kind of holley set up?
Duke chime in here and tell us again about your successful Holley Street Avenger rig.
Bryan, Mike Way to go trying something different.
I have a 51 and 57 numbered Q-Jet with one rebuilt with the correct goodies jet and rod wise so we'll see what happens.
Pete
74 Canyon Lands 26' "Emery"
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| Re: [GMCnet] CARBS [message #107136 is a reply to message #107023] |
Tue, 30 November 2010 10:09 |
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That someone would be I, its a Holley Street Avenger, you will need to get an adapter to mate it to the spread bore manifold unless you are running an aftermarket mani. Get the 670 CFM model 0-80670, it shoud be nearly dialed in out of the box, and depending on where you are you can drop it a jet size. also get the vac secondary spring tuner kit and accelerator camlobe kit, those can be had from jegs or summit for a few bucks. install the heaviest accelerator pump lobe, and heaviest vac spring for the secondaries, this will keep them from opening lower in the RPM band or while at cruise which will absolutely kill your milage. I clocked 10.5 mpg over almost 900 miles on a 455 with that setup, keeping cruise vacuum around 13-14 inches... I still have a little drag off idle sometimes which I think is an accelerator pump nozzle issue, ive just been too lazy to tune that out, since mashing the gass a little more cures it, but as soon as I do I will note which part will make the perfect Holley GMC carb...
| fred v wrote on Mon, 29 November 2010 08:40 |
| mike miller wrote on Mon, 29 November 2010 07:43 |
| larry erd wrote on Sun, 28 November 2010 20:46 |
... IS THERE A NEW
MODERN CARB that will work on my 403 that is better or as good as the old Q
jets??
|
The PO of my '78 (w/403) installed an Edelbrock Performer #1903. Other items on the box: 795 M4MC Hot Air Choke, Fits 1975-1985 Chevy 305 thru 454 cid.
Just did a web search and unfortunately it seems to be "No Longer Available." <http://www.carburetion.com/Rochester.asp> 3rd carb down.
I do not know if he did any changes when installing it. The coach runs well and gets the expected gas mileage.
|
someone here has had good luck with a Holley carb. try searching the postings for it.
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: [GMCnet] CARBS [message #107143 is a reply to message #107136] |
Tue, 30 November 2010 12:41 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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While I have no intension of replacing my quadrojet with a holly I was thinking you would need to also change the power valve on the holly to a 6.5 or less to keep it out of the fuel enrichment circuit as much as possible to get the better fuel mileage.That is unless it came with the lesser numbered power valve. I'm not sure I would want to use an even bore carburetor on a spread bore manifold. Doesn't the adapter cause the carburetor to be too close to the floor? I have mixed and matched carburetors on my hot rods many times with good luck . I prefer the Carter AFB over the holly for an even bore carburetor as they never seem to need any help but a lot of folks like the holly. As you point out in most cases smaller cfm is better unless the gas is cheap.
Roy
[quote title=Duce Apocalypse wrote on Tue, 30 November 2010 08:09]That someone would be I, its a Holley Street Avenger, you will need to get an adapter to mate it to the spread bore manifold unless you are running an aftermarket Mani. Get the 670 CFM model 0-80670, it shoud be nearly dialed in out of the box, and depending on where you are you can drop it a jet size. also get the vac secondary spring tuner kit and accelerator camlobe kit, those can be had from jegs or summit for a few bucks. install the heaviest accelerator pump lobe, and heaviest vac spring for the secondaries, this will keep them from opening lower in the RPM band or while at cruise which will absolutely kill your milage. I clocked 10.5 mpg over almost 900 miles on a 455 with that setup, keeping cruise vacuum around 13-14 inches... I still have a little drag off idle sometimes which I think is an accelerator pump nozzle issue, ive just been too lazy to tune that out, since mashing the gass a little more cures it, but as soon as I do I will note which part will make the perfect Holley GMC carb...
[A
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] CARBS [message #107290 is a reply to message #107143] |
Wed, 01 December 2010 21:35 |
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I'm actually running a barry grant 4 door power valve that opens at 7.5 vac, usually only sees that if I mash the pedal, though the stock 6.5 PV was probably enough. the spacer does require that you raise the hatch an inch, I did this for about a buck with a 1x2 from home depot. The 670 CFM is perfect for the 455 and is almost same as stock. out of the box the carb runs petty good. and wit ha little tweaking it made my bogged down motorhome run like it had a new engine in it. the old q-jet I think is really messed up inside.
[quote title=roy1 wrote on Tue, 30 November 2010 12:41]
While I have no intension of replacing my quadrojet with a holly I was thinking you would need to also change the power valve on the holly to a 6.5 or less to keep it out of the fuel enrichment circuit as much as possible to get the better fuel mileage.That is unless it came with the lesser numbered power valve. I'm not sure I would want to use an even bore carburetor on a spread bore manifold. Doesn't the adapter cause the carburetor to be too close to the floor? I have mixed and matched carburetors on my hot rods many times with good luck . I prefer the Carter AFB over the holly for an even bore carburetor as they never seem to need any help but a lot of folks like the holly. As you point out in most cases smaller cfm is better unless the gas is cheap.
Roy
| Duce Apocalypse wrote on Tue, 30 November 2010 08:09 |
That someone would be I, its a Holley Street Avenger, you will need to get an adapter to mate it to the spread bore manifold unless you are running an aftermarket Mani. Get the 670 CFM model 0-80670, it shoud be nearly dialed in out of the box, and depending on where you are you can drop it a jet size. also get the vac secondary spring tuner kit and accelerator camlobe kit, those can be had from jegs or summit for a few bucks. install the heaviest accelerator pump lobe, and heaviest vac spring for the secondaries, this will keep them from opening lower in the RPM band or while at cruise which will absolutely kill your milage. I clocked 10.5 mpg over almost 900 miles on a 455 with that setup, keeping cruise vacuum around 13-14 inches... I still have a little drag off idle sometimes which I think is an accelerator pump nozzle issue, ive just been too lazy to tune that out, since mashing the gass a little more cures it, but as soon as I do I will note which part will make the perfect Holley GMC carb...
[A
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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