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'50 Ford carb leaks fuel after shut down...when "hot"


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When "hot", run the car, shut it down.  

 

~5 minutes later, fuel starts running from the main discharge nozzle, puddles on the throttle blades and runs out the throttle shaft, leaking onto the intake.  
Recent fuel pump, 

Car runs good when running

Checked for needle and seat sealing; it seals good. 

 

I watched it happen today, engine was 205* F when shut off.   What gives? 

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Fuel bowl vent may be clogged thus driving fuel out the main discharge  tube as it heats, bubbles, and expands during a hot soak ? 

 

Have you checked the float level ? It may be too high and as the fuel inside the carb boils, it gets pushed up the main discharge tube by gas vapor bubbles.

 

Paul

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56 minutes ago, carbking said:

Check this link to the troubleshooting section of my website:

 

Fuel leak at throttle shaft when hot

 

Jon

Thanks.  That precisely confirmed my hypothesis.   In fact, last night as the carb was overflowing in the bores, I loosened the fuel line between the carb and fuel pump; got a squirt of fuel and a "Shuuush" of air. 

 

Thanks for the link.  Bummer about the problem.   The thing needs an "accumulator" in the fuel line to manage that pressure for a few minutes.  Or something. :(

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Carbking, 

 

If you see this, I installed a Summit Racing adjustable FPR in line between the pump and the carb, and set it deliberately low at 1.5 PSI.   Just barely enough, in my estimation, to get gas into the float bowl.  My hope was that it would maintain the 1.5 PSI after shut down between the regulator and the carb.  It tried to, but pressure still crept up to ~3.5 PSI for some reason.  IDK why...maybe it's just too much pressure once it boils the fuel in  the pump for the regulator to hold it?  Anyway, same results after a hard climb and shut down; carb overflowed into the intake. 

 

Has anyone tried using the return style fuel filter, and letting that return go back to "tank"?  A filter like this:

 

 gf423.jpg

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The pressure build-up is due to expansion of fuel in the fuel line between the regulator and the carburetor.

 

I have been suggesting the use of the return line for 30 years. I didn't invent the idea, just looked at what the manufacturers did 50 plus years ago on vehicles with big engines and air conditioning. The factory engineers were not dummies. Often a good idea to see how they solved a problem, and see if their solution may be migrated to a similar problem.

 

Jon.

 

 

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Copy that.  If the 1.5 PSI set pressure doesn't allow enough "head room" for expansion between the regulator and the carb, then I'll install a filter with a return, like the one shown above, and plumb it back to tank.  Thanks for reading and sharing your thought.  👍

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21 hours ago, carbking said:

The pressure build-up is due to expansion of fuel in the fuel line between the regulator and the carburetor.

 

I have been suggesting the use of the return line for 30 years. I didn't invent the idea, just looked at what the manufacturers did 50 plus years ago on vehicles with big engines and air conditioning. The factory engineers were not dummies. Often a good idea to see how they solved a problem, and see if their solution may be migrated to a similar problem.

 

Jon.

 

 

 Not just the big engines, either. Had a 71 Toyota Corolla with the 1600cc engine and no A/C, that had a return line at the carb inlet.

 

Paul

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Posted (edited)

Update:  The thing flooded again, this time with only ~1.9 PSI showing in the fuel line between the regulator, and the carb.  Less than 2 PSI.    I have a hard time believing that 1.9 pounds is pushing past the needle and seat. 

 

15144[1].jpeg

 

 

15128[1].jpeg

 

 

Now I wonder if it's boiling in the carb, the volume created by bubbles is displacing fuel enough to raise the level and cause fuel to run out the discharge nozzles?  The next test that I'll run will be to run it hard, then pull it in the shop and quick, hurry up and pull the top of the carb off and flip it upside down, before the symptom typically starts (usually takes about 3-5 minutes).  Then watch; fuel will either boil/rise in the bowl...or start pushing through the upside down, float/needle/seat.   I'll be able to see, which is the issue.  I hope.

 

 

.

Edited by Tom400CFI (see edit history)
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If you want to see if it's fuel line pressure pushing past the float needle, as soon as you shut it down for a hot soak, break the fuel line connection at the carb. That will eliminate all fuel line pressure. If it's still pushing gas out onto the throttle plates then it's boiling in the carb that is causing it.

 

Have you checked  the float level ? 

 

Paul

Edited by PFitz (see edit history)
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Yep, that method would work too.  Good advice.  Thanks.

 

I have not confirmed the float level....I don't know the spec or measuring points for this carb.

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If that's the original type carb, asking the Ford guys down below in the Ford forum, some of them would likely have a manual and be able to tell you what you need to know to check float level on that year Ford.

 

And if you know anyone who has a Motors Manual covering Fords that year, in there, too.

 

Paul

Edited by PFitz (see edit history)
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