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Tech Editor's DeskProjects, papers, writings, thoughts, musings of our technical editor Joe Padavano. To begin with, he will be making threads and can approve posts to it if he wishes. This can be changed in the future if it does not work out well.
The Rochester 4GC was Oldsmobile's main 4 barrel carb from 1952 thru 1965 .
It was replaced by the "spread bore " Quadrajet carb in 1966 .
The carbs all appear pretty much the same externally , but the earliest carbs had small throttle bores and venturis . These got larger as the carbs were used on larger engines through the years . The F-85 and Cutlass versions also had small throttle bores and venturis .
In this article I'm rebuilding a 1963 Olds Starfire 4 GC ;
The first thing we need is a carb rebuild kit . In the previous picture you will see a three cornered tag , attached by an airhorn screw . That tag has a seven digit number that tells the exact sub-model of carb you have .
Note this number , as it may be useful when ordering kits or parts .
If it's missing , don't worry , most carb kits have enough extra gaskets and parts to fit almost all 4GC's .
1952 and 1953 Olds owners be careful when ordering parts . Some 52 and 53 's had a Carter WCFB carb . They're easy to identify , it says "Carter" right on the carb .
That carb is completely different from a Rochester 4GC .
The carb kit will have an instruction sheet like this ;
This will have a complete illustrated breakdown of the carb .
To start dis-assembly , start with part number 1 and go right down the list until the carb is completely stripped.
Here are some things of special note when dis-assembling .
Double nut the aircleaner stud when removing ;
And then there's the "secret screw " . There are 13 screws that hold the airhorn to the main body . The thirteenth is at the top of the airhorn where the screwdriver is shown ;
Also take note of the size of the jets . The primary side (with the choke) jets are smaller than the secondary .
Also the "screw starter" is really handy for installing jets .
And speaking of jets . If you're going to be running ethanol laced fuel . The carb jets need to be a step or two richer . The jets have numbers on them .
The jets in this carb were #54 (primary) and #84 (secondary) . These were replaced with #55 (primary ) and #86 (secondary) .
Carb jets (as well as many other 4GC parts ) are available from Daytona Carburetor ; https://daytonaparts.com/
One other thing , the hose nipples looked almost the same except for a line on the side . turns out the two had different restrictor hole sizes . Make sure the same parts go back in the same place .
The pump discharge ball retainer is removed with a pair of needle nose pliers ;
There is also a ball in the bottom of the accelerator pump well . Take note of what size ball comes out of where . The kit will probably come with new ***** , but you need to know what size to put where .
One more thing , save as much of the old gaskets as you can.
At least enough to compare with new gaskets to make sure all the holes are in the right place .
There will typically be more gaskets in a kit than you will use . Make sure to use the right ones .
Once it's all dis-assembled , then it must be cleaned.
It's best to use a "dipping solution " . This one gallon one came from O Reilly's ;
The gallon can was too small for several parts , but by using a shallow plastic pan from the dollar store I was able to soak the larger parts . Brushing the parts with an old toothbrush will help remove dirt . Best to soak parts overnight . Use rubber gloves .
The cleaner can be rinsed off with water and then blown dry with compressed air.
Now it's time to put things back together . Just start with the last part on the list and work your way back to #1 . On the instruction sheet there are several adjustments that will have to be made as you assemble the carb ;
Also , there is a data sheet that shows the adjustment specs for your car .
As you can see , this kit probably fit many different cars.
A small paper ruler is usually included which aids in many adjustments , as in this float adjustment;
A handy carb stand can be made from four 5/16 bolts and nuts;
After careful assembly and adjustment , this should be your final product;
Last edited by Charlie Jones; November 8th, 2021 at 07:35 PM.
Charlie, a great article with great pics as usual. One question, I have not seen the recommendation to change jet size due to ethanol fuel before, what is the basis for that?
One critical step: MAKE SURE YOU PUT IN THE CORRECT THROTTLE BODY TO FLOAT BOWL GASKET.The wrong one will make a 4GC do all sorts of hateful things due to differences in vacuum passages.
Charlie, a great article with great pics as usual. One question, I have not seen the recommendation to change jet size due to ethanol fuel before, what is the basis for that?
Tony Lombardi at Ross Racing Engines told me to do that .
Alcohol has less heat content per gallon than pure gasoline . Therefore a slightly richer mixture is required .
Charlie, I came across this post on another website by Cliff Ruggles. Keep this in mind if you have trouble after using fuel with ethanol added I don't know if there is an alternative float for the 4GC. Good luck nice rebuild
NEVER for any reason use a brass float, they are too heavy, and this fuel eats the solder up in them and they will sink to the bottom of the bowl.....the failure rate on the current production brass floats is 100 percent. We found this out here the hard way a few years ago, as we also rebuild AFB's and other types of carbs that use brass floats. One by one they all came back, some were out there a couple of years, some a few weeks, but every single brass float we installed failed and filled up with fuel and sank.
Charlie, I came across this post on another website by Cliff Ruggles. Keep this in mind if you have trouble after using fuel with ethanol added I don't know if there is an alternative float for the 4GC. Good luck nice rebuild
NEVER for any reason use a brass float, they are too heavy, and this fuel eats the solder up in them and they will sink to the bottom of the bowl.....the failure rate on the current production brass floats is 100 percent. We found this out here the hard way a few years ago, as we also rebuild AFB's and other types of carbs that use brass floats. One by one they all came back, some were out there a couple of years, some a few weeks, but every single brass float we installed failed and filled up with fuel and sank.
NEVER for any reason use a brass float, they are too heavy, and this fuel eats the solder up in them and they will sink to the bottom of the bowl.....the failure rate on the current production brass floats is 100 percent. We found this out here the hard way a few years ago, as we also rebuild AFB's and other types of carbs that use brass floats. One by one they all came back, some were out there a couple of years, some a few weeks, but every single brass float we installed failed and filled up with fuel and sank.[/QUOTE]
I have had my car more than 6 years with the Oem 4GC and have rebuilt it twice. All of our gas has ethanol but the floats look fine with no problems. Also don't understand the "too heavy" comment....
Charlie, I came across this post on another website by Cliff Ruggles. Keep this in mind if you have trouble after using fuel with ethanol added I don't know if there is an alternative float for the 4GC. Good luck nice rebuild
NEVER for any reason use a brass float, they are too heavy, and this fuel eats the solder up in them and they will sink to the bottom of the bowl.....the failure rate on the current production brass floats is 100 percent. We found this out here the hard way a few years ago, as we also rebuild AFB's and other types of carbs that use brass floats. One by one they all came back, some were out there a couple of years, some a few weeks, but every single brass float we installed failed and filled up with fuel and sank.
Cliff talks about " current production brass floats " (As in Chinesium ?) .
I , myself , have never experienced any problems with original brass floats in over 40,000 miles of driving with ethanol fuel . And I don't think most others do either .
As for " this fuel eats up the solder in them" , I don't believe that .
I believe it's more like a poor soldering job to begin with .
As far as I know , there were never any plastic floats made for a 4GC .
Plastic floats were not introduced until the late 60's . Even the early Quadra-Jets had brass floats .
I too take exception to this blanket statement. If it had validity would not every vintage ride with brass floats in the carb exhibit the problem? None of my rides (55 Cadillac, 62 Oldsmobile, 63 Corvair, 85 Riviera) have exhibited the aforementioned "float problems" and all of them are fueled by ethanol laced gas.
Me thinks the problems were with the floats Mr. Ruggles was using in his rebuilds
As the statement said CURRENT PRODUCTION BRASS FLOATS. I agree with most people that it's hard to fathom that ethanol fuel will effect solder. I posted the statement for people who might experience problems as a probable cause of a rough running. The only way to verify this statement would be to submerge a brass float in ethanol fuel for awhile and see what happens. Sorry for the false flag.
I have looked for brass floats for a Quadrajet because the new fuel eats the foam plastic.
A float that is "to heavy" ? "Current production" ? Those floats in Rochester carbs worked for years and years. The "old" solder had lead in it, not sure whats in new "plumbing"solder.
I am with Charlie.....bad soldering job.
Picture attached of my instructions - appear to be same instructions you have. Which row do I use? I have a 1962 olds starfire. the instructions don't show that one. thanks for your help.
Picture attached of my instructions - appear to be same instructions you have. Which row do I use? I have a 1962 olds starfire. the instructions don't show that one. thanks for your help.
The row that says ; 1958 - 62 all standard . (not F-85 )
Thx. U confirmed. That’s the row i used to set my floats. Spewing gas out the top of carb, and car stalling out when driving. I’ll pull the air horn out and do it again. I assume measurements are from float dimple. Thx again!
Thx. U confirmed. That’s the row i used to set my floats. Spewing gas out the top of carb, and car stalling out when driving. I’ll pull the air horn out and do it again. I assume measurements are from float dimple. Thx again!
SOME measurements are from float dimple . Others are not . Read the instructions carefully . Check both sides of a float as the center connector may be bent .
Do you have new needles & seats ? Have you checked the floats?
The floats can be checked by removing them and shaking them gently . If it feels like there is liquid inside them , they are bad .
New floats can be had from Daytona Carburator ; https://daytonaparts.com/
You mentioned that the airhorn was cracked , did you repair or replace it ?
Thx Charlie. I will re-read the instructions. I had previously checked floats by placing them in water. The carb kit i bought includes new needles, seats, pins, and gaskets - i have put those in. No gas leaking out of the small crack on the side. I will re-check and adjust the float levels. Thx again for all your help.
July 15th, 2018, 11:56 PM
