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quadrajet carb
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Supporting Member of Barthmobile.com 6/12
Formally known as "Humbojb"
Picture of Jim and Tere
posted
Ran into something recently that I thought might be helpful to others. My 85 Regal has a carburated 454 and while cruising back from Townsend, Tenn last week, we lost power from the engine. It didn't stop running, just wouldn't go anywhere. I nursed it home by flooring it on the flat and downhill and praying like mad that it would get up hill. Did all the normal things, replaced filters in the fuel lines, checked timing, plugs, wires, distributor cap etc. Each time, the test drive was the same wild ride trying to get back home. Then I remembered that the old Webers in my Volvo had a strainer in the carb. Guess what? So does the Quadrajet. Took off the fuel line and pulled out a paper filter. It didn't look too dirty but it's spring loaded and it was fairly easy to blow through it. I bought a new one which was very hard to blow through and we installed it and all is well. Don't really understand what happened, must have something to do with the little one way valve in the filter. It must have broken and the minute it did, the engine was starved for fuel. Anybody ever have a similar event?
Jim


Jim and TereJim and Tere

1985 Regal
29' Chevy 454 P32
8411 3172 29FP3B
Gear Vendor 6 Speed Tranny
 
Posts: 3308 | Location: madisonville tn usa | Member Since: 02-19-2005Reply With QuoteReport This Post
First Month Member
Supporting Member of Barthmobile.com 11/13
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That little filter, if properly installed, is not only a filter, but is also a pressure relief valve. That is, if the filter element is clogged, fuel pressure will push it into the spring and allow unfiltered fuel to enter the carb.

Unfortunately, crud can also get into the carb when that happens. That filter needs to be changed fairly often, and the threads in the carb need anti-seize or Lubriplate.


.

84 30T PeeThirty-Something, 502 powered
 
Posts: 7397 | Location: AZ Central Highlands | Member Since: 01-09-2001Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 6/12
Formally known as "Humbojb"
Picture of Jim and Tere
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Bill, I wonder if I installed it properly? One end had a hole in it that you could blow through and that was what we set up to be the inlet side of the filter. That end also had a little black rubber washer on it. The other end was solid. If the pressure relief valve wasn't working properly, what would the result be?
Also, I've heard of this carburator being called a "quadrajunk" carb. Is there a direct replacement that is better, or is this just sour grapes?
Thanks
Jim


Jim and TereJim and Tere

1985 Regal
29' Chevy 454 P32
8411 3172 29FP3B
Gear Vendor 6 Speed Tranny
 
Posts: 3308 | Location: madisonville tn usa | Member Since: 02-19-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/12
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Can't be installed backwards......
Been there - Tried that.....
 
Posts: 1407 | Location: Frederick, Maryland | Member Since: 09-12-2003Reply With QuoteReport This Post
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Supporting Member of Barthmobile.com 11/13
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quote:
Originally posted by humbojb:
I've heard of this carburetor being called a "quadrajunk" carb. Is there a direct replacement that is better, or is this just sour grapes?
Thanks
Jim


Jim, there are people who think in absolutes, and for some of them a carb that doesn't fit their needs perfectly is junk, and they adopt a partisan, even Chauvinist position. These are often guys who have used a Holley with good results on a hot rod or boat. Perhaps they have been humbled by a Qjet.

Like those guys, I have used a Holley with good results on hot rods and boats. In fact, I would not use a Qjet on anything but a stocker or an RV. On a stocker, the Qjet is good on gas and those small primaries give good mileage and off-idle throttle response. On a motor home, the Q jet has another advantage in that it does not have all those diaphragms and gaskets to suffer heat prostration and leak. Motor home fires are no fun. However there is a soft plug under the bottom of a Qjet that can leak and cause a fire, too. Look for stains

I think another reason some denigrate the Qjet is that it is time consuming to get the secondary windup and jets and needles just right. Heck, it is difficult just to get the top back on! I had really good carb shop do my Qjet. The Holley is easier to tune, but I don't use them on RVs or stockers.

Another maintenance item of a Qjet is that the nitrile float can absorb fuel and affect the float level.

There are happy Edelbrock carb RVers out there, but I have never used one. I had the best guys do my Qjet on a flow bench for the price of an untuned Edelbrock.

I had a Holley spread bore Qjet replacement, and it was not as good as a Qjet. 6619, I believe. Others had similar experience.

HP books sells a Rochester book by a GM engineer named Doug Roe. All his stuff is golden. Maybe Jake used to know him.


.

84 30T PeeThirty-Something, 502 powered
 
Posts: 7397 | Location: AZ Central Highlands | Member Since: 01-09-2001Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 2/16
Captain Doom
Picture of Rusty
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I got a reman QJet for the SOB from National Carburetor and was very pleased both with the product and the service.


Rusty


MilSpec AMG 6.5L TD 230HP; built-to-order by Peninsular Engines:  Hi-pop injectors, gear-driven camshaft, non-waste-gated, high-output turbo, 18:1 pistons.  Fuel economy increased by 15-20%, power, WOW!"StaRV II"

'94 28' Breakaway: MilSpec AMG 6.5L TD 230HP

Nelson and Chester, not-spoiled Golden Retrievers

Sometimes I think we're alone in the universe, and sometimes I think we're not.
In either case the idea is quite staggering.
- Arthur C. Clarke

It was a woman who drove me to drink, and I've been searching thirty years to find her and thank her - W. C. Fields
 
Posts: 8370 | Location: Brooker, FL, USA | Member Since: 09-08-2005Reply With QuoteReport This Post
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A cautionary note on well-used (high mileage) QJs: They are prone to eventually enlarge the openings in the casting -one on each side- where the pivot pin for the butterflies is supported. This is not noticeable, but once it starts it enlarges and ruins the venturi effect in the carb. If it runs rough/unevenly, eyeball the pin support.


"You are what you drive" - Clint Eastwood
 
Posts: 573 | Location: Republic of Texas | Member Since: 12-31-2004Reply With QuoteReport This Post
First Month Member
Supporting Member of Barthmobile.com 11/13
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quote:
Originally posted by Gunner:
A cautionary note on well-used (high mileage) QJs: They are prone to eventually enlarge the openings in the casting -one on each side- where the pivot pin for the butterflies is supported. This is not noticeable, but once it starts it enlarges and ruins the venturi effect in the carb. If it runs rough/unevenly, eyeball the pin support.


Anybody interested, I got a fix for that that is less work than rebushing. Rebushing requires a lot of precision setup.


.

84 30T PeeThirty-Something, 502 powered
 
Posts: 7397 | Location: AZ Central Highlands | Member Since: 01-09-2001Reply With QuoteReport This Post
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I've been having a very similar problem. I also replaced the paper filter, but the problem remains. I lose power when the motor gets warm. We're planning on heading to Albuquerque next week and I don't want to be sitting along the road. Any help is much appreciated.


1986 Regal 25ft.
454 Chevy
 
Posts: 33 | Location: The Great American West | Member Since: 04-25-2009Reply With QuoteReport This Post
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Supporting Member of Barthmobile.com 11/13
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When you say you replaced the paper filter, do you mean the little one at the carb inlet?

How about the one under the coach near the entry door? It is also paper, but can be inside a clear plastic, white plastic or metal can.

Do you lose cruise power or just the ability to accelerate?

Does the engine stutter or jerk?

Is there any popping in the intake or exhaust?

Does it shoot flames out the exhaust?

Does it lose power with the gas cap removed?

Is the heat riser free and is the spring working?

A coil will act up when hot. Unfortunately, that is difficult to troubleshoot without an Allen scope or similar. I carry a spare coil and ignition module. Delco brand is best.

How are your ignition wires? If you have an ohmmeter you can test them, but, again, something that acts up only when hot might test OK not hot. I would replace the right rear lead anyway, unless it was very new, just because it fails first.

Look inside the distributor cap for red dust or frozen advance flyweights.

How is the float level? If it is low, the engine will run OK with the choke on, but will lean out as the engine warms up and loses the enrichment offered by the choke.

Check all the vacuum hoses. Several are connected to heat sensors and can affect hot running. I would just replace them with the orange silicone hose sold by NAPA. It takes the intense doghouse heat better.

I haven't had my coffee yet, and gotta run, but maybe I'll think of more later.


.

84 30T PeeThirty-Something, 502 powered
 
Posts: 7397 | Location: AZ Central Highlands | Member Since: 01-09-2001Reply With QuoteReport This Post
The Old Man and No Barth
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My Regal lost power going uphill. I replaced all the fuel line filters, two in line under the coach, plus the little thingy at the carb. Problem solved.

I've tempted fate twice, & rebuilt Q-jets; once in a Chevy Suburban, once in a boat. Succeeded both times.

I once had a Chrysler New Yorker from the early years of the economy craze. It had a 440, and a beautiful Holley 4-barrel, but it was gutless, and regularly blew out diaphragms. I went through the carb, & made some changes, though I no longer remember what. Car went like gangbusters afterward, but economy went from merely lousy, to atrocious.

Sold it to a guy who had a Mopar pickup that overheated when he pulled his travel trailer. He came back a couple months later & I was afraid he was going to kill me, but he thanked me profusely for selling him such a wonderful trailer-tower.

I agree with El Segundo Bill on his preference for the Q-jet on stock vehicles, but it can be a trial to reassemble the lid, with all the stuff hanging down that has to be delicately guided into small holes on pain of bending something.
 
Posts: 1612 | Location: Upper Left Corner | Member Since: 10-28-2002Reply With QuoteReport This Post
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A couple other ideas: check the vacuum advance springs in the distributor. Check ignition timing. The timing mark will be visible on the harmonic balancer from underneath. That archaic tool called a timing light is helpful!

If the springs are original, they may warrant replacement. Also to reiterate, the vacuum line integrity is very important.

good luck!
Matt


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Gibson Exhaust
 
Posts: 320 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 2/16
Captain Doom
Picture of Rusty
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Also check to see if the heat riser valve is stuck open.


Rusty


MilSpec AMG 6.5L TD 230HP; built-to-order by Peninsular Engines:  Hi-pop injectors, gear-driven camshaft, non-waste-gated, high-output turbo, 18:1 pistons.  Fuel economy increased by 15-20%, power, WOW!"StaRV II"

'94 28' Breakaway: MilSpec AMG 6.5L TD 230HP

Nelson and Chester, not-spoiled Golden Retrievers

Sometimes I think we're alone in the universe, and sometimes I think we're not.
In either case the idea is quite staggering.
- Arthur C. Clarke

It was a woman who drove me to drink, and I've been searching thirty years to find her and thank her - W. C. Fields
 
Posts: 8370 | Location: Brooker, FL, USA | Member Since: 09-08-2005Reply With QuoteReport This Post
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quote:
I lose power when the motor gets warm.


Brady & Hilary! Do you try to get power from the motor when it is cold?

I'm also wondering about the spark plugs. Even if they are young in terms of miles, just the fact that they have been in the engine for perhaps many years will have degraded them. The dielectric of the ceramic changes, microscopic fissures in the ceramic bleed the spark charge, and if you have a rust stain on the plugs (like mine did at one time), you will have a path of least resistance which will partially ground out the spark charge. It might not show up at lower rpms, but at higher, it does.

Keep us updated on your status!
Matt


1987 Barth 27' P32 Chassis
Former State Police Command Post
Chevrolet 454
Gibson Exhaust
 
Posts: 320 | Location: Massachusetts | Member Since: 07-28-2006Reply With QuoteReport This Post
Picture of Brady and Hilary
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Yes, the filter I replaced was the one at the carb inlet and I had a heck of a time finding the inline canister due to the fact that the fuel line is 1/2" at that point. I finally found one and I'm going to install it and hope that fixes everything.

The problem, to be more specific, seems to be after the motor gets hot it "bogs down". I think that's the best way to put it. especially under load going uphill. I push the accelerator and it sounds like it's flooding out or something and I've got barely enough to get up the hill.

I will check the plugs, wires and cap. I'll probably just replace them.

The heat riser? I think this has been disabled. The return lines from the exhaust manifold were literally rotting off. My mechanic thought it was a lost cause and took them off and welded bolts into the holes on the manifold. Wouldn't that only effect cold start ups though?


1986 Regal 25ft.
454 Chevy
 
Posts: 33 | Location: The Great American West | Member Since: 04-25-2009Reply With QuoteReport This Post
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