Hello all from Brisbane , Hope everyone is well. I have had and issue with the 4 gc carby, on my 58 olds. Its been going on for some time and has got me into a tight spot more than once, This might sound strange but when i drive the car off at a set of lights and turn to the right and give the car some gas the car dies as though it's not getting any fuel, but it seems to be fine when i turn to the left,? and also it drives fine in a straight line. I thought it might be a float touching the side of the bowl etc so i have taken the top lid off the carby and had a look at the floats.etc and they seem to line up ok. I checked the float drop setting from the shop manual and it said to set the float drop at 1 / 1/2 " from the underside of the lid including the gasket to the dot on the side of the floats. i did this and installed the lid connected fuel line , started car and it started flooding and sending fuel onto the intake manifold. I must be setting the float level wrong or something as i checked the needle and seats and there was no debris etc on the needle etc.Any help with the setting up of the floats levels would be great, I guess there is some secret to setting these floats. One guy told me to turn the lid upside down and measure the float distance that way, Im a bit lost as to what to do, many Thanks in advance for any replies, Sorry about the long winded question, Cheers, Ray aka piperman60

 

I'm assuming that it is the correct 4GC for 1958; 7012400 for the auto trans or 7012401 for the manual. If so, the Olds shop manual for 1958 has a large section on getting everything set properly. You'll have to go step by step carefully through the process. If you're getting flooding and fuel on the intake manifold something is obviously amiss. Be careful of fire with a lot of fuel outside the carburetor. Pay close attention to the power piston/vacuum assist mechanism on the primary floats. This can cause problems if not working correctly. And be sure to note that primary and secondary float setting dimensions are different. Best wishes.

 

Hi there Ozzie, Cheers for the reply. Yes the carburetor is the 7012400, i have the tag on it. i took a couple of pics this afternoon with ruler etc against floats and the pics from the shop manual, Hope i have it right ? I put the carb back on and started the car ,seems to not be flooding but i can bet it's not right , I will go for a drive tomorrow and test it.

 

Hello Ray.

The float drop setting ensures that the needle pulls far enough from the seat to allow adequate fuel into the bowl. Too much drop and the needle could get out of the assembly. This does not seem to be the problem with your car.

By your symptoms, you should be adjusting the float level. This regulates the level of the fuel in the bowl.

Cheers,
Gary

 

Hi Ray,

In case it might help some, I photographed some of the pages from my Rochester carburetor book which applies to the 7012400. Sometimes an alternate explanation helps. I had to do it with a camera as my scanner is on sick leave. I hope it is readable. If not, let me know and I'll try again.

Bulletin 9-OL-1; OLDSMOBILE; June 1965; page 3


Bulletin 9-OL-4; November 1964; page 1


Bulletin 9-OL-4; November 1964; page 2


Bulletin 9-OL-4; November 1964; page 3


Bulletin 9-OL-4; November 1964; page 4

 

Specific gravity of fuel can actually effect float level. so can fuel pressure. Most carbs do have a psi range, I'd say 5-6 psi on your 4GC. You should also do this quick test if you have brass floats to make sure they are serviceable.

 

Hello again, Just a quick update on the float level issue on the 58, I have for the last three days started up the car , In the past i would have to pump the gas pedal a few times to get some gas into the carburetor then start the engine but since i have adjusted the float level no pumps etc, the engine starts right up first turn of the key.no flooding etc That's the good news, Now for the bad, Yesterday i took the car out for a drive, It ran really well, no hesitation on corners etc. I drove for around 20 minutes with no issues. I was about a mile from home when the engine started running really rough, no backfire etc nearly stopped on me at the lights. it was like it was only running on 6 or 7 cylinders and the generator light was flashing on and off, I managed to get to my front gate and got out to open the gate and the engine would hardly idle as well as the generator light coming on. I let the car cool down and pulled all of the spark plugs as i thought they may be dirty etc. Cleaned them all and put back in but the car still runs rough, like a couple of cylinders are out, Also if i rev the engine the generator light will go out! so i figure the generator must be ok ? Just wondering if there could be a issue with the coil ? I will replace plugs as they have been in the car for over a year., It just seems really strange this has happened as the car was running great!!, Any idea's Please, Thanks, Piperman60,

 

The generator light is probably coming on due to the slow rough running of the engine and has nothing to do with the "real" problem. There are many things which can cause what you describe; usually either ignition or carburetion, but can even be an internal engine problem. You'll have to check most things and try to verify individual component performance. You can "ground out" the spark to each cylinder one at a time to try to determine which cylinder(s) are causing the problem. The ones that make none or very little difference are the problem cylinders. You can check the spark plugs in a tester or move them between cylinders to see if the problem moves also. You can check the spark plug wires with an ohm meter. Look at the distributor cap for cracks or carbon tracking. Condensers can cause problems. I once had a new condenser that wouldn't allow the engine to start. If the points are clean and gapped properly they usually won't do what you describe. You can check the coil's primary and secondary sides with an ohm meter, but that might not tell the "whole story". Substituting a known good coil is probably best. A compression test is a good way to determine the internal health of the engine. However the sudden change makes me think that is likely not the problem unless something broke (like a valve spring). Try to figure out which cylinder is not "pulling its load" as described above. That will help you to isolate the problem. Best wishes.

 

I think Ozzie hit all the main points could be any of them but to me I would check the points for pits or craters. I have replaced more coils, caps and condensers only to find out it was the points all a long. Just a thought and a guess from afar.....Tedd

 

Depending on the mileage, if it has a nylon coated timing gear it may have skipped a tooth or 2. There is a way to manually turn the crankshaft back and forth while watching the distributor rotor. Depending on how much slop is in the timing chain the dist. will move a certain amount. The original nylon coated gears can break and there goes your timing. The broken pieces end up in the oil pan and clog the pump screen. I'd also do a compression test to make sure the engine is sound.

 

Hello again all,, just an update on the engine rough idling issue, I replaced the points as they were worn nearly right away, also changed the plugs, set time timing again to 8 Dgs, and dwell to 17 and the engine runs great, combo of bad plugs and points and the 371 doesn't like it at all, just another learning curve for me, Still have an issue with the carburetor though turning to the right etc, I'm going to lift the float level slightly to try and stop this annoying issue but all in all new pugs and points and i'm on the road again, Many thanks to everyone for your help and comments, I'm going to rebuild the power steering pump and box over the Christmas break as i have a couple of car shows i'd like to drive to before then. cheers again, Ray.

 

This would not be an issue in a '58 Olds .
Nylon toothed timing gears were not introduced until 1965 or so .

 

Do you mean you set the points at .017" and not 17 degrees dwell ?

 

I set the timing to 9 Dgs and the dwell to 17 Dgs.

 

??

Those setting appear different than what is published for either a 6-cyl or a 8-cyl.

http://www.tpocr.com/olds.html
http://www.carnut.com/specs/gen/olds50.html

 

Sorry ,Yes I set the timing to 9 degs and the dwell to 29 degs the dwell was originally 17 the workshop manual said between 28 to 30 for dwell

 

29 degrees sounds much better.

 

Hello again from Brisbane, Just an update on the issue i have been having with the carby in my 58 Olds. Last weekend i took the car for a drive and it ran fine until it got to normal running speed, then started to surge again at around 40 to 50 mph. As i have replaced plugs and points and fuel filter and set timing and dwell angle i'm thinking maybe the issue could be the fuel pump.We had the engine idling smooth before i drove it. I took the car for a drive yesterday and it seemed to be running very rich so i tweaked the mixture screws a bit but to no avail. It was running so rich it was burning my eyes, I'm at a loss so i'm taking the carby to get checked out, maybe floats are still set too low ? not sure ? very frustrating,Might look at another carby but not sure about all the linkages etc. Will keep you posted, Cheers, Ray.

 

I merged the new thread you started back to the original to have all the info history in one place.

 

Hi again, took off the carburetor today and removed the lid with floats attached, both fuel bowls were 1/2 to 3/4 full of fuel and still had pressure in the fuel line so i don't see that it could be lack of fuel making the engine surge when it's at running temp, I'm going to try another coil as it maybe cutting out once it gets hot. ? from looking at the coil it looks like the original one. Any thoughts please, Cheers.

 

What do the spark plugs look like? Black and sooty or tan?

 

Hello, I took out one of the plugs, What do you folks think, Cheers

 

Did you set the timing first, then set the dwell? If so, your timing is way off now.

Set dwell, then set timing--in that order.

 

It looks wet.

 

I took the carburetor to the shop today and told the guy about burning eyes from fumes etc and the surging and straight away he said it sounds like it's running too lean, he's going to set float level etc and once i put it back on the car he will take another look at it.

 

I am having the same problem with my 4GC carburetor. 1962 Oldsmobile 394 engine runs well but wants to die when turning right but only when driving every built the carb and tried to set float levels. Car runs perfect other than this issue. Would love to know if the Aussie got it figured out.

 

hello there, I took my Oldsmobile to a guy who owns a business called Carb Tech, he’s an old school Carby guy . He Charged me $100 . He tweeked the carburettor and told me to take it for a ride around the block, my god it was such a dramatic change, it idled beautifully runs like a dream , no stalling at traffic lights etc ! He told me there’s a lot of guys out there that think they know how to adjust a 4GC but it’s finding one that can! I’ll try to get some details for you and maybe email him? Cheers , all the best, Oldsmobiles, gotta Luvem

 

I have a ‘58 371 with a 4gc. It runs well…….except has a big sag on right turns!

I have been assuming it is something amiss with the float(s) but have been reluctant to get in and tinker——not sure if I need to add or subtract from float level and hate to just guess.

if you learn what your carby tech guy found on your car and can share it I would be “all ears”!!

thanks

 

I had the same or similar problem on my 1964 Chevy Impala with a completely rebuilt original numbers matching engine and transmission that was completely taken apart and meticulously gone thru every but and bolt by hand to ensure it was all done right and nothing was missed... couldn't figure out why when I would turn quickly or make a really wide turn sometimes my engine would just instantly cut off and die while in the middle of the turn! It was very dangerous and scary and I had a few near accidents that luckily were narrowly avoided. It was so weird, it drove fine going straight and most of the time, just when turning a big turn or fast going into a turn the engine would just die completely and I'd have to try and re start it before I crashed since the power steering goes out when the engine dies and it is a heavy car, so it was hard to maneuver once the engine would cut off mid-turn! Ended up turning out to be 2 different things, one was the fuel filter, check it make sure its not rusted or coffee up with any gunk, I would blow through it to get any blockages out of the filter so it can really gulp the fuel down easily when it wants to instead of sucking to squeeze out a few drops of gas through the huge mess of gunk blocking the filter almost completely so only a small tiny stream of gas was getting through at any one time. So when I would hit the gas hard and try to really give it some power, it was struggling because it couldn't get the amount of fuel it needed quick enough since it was only soaring through a tiny little hole that was free of gunk and rust debris like the rest of the filter was clogged with..... also the other thing was that my dad had changed it a part on the carburetor for me, trying to help me out and do me a favor without al my knowledge, he thought he was upgrading a part for me but he accidentally got the wrong size, which is what was actually causing the specific problem of engine dying when in the middle of a big turn. I forget what the last was. I'll think about it and update this post once I remember the exact part that was the wrong size that was causing the engine to cut off when making a turn.