Hey Friends, Hoping to get some help here. I am running across some issues where my Olds is stuttering out upon acceleration. But a little backstory to get up to where we are. For reference, we are dealing with the Rocket 88, so it has the Rochester 4GC carb. Ok. off we go... When I first got the car, it was clear that someone in the cars past was chasing a fuel delivery issue of some sort (not the previous owner, as he bought the car and pretty much let it sit for a year till I bought it, so I can't get much history). There was an old electric fuel pump mounted on the frame rail. When we pulled it off, it was all varnished out, and wouldn't power up. Junk. So we tried the original mechanical fuel pump, having a feeling that it too was crap, hence the electric one. Yup. Also junk. So, I went ahead and bought a basic Mr. Gasket 4-7 PSI, 35 GPH fuel pump, ran new lines from the pump to carb, and brand new hard lines from tank to pump. Fired it up, and boom. We have fuel. We noticed however, we were blowing the seats on the needles, so we pulled the carb top plate off, only to notice 1) The inside was SUPER clean, like someone had already rebuilt it, and 2) In that process, they had the spring on the floats reversed, so it had reverse tension. Flipped them around, popped it back on, and all seemed good! You could let her sit for a week, and without even pumping the gas or choking it, she'd fire right up. Fast forward a few weeks (life got in the way) and we finally got her on all new tires, and back on her feet. The plan was to address the brakes, etc and take her for a shakedown! First trip around the block wasn't terrible. We get on our second trip around the block, and I BARELY would hit the gas, and 'COUGH', nothing. Back to idle, touch the gas a TINY bit, same thing. Literally had to limp it around the block idling. We noticed too at this point we were down a cylinder. At that point, it was late on a Sunday, we were out of time, so I parked it in the garage. Monday, I thought lets pull the plugs and see how they look. Black dry carbon. Hmmm....running a little rich? I cleaned them off real good with a stainless wire brush, put them back in, and went about some slight carb tuning. I turned in the mixture screws all the way, and fired it up. I turned them 1/4 turn till the idle smoothed out, went for another ride. A TINY bit better, but not by much. Now I am at the point where I am wondering: 1) Am I getting too much fuel? I ran the calculation based on HP and BSFC, and I am getting a number around 13-14 GPH: (160 HP x .5 lbs) = 80 lbs/6 lbs per gallon = 13.33 GPH My pump is rated up at 35 GPH... 2) Should I replace the accelerator pump possibly (which I know seems the opposite of too much fuel, but I am not sure where to start at this point) I also plan to replace all the spark plugs. Should I get some that are slightly hotter? Thanks for reading my novel! Always learning new things, and I know this place is a great resource. Just don't want to chase my tail too much, and start spending money where it isn't needed.
For one thing if it fires right up after sitting your carb is leaking into the intake or running over. you need a good rebuilder.
do yourself a favor and get rid of that Mr gasket pump....they are junk get a real electric pump like a Carter 4070 ,or get a new stock mechanical pump or both. find out what pressure your carburetor needs and install a good pressure regulator if needed. clean or replace all the fuel lines and fuel tank. make sure you install a filter before the electric fuel pump get the carburetor rebuilt by someone who knows what they are doing. the pump you installed says it puts out 7 PSI...i'm guessing you need somewhere around 5 psi ? find out for sure not sure what the problem is, but eliminate the basic stuff first before making any changes
The pump is ranged at 4-7 PSI. All lines are new, and I have a new inline fuel filter before the fuel pump. Agreed, trying to eliminate basic stuff for sure. I will check that as well! That is one thing I am trying to figure out. I am seeing that some fuel pumps at 4-7 PSI will be as high as 72 GPH. Regulators always talk about PSI, and not GPH....so that part is confusing me a little.
Check to see what pressure is recommended for the carb. A stock pump might be better in terms of getting the right amount of pressure. You can get a gauge/regulator as well. 4 to 7 pounds could easily be too much. Best of luck chasing your gremlin. But I think the first place to lok is the acc. pump and then the leaking into the manifold suggestions.
Just get rid of the electric pump and get a new rebuilt factory mechanical fuel pump. Then if the car is still running rich, work on the carb. There are tons of threads here on the Hamb with carb trouble after installing an electric fuel pump. A new rebuilt mechanical pump will handle the damn corn gas, so don't get a NOS pump as the rubber in it will crap out quickly.
Really might be a good time to order a rebuild kit, take the carb apart and soak it, clean all the passages etc... You already found one issue with parts installed wrong. Who knows what the po did to the carb. You can just disassemble and clean without a new kit, order one if you think it needs it. I vote for a new stock pump or a inline reg for electric.
Does it have an automatic choke? Does it work and is it adjusted properly? Is the choke valve fully opened after 5 to 10 minutes of running?
on a stock motor I wouldnt think gph would be an issue especially if you got a regulator on it. If you were running a race motor I might be worried about gph. you are far from that requirement.
BEFORE replacing or rebuilding parts you currently have, testing is in order! (1) mentioned by Terrible80 - check the function of the accelerator pump (2) mentioned by ClayMart - check the function of the automatic choke (3) check the function of the distributor advance. (4) if the po changed to a pertronix, did the po also upgrade to an alternator? The Rochester 4GC from 1952 is a decent carb; Rochester did improve them about 1955, but the 1952 version should work well for you. Biggest issue with the 1952 is the stalling on very hard left? turns. And there is a factory fix. Based on your post, if items (1) and (2) above check OK, I think you have ignition problems. One other belated thought: since you did find issues with the floats, you might also check to make certain the primary and secondary jets were not interchanged. Jon.
Thanks everyone! Myself and a few local car buddies (who are MUCH more well versed and been doing this stuff forever) are going to work on this in the AM. I will report back with our findings. These are the kind of guys that if they can't solve it - your best bet is to light it on fire and walk away
Ended up putting on a fuel regulator, and ran it at 3.75 PSI, and I was actually able to get it around the block, and run it through all the gears! Still a slight bog if you NAIL it, but it is also clearly running on 7 cylinders, so that isn't helping. The other thing is when you manually hit the accelerator pump, it is more of a seep, and not a big shot of fuel, so I am looking to probably replace that, but going to see how news plugs and a few degrees of advance work. Also took a sniff of the oil, and it is VERY gassy, so it was clearly getting flooded. So that will get changed in the next couple days. Thanks for your help guys!
Why change to an alternator if you install pertronix?? Just curious as I am having issues also, although a little different than this post Sent from my SM-N950U using The H.A.M.B. mobile app
Russell - are you old enough to remember the television screen picture narrowing when the refrigerator kicked on? Electronics like a stable voltage. Generators do not deliver a really stable voltage below a certain RPM. Alternators do. Jon.
A year old post... makes me wonder if it ever got resolved or the OP gave up on it. I'm not huge on electronic fuel pumps on old cars, sort of a crutch as millions worked well with a mechanical fuel pump. The carburetor needs to be gone through from A to Z, one of those things you should need to do once.
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