I have sent this to the Studebaker forum and have tried many of their ideas, I am trying a fresh approach. I have a 51 Studebaker Starlight Coupe with an original 232 V8. I recently replaced the fuel pump because the seal was bad and it was leaking. I replaced it with a rebuilt NOS pump. It has 5lbs pressure, which is correct and I have a backup electric pump that makes 4 /2 lbs. Need 3-5 lbs to work correctly. The car starts right up and idles great at 600rpm, like it should. Problem is is spits and stutters, even backfires when taking off, under load. Timing, lash, fuel pressure are all correct. Took the top of carb off and cleaned all the passages incase something got lodged in the needle. Carb has been rebuilt. Car will cruise smoothly at 70mph without stutter. It even backfired taking off and killed the engine. I checked the dwell and it does not change when idle is revved up to 3000rpm. Idle increase does not stutter. Car did not do this before the pump was replaced. I will in the next day or so reinstall the old pump if I cannot find a solution. Other ideas bounced around was vacuum leak. Only one line running from carb to advance. Maybe vacuum advance is not working? However I hooked up a vacuum pump to the line that goes to distributor and the breaker plate and it moved back and forth. New gas and tank was sealed. New fuel filter. Looking for more ideas I can check.
Sounds like it could be the acceleration pump. Will it build up speed if you press the accelerator very slowly but gag out if you floor it? Look down the carburetor and work the throttle, you should see 2 jets of gas squirt into the carb throats, if not the pump is not working.
Is there a filter between the fuel pump and carburetor? If so clean or replace it...if not check the fuel line from pump to carburetor THOROUGHLY and check the passage into the needle and seat as well as the needle and seat...if the fuel pump diaphragm was disintegrating debris could have caused a blockage...
The accelerator pump is working. When I pull the throttle rods I get two steady streams. It stutters when floored or a slow build up when under load. Thought of the debris. Filter is before the pump. I cleaned the needle area out. Does not mean it is not plugged again. I know I was getting a steady 5lbs going into the carb. It run better before swapping fuel pumps. Yet that does not make sense to me.
5 lbs is a lot, you only need 2 lbs at the carb. Wonder if the new pump plus the electric pump is flooding the carb? The other possibility is weak spark under load. Look for frayed or broken wire inside distributor, weak condenser or coil, bad plug wires.
The Studebaker Manual has recommended pressure at 3-5 lbs. I only run the electric to help start it and when it goes into vapor lock. I failed to test the original pump pressure before I took it off. Hence why I may swap it back to see if it is the new pump. The ignition electrical is the next thing to pursue. I will be checking the coil today. At one point the breaker points plate was stuck and would not adjust freely. I did free that up and lubed it again. Is there a test to check for weak condenser? Would a vacuum leak from the carb to the vacuum pot cause this. Bad vacuum pot cause this? The original vacuum line from the carb to the vacuum pot is a brake line connections. Maybe a different setup would help? It is just that it idles so well and runs at 70mph on the freeway no problem.
go back to the carburetor - float sticking - needle / seat not correct/dirty? - makes no sense to have an electric & manual fuel pump - run one or the other - if you run electric use a pressure regulator - yes, too much fuel pressure will cause problems - one other possibility is the gas tank fuel pick up tube - have a "sock" on it ? clogged/bent? tube too close to bottom of tank?
Check the plug wires with a tester. My Hawk started doing that, and no amount of tuning, adjusting etc would make that go away. One day I found the prob to be a good looking coil wire that had been arcing internally at a broken conductor and slowly chewing an inch long gap in the conductor inside the insulation where it couldnt be seen. The spark seemed fine when quick-checked, but was weak enough to get snuffed out when the combustion chamber pressures rose with heavier throttle. A new coil wire gave the engine a whole lot more power. I had a 50 Starlight Coupe bulletnose once that started acting like that. It was one of the 6v ignition wires that started getting loose at one of the overdrive switches' terminals but still looked properly fastened. The overdrive is wired in a manner that a switch will kill the ign only for a very short instant to put a bit of slack in the gears when a certain shift is made, then power comes back on. It's supposed to be quick enough not to notice.... until the switch acts up. P.S. Once when towing a trailer cross country I had one v8 slowly losing power. Since I had just replaced a timing chain set on one of my other cars, and this started acting the same, I stopped at a shop and asked how much would it cost if this wagon needed a timing chain. The guy quickly re-set the points I had tuned up just a couple weeks earlier and told me the rubbing block had worn down a bit and simply needed resetting. $10 I just recently fixed a friends 52 Pontiac straight eight that was acting similar to yours. The prob I traced down with his was that his points were getting intermittent contact thru the rivets that connected the points wire connector to the flat points spring, to where the riveted flat spring connected to the actual points-arm. Squeezing the rivets at both ends of the flat ribbon points-spring restored proper connections. It was an easy starting easy driving Pontiac after that. I would also double check how your pumps plumbing is arranged. It is possible you could be encountering an empty carburetor bowl at the wrong moments. WHY BE ORDINARY ?
What - Dare to be Different said.........had a coil wire that looked good....a couple of pulls and it came loose.
After dark start the car open the hood and see if there is a light show going on starring the spark plugs and wires. My 259 had those below Accel wires and had an intermittent stutter at idle and bog while accelerating. All my other tune up parts were new and correctly set. So I checked after dark and there was a mini lightening storm accompanied with stutter. Went to tractor supply got one of their universal v8 wire sets. Some trimming some crimping and some order through the wiring looms, all better. Confirmation of the 90% rule. 90% of all electrical problems are fuel related, and 90% of all fuel issues are electrical!
@lelshaddai, I just went through this with a 1955 Studebaker. It is likely the distributor wiring. If you look at your Delco distributor, there is a nutted post or junction block on its side. The hot wire from the coil attaches there. From there, there is another separate wire that goes to the points. That wire is likely the cause of your problem. I would recommend cutting back the wire from the main harness to the coil and install a new crimp eyelet. Make two new pigtails to replace the other two wires. This should solve your problem. I have been trying to locate a picture of this set-up but I have been unsuccessful. If I think of it when I get home I will snap a pic for you.
Here is a picture of the insides of your Delco distributor. You can see how it is set up and the wires you need to replace.
You also can't replace the brown wire with stuff off a spool. That wire flexes with the movement of the breaker plate as the timing advances and retards. Needed to be flexible enough to deal with the movement and strong enough to deal with all the flexing .I believe you can still get the right stuff from Napa if the counter guy knows what a distributor is...
I did not know that. That is good information and it makes sense, Those wires are rather limp when you remove them. Unfortunately it is too late for me. I made a lead from vinyl insulated wire, crimp connectors and shrink wrap. It has served me well so far. in the future if I ever have to do this again, I will look for the right wire.
One other note your breaker cam looks dry. That small piece of red felt is supposed to carry oil to the cam to keep the Blu rubbing block from wearing too quicky. A few drops of light oil, 3 in 1 or similar needs to go on that to do the job.
If you suspect an ignition issue,hook up a timing light and stick it under a windshield wiper arm and take a ride...observe the pattern of flashing, at several thousand rpm it will look like a flashlight, when the engine starts to perform poorly if the timing light pattern changes you will KNOW it's ignition related and not be speculating. Also if you have a manual choke when the engine starts performing poorly pull out the choke some, if some choke makes some improvement you have a fuel delivery ( pump, filter etc.) issue or a mixture issue ( pluged jets, passages etc) . One other thing I have seen is double wall exhaust pipes with the inner pipe collapsed causing a major exhaust restriction ( this will show up as low vacuum if you hook a gauge to manifold vacuum.)
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