Question
Throttle side
Hello Mr.Benjamin
I've got a 1964 Chevy Impala that I purchased about a month ago that I'm having some problems with. The number on the carb is 7024121, which is supposed to be a Rochester 4G or 4GC, but after reading the manual I've found, I've realized that the carb does not match the number (there's only 2 screws on the front, the fuel accel pump is wrong, etc).
I've got a few pictures that I will attach. I was wondering if you could tell me if you recognize it, or if you can tell me if you can see the fast idle/slow idle/air adjustment, and so on. I've worked on a 2 barrel carb before and got the hang of making the engine run nice by the sound of how well the engine is running, but on this carb there are only 2 screws, and I'm pretty sure they're only air bypass screws (the two on the front).
I'm sure the problem is simple adjustment, because when I hit the gas while in gear the engine chokes out unless I press VERY lightly, just enough to let the engine start revving up, then release the gas and then quickly hit the gas to about 1/3-full throttle. When i do this, the car will accelerate nicely, and stay working perfectly as long as I don't slow back down to a full stop.
Another quick thing that is wrong is that when braking (driving around the yard) the brakes do not apply until they are almost at the floor, and then they apply, the car pulls to the right, then half an inch more to the floor, and pressing hard locks up the brakes. I've bled the brakes (the front comes out clean, the back is still coming out a bit dirty), but haven't looked at the actual drums yet. I was wondering, if they are rusty, would it be alright to clean them with a wire wheel? Or even soak them in muriatic acid to clean them?
If they can't be cleaned I'll probably be putting disk brakes from a monte carlo or the like on. Any suggestions on a good donor car?
Oh! I should tell you that the car has an electronic ignition, and a master cylinder for the brake system. When I take the vacuum assist hose off the brakes, the engine sucks air and increases RPM, which leads me to believe that the bladder in the master cylinder is in tact (could I be wrong?)
Any advice on any of this would be greatly appreciated. I have more pictures of the carb, but can only upload one.
Thank you very much for your time.
AnswerI see many familiar features on your carburetor, since the cars I collect also use 4GC carburetors, but each application has minor differences in locations of adjustment screws and fuel inlet fittings.
The idle mixture screws are always in the same place on 4GCs, as far as I know. There are always only 2 of them - there is no idle circuit for the secondary barrels (the rear ones). The screws are on the front of the carburetor, down at the very lowest part of the carburetor, just above the surface of the intake manifold. You can't see them without getting your eyes really low or using a mirror.
They are brass screws, with springs wound around them, and if you take them out you will see that they taper to a needle point. The proper setting for these is to run them all the way in (GENTLY!!) until you feel them bottom out, then back them out about 2 turns. Then, with the engine idling, try moving both screws in or out about 1/8 turn at a time to optimize the idle speed and smoothness. If you cause a big increase in idle speed, you need to correct the curb idle back to 600 RPM in neutral, (or 550 in drive if your car is automatic), and then fiddle with the mixture screws again to see if you can further improve the idle.
4GCs often have a problem on acceleration. The symptoms you describe are what I am used to hearing when someone has this problem. The problem is caused by the leather of the accelerator pump drying out - this always happens when the car has been left sitting long enough that the gas evaporates out of the float chamber. The only cure for this is to replace the accelerator pump plunger. Buy the rebuilder kit for the carburetor and follow the instructions for cleaning it out and re-assembling it. It isn't rocket science - just follow the instructions, read them carefully, study the diagrams and double check your work. All you need is a clean, well lit place to work and normal hand tools, plus a spray can of carburetor cleaner (Gunk is a good brand).
I see a modern HEI distributor on your car - this is 20 years too new for the car - and is calibrated for a much later engine - once someone has modified an engine in this way, it is very difficult to troubleshoot it - because we don't know what has been fiddled with - so I can't be any help to you there. It would be nice if you could find the correct distributor and anything else that has been "improved" and put the car back right. These cars ran extremely well when they left the factory, and will again if everything is put back right.
The brake component that accepts the vacuum hose is the power brake unit, not the master cylinder. Your test shows that it is not leaking vacuum, which is good, but it could have other problems. It could be the original type - I can't see it in the picture. The original brakes worked just fine when everything was correct and in good shape in the brake system. From your symptoms, I can only guess at what is wrong - I think you should take the car to a brake shop that has been in business for at least 20 years, is locally owned (NOT A SHOP THAT you see ads for on TV!) and let the mechanics that have grease under their fingernails and dirty overalls fix it for you.
To answer your questions, there is no need to remove rust from the brake drums - they will clean up automatically when you get the brakes working right.
A sudden lock up of a wheel is almost always due to a contaminated brake lining, which means either a grease seal or a wheel cylinder is leaking, and once the lining is contaminated, it is ruined, so you will need new brake linings (but first find and fix the leak).
The pedal going too low means the brakes are not adjusted right. Perform the typical brake adjustment and see what you have then (tighten the adjuster until it locks each wheel, then back off 8 clicks). If you still have the pedal going to the floor, there is a problem with the master cylinder. Replace it - they are cheap and easy to change.
If you want the car to be safe, replace all 3 brake hoses also.
Dick
