When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Just picked up a great car that starts right up.
Problem is that it wants to die after a few minutes unless you keep the idle up around 2500.
Starts up...idles normally...then dies. After that it will start but needs a lot of RPM to remain running.
I have ZERO clue how to adjust a Rochester 4bbl.
Any ideas on what to do, adjust or fiddle with?
Thanks.
-peter
I assume that carb has a choke pull off? If so, that’s where I would start looking.
No choke pull-off in the conventional sense, but there is a vacuum-operated piston internal to the choke housing. Frankly, given the fact that this car has been sitting, my money is on crud in the carb.
Thanks for the info Joe.
One thing that I immediately noticed is that the rubber boot over the ...Pump arm?...on the top drivers side is cracked and leaking a bit.
I'll get a can of carb cleaner and hose it down.
-peter
No choke pull-off in the conventional sense, but there is a vacuum-operated piston internal to the choke housing. Frankly, given the fact that this car has been sitting, my money is on crud in the carb.
never messed with one of those style carbs. Just a little before my time.
I went through the one on my 65, at the time (2016) there weren't a lot of places offering a rebuild kit for the one's that came on the 330, think I found mine on ebay
Carb rebuild isn't bad and good if you leave the engine stock, I put a cam in mine and couldn't get it to idle off the idle screw, ended up swapping a 625 Carter AFB from a Buick and ran fine for a bit
I went through the one on my 65, at the time (2016) there weren't a lot of places offering a rebuild kit for the one's that came on the 330, think I found mine on ebay
Don't know about five years ago, but there are plenty of sources today.
I'll add one lesson-learned about the 4GC. I normally have no problems with carb rebuild and adjustment (including the CCC Qjets), but the 4GC that came on my 62 215 just kicked my @$$. I could not get it to run right and finally threw in the towel and bolted on an E-brock (which has been there for ten years now). I attribute this to the fact that my 62 had sat in the NV desert for 30 years and the 4GC uses a cast iron throttle body. In addition, there are several drilled passageways in that body and in the main casting that get external plugs after the drilling process. Any rust or debris plugging these passages is impossible to remove without drilling out the plugs. In my particular case, it appeared that the passage in the main body that refilled the accelerator pump well was severely restricted. That's when I gave up.
Thanks Charlie! That article looks great. I’m a Holley kinda guy normally...how difficult is it compared to one of those?
-pete
It's no more complicated than any other four barrel carb .
Pay close attention to the instruction sheet in the re-build kit .
There are usually several bowl gaskets in the kit . Make sure to compare with your old gaskets carefully .
Make sure there are holes where they should be , and none where they shouldn't be .
My experience with 4GC is they're either good or they're junk. I could never get my blue 64 Starfire's original one to work right, but my issue was choke and fast idle. If the choke worked, it would never kick off fast idle. If it would slow idle the choke barely worked. No in between.
The best 4GC I ever had developed an unstoppable fuel inlet leak. This was before anyone was helicoiling carbs.
As Charlie said, pay close attention to gaskets. The wrong one between bowl and throttle body will make a 4Jet do all kinds of hateful things.
In the 64 CSM I found the Cutlass carb section to be more informative than the full-size section.
Ok...need a little help here.
Disassembled carb, cleaned everything up(tons of sand in the carb), started rebuild and everything has gone pretty seamlessly...until the floats.
First...these floats don't look like any of the other floats I've seen and there's no dimple.(are they original?)
There is just an indented line that runs vertically up the float.
A & B were the pictures I took before disassembly to note where the floats were. The primary and secondaries were definitely at different heights.
Upon reassembly, the instructions said to level the top of the floats to the bottom of the airhorn.(C "Float toe adj. without dimple")
This is VERY different from where the floats were upon first inspection.
SO...
1. If I don't have a dimple...where would I measure from IF I choose to follow the factory specs for float height.
2. Should I just move them to the position noted in C? -OR- keep them where they were
3. I've seen/heard that the primary and secondary floats should always be at the same level...and then I've heard the opposite.
Any help fellas?
-peter
Last edited by Rallye469; April 5th, 2021 at 08:27 AM.
Ok...need a little help here.
Disassembled carb, cleaned everything up(tons of sand in the carb), started rebuild and everything has gone pretty seamlessly...until the floats.
First...these floats don't look like any of the other floats I've seen and there's no dimple.(are they original?)
There is just an indented line that runs vertically up the float.
A & B were the pictures I took before disassembly to note where the floats were. The primary and secondaries were definitely at different heights.
Upon reassembly, the instructions said to level the top of the floats to the bottom of the airhorn.(C "Float toe adj. without dimple")
This is VERY different from where the floats were upon first inspection.
SO...
1. If I don't have a dimple...where would I measure from IF I choose to follow the factory specs for float height.
2. Should I just move them to the position noted in C? -OR- keep them where they were
3. I've seen/heard that the primary and secondary floats should always be at the same level...and then I've heard the opposite.
Any help fellas?
-peter
I didn't know they even made plastic floats for 4 GC's .
I would think they must be aftermarket , and probably 50 years old .
I would ditch them for a set of brass floats .
Both the 1° & the 2° float "toes" should be "flush" w/ the air horn surface. Bend each tang until each float toe is flush w/ the air horn surface (regardless of the picture you took prior to disassembly - follow the CSM diagram). The picture you took of the floats prior to disassembly more closely matches the float level adjustment for a Rochester 2GC (not a Rochester 4GC). I'd make the adjustment as described - toe flush with air horn surface.
EDIT: I guess you're asking what point do you measure from? It would be the "bottom" of each toe. The bottom of each toe should be flush with the air horn surface.
Last edited by Vintage Chief; April 5th, 2021 at 02:55 PM.
That 4GC carb is one of the easiest to rebuild and simpletest to tune. Just go by all of the adjustments in the kit and do not leave anything out. I had one on a 61 Vette that I had modified slightly that would run high 12's/low 13's all day. That was with 283 cubic inches.
Let's gain a different perspective by turning the assembly right-side-up which will better illustrate the float-drop level (which is what you're attempting to adjust/achieve). I prefer the diagram you have have presented (above) which illustrates the toe(s) need to be flush with the air horn surface so the floats are truly "floating" in fuel (rather than bottoming out which may be your condition which is not what you want to achieve). If you can't find it on your own, I can find the stipulated float-drop level for the floats, but honestly I wouldn't get too bent out of shape regarding the float-drop level. If the toe(s) are flush with the air horn surface you should achieve a good float-drop level. There are a couple variables which can influence certain characteristics of fuel flow which can influence how the floats perform, one of which is fuel pressure. But, I'd prefer not to get carried away with the exact float-drop level and make your adjustment with the float toe(s) flush. (I'll end up finding your the stipulated float-drop level when I find the time after I post this right-side up image). Note how far below the air horn surface both of your floats are hanging - you're already well below specs in the float fuel bowl, IMO so they both need to be raised (in respect to float-drop level).
Your 4GC (7025157) is on page 13 and either Fig 4 or Fig 4B. I had another site which specifically illustrated your type of plastic float and the float-drop level dimension, but can't find it - I'll continue looking it may show up.
PERSPECTIVE: From 1952 through 1967 there were over 220 different Carburetors produced by Rochester with the Model Number 4GC (these can easily/readily be validated by examination of various United Delco Rochester Service Bulletins). Unless you're an absolute Rochester carburetor guru, you'd be seriously hard-pressed to be able to thoroughly identify exactly which components and manufacturing build/modifications occurred among all 220 various Model Number 4GC Carburetors. That's a significant number of 4GC Carburetors. These carburetors were not exclusive to GM. I have no idea which Carburetors were exclusive to GM, which division of GM & they were used on Studebaker & Packard.
I tore down my first 4GC in 1984 and I too have never seen one with plastic floats. Seen a couple of bum brass floats though. Am I right you can now get new brass 4GC floats or did I imagine reading that?
Thanks for the replies guys.
After a call to the guys at Daytona performance parts, I was told some ‘65 models did indeed come with plastic floats.
After a conversation with tech they told me to measure from the air horn surface to the bottom of each float...1 7/16’s
I tore down my first 4GC in 1984 and I too have never seen one with plastic floats. Seen a couple of bum brass floats though. Am I right you can now get new brass 4GC floats or did I imagine reading that?
Whether you can get new brass 4GC floats depends on the 4GC Carburetor number. I've seen some brass (for which I don't know which 4GC Carburetor they fit), I've heard others say they are no longer available, and others who say you can find new brass 4GC floats. Again, I believe it depends on the 4GC Carburetor number. After all, there were only 220+ 4GC Model carburetors manufactured.
Thanks for the replies guys.
After a call to the guys at Daytona performance parts, I was told some ‘65 models did indeed come with plastic floats.
After a conversation with tech they told me to measure from the air horn surface to the bottom of each float...1 7/16’s
Bolted it all together and viola!
-peter
Glad you got it.
I believe there were three varieties of floats available (as demonstrated in the .pdf link I provided) - Figs 4, 4A & 4B
Fig 4 is brass
Fig 4A is "Type D" brass (barrel float)
Fig 4B I believe was the plastic variety
Based on your Carburetor number & following the flow of Service Bulletin update numbers, it would appear the plastic floats were employed in the later lifespan of the 4GC.
The dashpot slows the closing of the throttle when you take your foot off the pedal quickly .
If the throttle closes too quickly , it can cause the engine to stall .
It took me 2 of those 7025157 4gcs to get my 65 330 running decent.Both had them plastic phenolic what ever they are.My problem was float sinking ,fuel absorbing into them.I could not find any new ones.
Charlie...how vital is it to proper operation?
It sounds like it could be a problem not having one, but I haven’t seen many of them on rebuilt 4GC’s
-peter
You'll see them on automatic transmission cars .
It prevents engine stalling when the throttle is closed suddenly during low speed operation .
Such as in paralell parking .
February 22nd, 2021, 09:14 AM
