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Stalling 1938 Studebaker? Any ideas?


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The 38 started stalling as I accelerate. Starts great, idles very smoothly, first gear starts off find them at about 10 miles an hour starts bogging down. I replaced points, rotor, condenser, distributor cap, coil, electric fuel pump, fuel filter, did a compression test - 90 on 1,3-6 and 86 on 2. Bypassed the mechanical fuel pump and still no change. I’ve put 7000 miles on it over the last four years and it’s always run great. The only thing I can think of is the carburetor. Took that apart today and the single barrel stromberg seems clean, appears the accelerator pump is pushing fuel. I have not reinstalled it as it is soaking in cleaner fluid overnight before it goes back in the car. Could it be as easy as a dirty carb?  
When we rebuilt it five years ago we cleaned and lined the gas tank and the old fuel filter seemed clean and the glass bowl on the mechanical is clean. The inline filter never seems to fill completely, it looks less than half filled at all times. Not sure if that is ok or a problem.
Any help to get it back on the road as it is my daily driver will be appreciated. 
Thanks

dave s 

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Dirt is the killer of all carbs. Pinhole leaks in fuel lines, or weak collapsing rubber fuel hose pinching off full pressure supply? If the bowl isn't filling that shows a lack of supply or lack of pump pressure.

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Run it off a remote fuel tank fopr test. I've had the selaer come loose off the insides of a "sealed' tank and plug up fuel pickup tube. Also-a faulty condensor can drive you crazy.

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I had a similar situation with my '49 Studebaker, I wound up rebuilding the fuel pump, clean out the fuel lines, and tank, and she was fine after that.

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Posted (edited)

Ed, never thought of a week rubber line. Will check that out. 
Terry, checked the gas cap and did not have any back pressure (sucking sound) when I opened it. It’s not a pressure tank.
Bull run, thought of the condenser but it fires right up and runs smoothly at an idle. I’ll try the external tank if the carb rebuild doesn’t work. I’m alone so not easy to set it up safely. The filter and glass bowl don’t show and debris but they could be so small these old eyes can’t see them. 
John S, I bypassed the mechanical and just used the electric pump then tried a new electric and still no luck. But you may have triggered a thought. If the mechanical diaphragm is bad it could be sending gas the the crankcase. When I bypassed it I did not plug the in/out ports could that possibly have caused the problem?  I ask as I have no clue on electrical or fuel problems with a car.  
I thank you all and hope you will let me know if you can think of anything else or correct my thinking in any way I may be off base. 
Thanks

dave s 

Edited by SC38DLS (see edit history)
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15 minutes ago, SC38DLS said:

Ed, never thought of a week rubber line. Will check that out. 

Don't forget the flexible line that provides the input to the mechanical pump.

 

While your carb is apart, if you have a leather seal on your accelerator pump, soak the plunger-with-seal in castor oil from the drugstore for 24-48 hours.

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"thought of the condenser but it fires right up and runs smoothly at an idle. "

The condenser could still be the problem - they falter under heat, load and/or rpm. One of the easiest things to replace... 

 

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Thanks Grimy. I don’t remember if it’s leather but will check. There are actually 4 places of rubber lines, at electrical pump, mechanical pump, before the carb and at the inline filter. I’ll check or replace all of them. 

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Vermontboy I’ll change it out. I had no idea they could cause a problem under load or rpm if they were working ok to start. Biggest problem is getting a good one from China. I’ve had new ones that were bad out of the box. 
thanks 
dave s 

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TerryB. My last hope as the carb rebuild did no improvement. Studebaker has an automatic vac spark advance that is at zero at idle and up to 12 degrees on fly wheel under full throttle and load. I’m trying to figure out if the distributor moves or just the internal part. I can’t currently move any part of it so this may just be the problem. 
I think I owe all responded a frosty cold one if I ever get it running again. 
dave s 

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Make sure that advance works and doesn't leak vacuum at all. If it turns out that only the breaker plate moves, and not the whole distributor, look for a ground wire from the breaker plate to the distributor housing, make sure it hasn't broken. If the whole distributor moves, there should probably be a ground to the block. Whatever the points and condenser are bolted to have to have a solid ground back to the block.

 

You could also try a slightly wider than recommended points gap. If the distributor bushings are worn out, that might make a big difference. Recheck the timing if you try it, because widening the gap advances the timing, and that could fool you into thinking it made a big difference.

 

The symptom sounds like a blocked gas line or some fuel delivery problem to me. Try it with no gas cap. If that doesn't help, run it on a boat can or something. Alternatively, if the suction (tank) side of the mechanical fuel pump is fed from the line with a rubber hose, you could tee a vacuum gauge in there and tape it to the windshield. If the fuel line is blocked, the vacuum will go real high about when it starts to cut out.

 

If the connection from the line to the tank in the back is a rubber hose (probably not in a car that old), a pinhole in the rubber could do it. It could keep the fuel pump from doing it's job but wouldn't leak enough gas to notice.

 

Edited by Bloo (see edit history)
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Bloo thanks. I’ll have to check a couple of things to be sure I fully understand all you mean. I don’t think the fuel line is having any problems but will try your ideas. I know this may be wrong to think the way I am but I can’t figure out any error in my thinking. It starts so easily and runs so smooth at an idle it doesn’t seem it should be fuel or electrical (points, condenser, cap, coil) take it out and at about ten miles an hour it starts to bog down. No power and sounds like it is really straining. It’s been a great running car since rebuild four/five years and 7000 miles ago. For it to suddenly start doing this I’m baffled. That may be just because I’m old and have forgotten some important aspect of the process but that’s life. 
thanks

dave s 

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Fuel starvation under load, could it be crud in the fuel tank? A crack in the carb float? I too have seen the rubber hoses fail a few times,  and the fuel pump is sucking in air along with the fuel. Under load the demand for fuel is much greater. I feel if the points were that bad it would not even start. 

Edited by John348 (see edit history)
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John348. Rebuilt the carb, new inline filter and glass bowl clean. Checked the rubber hoses none seem to be collapsing or leaking/cracks. New plugs, points, rotor, condenser, cap, coil and electric fuel pump. Compression is 90 on 1, 3-6 and 2 has 86. Only part I can think of is vacuum for distributor spark advance and I’ve ordered the part. I’ll check timing tomorrow as old injuries from football and army (disabled vet) only allow me a few hours a day working on it. It’s my daily driver and has run great since total rebuild five years and 7000 miles ago. I really need to get it back on the road as my riding buddies miss their daily ride !  

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There could be a problem with the pick-up tube in the tank getting clogged and releasing as soon as the demand for fuel and momentum. Does it happen if you give it throttle when parked? 

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Posted (edited)

Yes it does somewhat. Not a great description but I’m not sure how to say it. When moving its easy to tell it bogs down. Sitting still the engine sounds like it’s running rougher but as not bad as when under load. Does that make sense? 

Edited by SC38DLS (see edit history)
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One more thing I watched the clear fuel filter and it seems to always be half full. Doesn’t go lower or higher when I give it gas or let it idle. 

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Have everything except the fuel pressure when it happens. Never had a Stude but other carbs with small float bowls were notorious for emptying before through the 1/4 and would just bog. Idle a few minutes and would be OK again.

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Posted (edited)

Padgett it pushes gas fine as far as I can tell. 
John I agree but I think it’s the vacuum spark advance module connected to the distributor. It is supposed to advance the spark as much as 12 degrees under full acceleration or load. I don’t think it is moving at all. I’ll check tomorrow if I can figure out how to do that. 
Thanks guys 

dave s 

Edited by SC38DLS (see edit history)
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12 hours ago, SC38DLS said:

take it out and at about ten miles an hour it starts to bog down. No power and sounds like it is really straining.

 

That is *THE* primary symptom of a fuel delivery problem. I am not saying that is what the problem is for sure, but with a symptom like that it is a very good possibility. You can look at the sediment bowl but it won't tell you anything. It boils down to the fact that the car burns more gas when you are underway. The fuel system has to be able to supply enough volume, or it will just run fine until you put a load on it and then go lean and refuse. There could be many different reasons, plugged vent, plugged line, fuel pump not getting enough stroke, etc.

 

Now some of the things I suggested and why.

 

Removing the gas cap. If this fixes it, the fuel pump was creating vacuum in the tank and eventually couldn't suck hard enough to get any more gas. The vent is plugged. It might be vented in the cap, or it might be somewhere else, depending on the car, but the vent is plugged.

 

Fuel line sucking air. It is easier to suck air than gas, and sucking gas through that little gas line is harder than you think. If there is a rubber hose at the back I would just replace it, and make sure it seals on the pipe. While it is off, I would disconnect the other end of the steel line and blow the line out (just because) and also I would cap one end of the steel line running to the front, and suck on the other end with a mityvac. It should not leak down. If it passes this test, there is no pinhole in the steel fuel line. Surprisingly, fuel almost never runs out on the ground when there is a pinhole in a hose or hard line on the suction side, even with the car shut off.

 

Line restricted: This could be a plugged pickup in the tank or an internally collapsed rubber hose somewhere. A vacuum gauge teed into the line at the front on the suction side will go sky high as the pump tried to bring more fuel and cannot move any. This happens with a plugged vent too, but if removing the cap didn't help and the vacuum gauge still goes way up suddenly a little before the problem occurs, the line is restricted. Maybe at the fuel pickup if the hard line blew out ok.

 

Now about that vacuum advance. I would check that out thoroughly first because it's easier. It advances under part throttle and then goes back away under full throttle. There is no vacuum under full throttle to pull on it because the throttle is open. Advance for full power is handled by the centrifugal weights. If the vacuum advance is leaky, it will not advance at part throttle, and that causes a bog. It also will leak vacuum, leaning out the mixture a little. That might make it worse.

 

If the vacuum advance does work, it will move either the breaker plate or the whole distributor. The points must be solidly grounded or the ignition wont continue to work right when the vacuum advance moves. If you have a movable breaker plate, there is most likely a ground wire from the plate to the distributor case, so the vacuum advance cannot interrupt the ground as it moves the plate. If the whole distributor moves, there could be a wire from the distributor to the block for the same reason. the wires take constant motion and can break. If the wire has insulation, you might not see it.

 

Good luck and let us know what you find.

 

 

 

Edited by Bloo (see edit history)
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Wow. I really appreciate the time for this explanation, now I have o be sure I understand it all. I think it all makes sense. It will take me some time to check it all out (braces on legs makes it hard to get around and under car plus limits time the back can bend over to work) but I will let you know how it goes. There are 4 or 5 places rubber hoses were used in the gas line. I will replace them after doing your suggested test. 
I did switch out the electric fuel pump (as I carry a spare) with no change in running condition. Also bypassed the mechanical with no change so maybe it is a plugged pickup or bad line. 
I will post as I check things out. 
Thanks for all the help it is appreciated. 
dave s 

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Hi all - I tried some of  Bloo’s suggestions 

Removing gas cap does nothing. 
Watched the vacuum advance as I gave it gas - absolutely did not move. 
 

Per that result I am trying to see if I have a vacuum leak. I don’t have a vacuum gauge so may just go get one when I get rubber gas line. 
 

Going to replace all rubber lines for fuel and vacuum just to be on safe side. 
 

I will check the tank when I replace lines. I assume (maybe wrong but how else can I check) if it runs out free it’s not a blocked gravity feed port. 
 

I will let you all know results as I go. 
Thanks for your knowledge, patience and putting up with my lack of knowledge. 
dave s 

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Just tried manually moving vacuum advance at distributor while giving it gas. I was able to move it (distributor moves with it not just plates inside so easy to see) and it sounded like it ran better. Hard to really tell but I’m hopeful. I’ll get the vacuum gage, hoses and replace them. I also found a vacuum module (if that is what it typically is called) that will be here Tuesday or Wednesday at the latest. 
I’ll let you know results. 
dave s 

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Vacuum diaphragm!  Grey hair is pulling memory cells right out of my head. Not sure if having hair or better memory at this age is the way to go! 

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Dave. I would suggest pulling the feed off the vacuum advance from the carb or the intake. sealing that opening so there is no vacuum leak, and see if the stumble goes away. If the rubber diaphragm is ruptured you are just sucking in air, leaning out your mixture when it is needed the most 

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You could try pulling a vacuum in your vacuum advance with a hand vacuum pump with the engine stopped while watching for the plate in the distributor to move. If you don't have a hand vac pump, lung power will do the test as well.

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Got the fuel line hose and vacuum hoses also picked up a vacuum gage. Replaced the lines and still same results. Checked the vacuum from carb to distributor down at the distributor end an at an idle it is 15 goes up as I accelerate. Hooked it back up to distributor and does not move it at all. Distributor can be moved easily by hand. So I think the vacuum module/diaphragm is bad. Have one on order so will install and let you know results.  
dave s 

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Got the new diaphragm for the advance on the distributor and still have the same stalling. I will check the vacuum numbers again tomorrow. I’m out of guesses on what could be wrong. Very frustrating 

dave s 

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Points, plugs, condenser, rotor, cap, fuel filter, electronic fuel pump, coil, vacuum advance diaphragm at distributor, rebuilt the carb, replaced all rubber fuel lines and vacuum lines. What else can it be?  Timing ?  
 

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Tee in the vacuum gauge on the suction side of your fuel pump, tape it to your windshield and try to drive. The needle is going to kick all over the place while the mechanical pump is pumping, and then settle down while the carb is full, and then start kicking again, etc. in normal operation. What it should not do is suck up and hold a good vacuum. If it does, the fuel line or fuel pickup is restricted.

 

Edited by Bloo (see edit history)
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Sorry I just saw this. Don’t know how I missed it. Making too many changes so quickly is seldom productive. Timing never changes while a car has been sitting. Carburetors don’t go out of adjustment when sitting. Usually only three thing can go wrong while a car sits over the winter months. Bad coil, bad condenser, or a plugged carb. You need to isolate the issue. Knowing if a running problem is spark or fuel is a skill only developed over time......and a lot of experience. Stop what your doing, develop a diagnostic routine, and follow it. It’s possible all the changes have added problems to the initial issue. What you describe, and assuming all the the parts changing you have done are correct, I would look at the coil first. Also check battery voltage, check the battery.....sometimes a bad battery can cause issues. Look for voltage drop at the coil. Load test the coil. Bad ignition switch is a possibility also. Basically you need to prove the entire system from top to bottom. It’s hard to get a reading on a car from other peoples descriptions. While I know your frustrated, it should be a simple fix. Does the motor break down just standing still rolling the throttle up? If yes, add propane from a remote source and test......that will tell you if it’s starving for fuel. Things like lean burn misfire can be hard to diagnose without proper tools and experience. PM me you phone number, it’s easier to help over the phone. I have a doctors appointment Thursday, and can call you after lunch. I expect we can sort it out over the phone quickly. Best, Ed.

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Thanks guys. Bloo I am going to check vacuum again too be sure I know what readings are and will see if I can do your test. Ed, that is most kind of you. I hate to take up your time as I know how busy you are at the shop and with the great white in your spare time. Saying that I am out of ideas so will PM you. If it’s not today anytime you can call is fine. 
Thanks to all of you for the help it is appreciated. 
dave s 

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On 3/12/2021 at 5:44 PM, SC38DLS said:

take it out and at about ten miles an hour it starts to bog down. No power and sounds like it is really straining.

 

It happens this way EVERY time? Starts great, idles great, just won't develop any power after a short time? 

 

Drop exhaust pipe from manifold. If safe, drive it that way to test. Might not be safe, maybe just drop muffler off. I know, rusty fasteners make any part of this test hard to do!🥵

 

Partially clogged exhaust system makes this low power issue*. Completely clogged systems make it not run, not even start in most cases! The old potato in the exhaust pipe trick...😆

 

* extremely common on GM systems of the 70s, a double wall exhaust pipe collapses internally with NO external noticeable distortion. Have to drop pipe off to test run.

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Perhaps an easier way to check for plugged exhaust:  With warmed up engine, attach a vacuum gauge.  Have a helper hold the throttle/accelerator at 1500-1800 rpm (car at rest) for two full minutes.  It will take 15-20 seconds for the gauge to stabilize after throttle is applied.  Note initial stabilized gauge reading.  If reading drops, and continues to drop, over the balance of the two minutes, THEN it's worth your time and discomfort to drop the exhaust.

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Thanks guys, I will check it out today. Frank your description is correct. 
Trying a couple of things on the  electric side before I drop the exhaust pipe. 
I will let you all know results. 
I do appreciate the suggestions and help. 
dave s 

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  • Peter Gariepy changed the title to Stalling 1938 Studebaker? Any ideas?

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