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Carburetor Issues for a 59 w/390ci

Started by Ed Burke, November 15, 2017, 03:46:03 PM

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Ed Burke

I have the original 4 JET Rochester on my 59 with a 390 ci engine. I had this rebuilt about a year and a half ago. It has been nothing but a headache. Now it loads up and fouls the plugs. Besides rebuliding it again does anyone suggest replacing it with a more reliable aftermarket. The car is all original but, original is getting really irritating.

The Tassie Devil(le)

Fouling plugs doesn't come from a carby, but either incorrect fuel, or oil fouling from bad oil rings.

I have found that using the highest octane available at the pumps here is no good for carburettored engines.   It fouls plugs, and makes the engines run rough.   Here we have 91, 95 and 98.   Oh, and that horrible E10, and even horribler E85.

When I ran the 98, I couldn't understand why the engine was performing so poorly, and as soon as I changed to 95, it perked right up.   Turns out that E98 is designed for the latest range of high-end vehicles running EFI, Computers and higher compression.

Bruce. >:D

'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Dave Shepherd

If it is flooding/loading up, either the metering rods are stuck, the float level is too high, a float is sunk,  or the needle and seat is leaking, this assumes it is tuned properly, and firing on all eight. The carbs can be somewhat difficult to get the float level and drop correct, done wrong they can bind on the float housing.

m-mman


Just swapping to a (new) aftermarket (Holley? Edelbrock?) will not be a simple and easy fix.

Linkages wont automatically line up (Dont forget the trans and cruise linkage adjustment?) and the air cleaner wont necessarily fit.  Sometimes a shortcut can sent you down a long and torturous path.
1929 341B Town Sedan
1971 Miller-Meteor Lifeliner ambulance
Other non-Cadillac cars
Near Los Angeles, California

CLC #29634

Dave Shepherd

Seconded, no reason not to correct the carb issue.

Ed Burke

Thanks! I have it off the car now and will look for all this stuff.

As far as the fuel I am using a 91 octane ethanol free gas. The shop manual states it needs 94 so I boost it a little with octane boost. I stopped adding lead. It just made things worse and it smelled bad. I read in more than one place that the lead isn't  really necessary for the valve guides. Any opinions?

The Tassie Devil(le)

The idea of lead in petrol, and it isn't actual lead as in fishing sinkers, but a liquefied form, and it is there to soften the impact of the exhaust valves hitting the seats when they close.   Nothing to do with Valve Guides.

Without some form of protection, the seats will eventually wear away, and it is the reason for fitting hardened seats when doing a head reconditioning job.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Ed Burke


fishnjim

If it's too rich, it'll foul all the plugs.   You should also see black soot inside your tail pipe.
If one or two plugs only or varying degrees of fouling, then it's something else.   
So check the ignition system first, to make sure you don't have a weak spark issue*, then address the carb adjustments.   Make sure the float(s) is shutting off the gas at the right height and not overflowing.  The needle valve has a rubber tip and if the wrong material for modern gas, mush.   The accelerator pump lever has to be in the right hole.   Linkage needs to be checked as well, that it's installed right way.
It could be something other than the carb, vacuum advance not working, etc.   I'd take to a shop that has an exhaust gas analyzer for the fuel ratio adjustment.   It's more difficult to get it right, by ear, with the modern fuel.   Plus you can test at different rpms.
I concur an off the shelf Edelbrock, Holley, or similar most likely won't fit the air cleaner.   You have to adapt for the different diameters.   You can buy adapter online.   The Edelbrock performer is basically an AFB, so they fit the stud pattern, linkage, etc.   I had to get a linkage connector for the transmission rod as the person that changed carbs didn't hook up the trans rod.   But I've since converted to 3x2 after the rebuild so history.
Unless you're from this era, you can't really appreciate why all this stuff was changed over time.  You'd go out to go someplace and it would start.   So you had to spend a half hour under the hood, usually it was cold outside also...  Plus today the people that were good at fixing are disappearing.   I was ecstatic when they went to electronic ignition.   No more points to mess with.  Fuel injection even the first few years beats any carb**.   The only thing that was wrong with TBI early on, is if it failed, you were DOA tow truck bait.   At least you could limp home on a sick carb.
* - The pertronix stuff works nice in these applications.
** - something to consider, you can probably get a TB setup for under 2 grand.

Ed Burke

Thanks for the detailed response! I'm 56 years old so I do have memories of limping home in my second hand cars from the 60s and 70s.
I rebuilt the carb today. Floats measured good and seemed to move freely. I'm using ethanol free gas so I am hoping that helps the rubber inside. I plan to drop a Petronix in soon. I'm sticking with the carb for now. I'm trying to keep it as original as possible.
I checked the plugs. Two were blackish. The rest were brown.
The compression check revealed  6 cylinders were not up to par, but acceptable.
I'm not sure who could tune the carb around me. Most guys never worked on them. I have the shop manual that describes it in detail, but I'm not sure they would take on the challenge.

savemy67

Hello Ed,

Your post doesn't mention the mileage on your car, only that it is a '59 in original condition.  Many people experience driveability issues with old cars, and consider swapping factory components with newer, aftermarket components.  I would like to suggest that a 58 year old car, though original on the outside, may not be original inside the engine (unless the engine and all components have been recently rebuilt).  Even the best rebuilt carburetor will not overcome problems with an old engine that has valve issues, timing/ignition issues, or as mentioned in your post, concerns about compression.  My suggestion is that looking at only one component of a 58 year old car may not be sufficient when it comes to driveability issues.  Looking at all the systems related to driveability may pay off in discovering a condition that may not be obvious.

I applaud your rebuilding of the 4GC.  In addition to the shop manual, H.P. Books Rochester Carburetors (ISBN 0-912656-10-7) may be a useful additional resource if you can locate a copy.  There is no reason that a well functioning 4GC needs to be replaced on your car provided all else is in good shape.  Good luck.

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

curly

#11
ED, after years of messing with my AFB, I could never get the accelerator pump system working. So when I had the engine rebuilt I installed a new Edlebrock 1406.  I got around the accelerator linkage and Throttle rod problem by transferring the carb linkage from a spare carb.  I did install an open element air cleaner as the factory one no longer fits. It doesn't matter to me because I don't show the car but I do drive it. I can return it original in about 30 minutes.
Edit: I also had to add a throttle stop/idle screw stop since the AFB didn't have one. A simple metal bracket - L shaped - took just a few minutes to make and attach to the throttle lever.  It's the top bolt in the pic below.  You can see the idle speed screw behind it.