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fuel drainback issues

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Old Jun 16, 2025 | 07:11 AM
  #1  
mattking's Avatar
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From: Rosemark, TN
fuel drainback issues

Guys,

I'm having a recurring issue with my wife's Studebaker. This has always happened to some degree but it is getting worse and worse. The carb gets empty after even a week of not running, and it is getting harder and harder to get it started. Once running there are no issues. It will start easily the rest of the day or even the next day and drives well. It has a bowl style filter that I think her grandfather added. That was leaking and I bypassed it with a inline filter to get her driving for the weekend. We always use non-ethenaol gas. The tank has been boiled out and lined, there is all new rubber fuel hose and the original steel lines. The mechanical fuel pump is new-ish I think I put it on 7 years ago, or about 3000 miles ago. We just recently rebuilt the Stromberg WW carb.(I am having a problem w the automatic choke closing, but i think that is unrelated)

Anyone have experience with similar issues or any ideas? I've thought about putting a clacker fuel pump in and running it just to prime everything up, but I'm unsure how to plumb it in...ie would the mechanical fuel pump pull through it with the electric turned off.... I don't know I'm out of ideas
Old Jun 16, 2025 | 07:43 AM
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As a casual observer, it seems as though the problem started with the inline filter, or am I imagining that?
Old Jun 16, 2025 | 07:50 AM
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Originally Posted by fleming442
As a casual observer, it seems as though the problem started with the inline filter, or am I imagining that?
I believe you are correct there It certainly got worse maybe two or three weeks after I made that change. I gave up this weekend trying to get it cranked, as I was worried about overheating the starter and draining the battery. I mean its all original and honestly very basic. Ill look at it this afternoon.

edit: I should say it was sediment trap fuel bowl and did not have a filter in it, like some do.

Last edited by mattking; Jun 16, 2025 at 08:06 AM.
Old Jun 16, 2025 | 08:54 AM
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I have many issues with this after the car sits and not starting for a while. I assume if you prime the carburetor it fires right up ?? If you are not smelling any external fuel leak after it sits, the problem is either the float bowl is leaking down fuel into the engine or the fuel is evaporating. In real hot weather the fuel will evaporate very fast...I really do not see how a inline fuel filter would cause such a problem, even if the line created a vacuum pull, [highly unusual] the needle & seat would stop the drain off .

Last edited by zl1 camaro; Jun 16, 2025 at 09:05 AM.
Old Jun 16, 2025 | 08:56 AM
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Are there sections of rubber in the fuel supply line that can be pinched closed to test the drawback theory? A failed fuel pump ca allow gasoline to enter the crankcase, smell the oil dipstick for gasoline contamination.
Old Jun 16, 2025 | 09:12 AM
  #6  
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From: Rosemark, TN
Originally Posted by zl1 camaro
I have many issues with this after the car sits and not starting for a while. I assume if you prime the carburetor it fires right up ?? If you are not smelling any external fuel leak after it sits, the problem is either the float bowl is leaking down fuel into the engine or the fuel is evaporating. In real hot weather the fuel will evaporate very fast...
Yes if I prime it it fires right up. You're thinking it could leak from the carb into the intake?

Originally Posted by Sugar Bear
Are there sections of rubber in the fuel supply line that can be pinched closed to test the drawback theory? A failed fuel pump ca allow gasoline to enter the crankcase, smell the oil dipstick for gasoline contamination.
Are you saying the the pump could leak directly into the crankcase through it's mounting hole? I will check the oil for fuel smell tonight. It only gets changed once a year or so. She takes it on a drive on weekends when the weather is nice so it really gets no miles on it.

The main steel fuel line transitions to a rubber piece into the filter and the filter to the pump but then it is steel line front the pump all the way to the carb. Once i get it running and fuel again I could pinch this closed and see what happens
Old Jun 16, 2025 | 09:21 AM
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Yes, a leaking pump can allow raw gasoline into the crankcase through its mounting to the block. Two telltales are gasoline in the oil and an overly clean area of the pump on the inside of its mounting area due to it being washed by gasoline.
Old Jun 16, 2025 | 10:05 AM
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From: ROCHESTER NY
Originally Posted by mattking
Yes if I prime it it fires right up. You're thinking it could leak from the carb into the intake?


Are you saying the the pump could leak directly into the crankcase through it's mounting hole? I will check the oil for fuel smell tonight. It only gets changed once a year or so. She takes it on a drive on weekends when the weather is nice so it really gets no miles on it.

The main steel fuel line transitions to a rubber piece into the filter and the filter to the pump but then it is steel line front the pump all the way to the carb. Once i get it running and fuel again I could pinch this closed and see what happens
The float bowl could be porous, not a mounting hole. Either take the carb off and or or just remove the air horn & fill the float bowl with fuel & see what happens. this should hold fuel for a long while. If Within 3 or 4 days the float bowl is empty, u found ur problem.. GOOD LUCK

Last edited by zl1 camaro; Jun 16, 2025 at 10:09 AM.
Old Jun 16, 2025 | 10:20 AM
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From: Rosemark, TN
Originally Posted by zl1 camaro
The float bowl could be porous, not a mounting hole. Either take the carb off and or or just remove the air horn & fill the float bowl with fuel & see what happens. this should hold fuel for a long while. If Within 3 or 4 days the float bowl is empty, u found ur problem.. GOOD LUCK
^^Thanks a ton i was thinking about how to test it



All you guys have at least got me motivated, and I needed that.. thanks
Old Jun 17, 2025 | 09:25 AM
  #10  
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From: Rosemark, TN
I definitely have contaminated oil. Its thin and greenish and stinks of gas. I dove into the world of Studebaker fuel pumps, and found out that the Airtex brand pump I bought in 2017 is known to have many issues..Most of them won't work at all when brand new. I had saved the box and put the old carter pump in it and it and found out it can be rebuilt. In addition I dug through all the parts boxes we got with the car and found the original, or original style pump which has a built in glass bowl filter. This is also rebuildable and the route we are going to take.

While I've got it all apart I will check the carb for leakage as well and see if i can figure out why the choke doesn't set.

Thanks for the good info and pointers..


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