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1947 electrical fuel pump question

Started by Rob, February 18, 2007, 07:39:01 PM

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Rob

My 1947 cadillac mechanical pump is percolating when the engine is hot. Looking at the glass dome I can see a lot of bubbles coming up from one side (the side facing the engine center). I did try to isolate a portion of the incoming fuel line but no improvements.
Due to those bubbles the car has some hesitations when I keep the gas pedal lightly and drive at normal temperature. No issues fine when I fully depress the gas pedal.

I have a 6v electric pump I bought form Coopers-vintage in the past, which I could mount. My question is: should I remove/bypass the vacuum mechanical pump completely and reroute the lines directly to the carburator or is there a better way ?

Thanks
Rob Brandys
47@bigcadillac.com

Ralph Hoyt

Rob,

I mounted my fuel pump and tied it to a switch I placed under the dash.   Normally I use only the manual fuel pump, but the moment i have any hesitation or vapor lock, I flip the switch and off i go.  I usually only run it for a minute or so and flip it back off.  

not sure I helped or answered your question, but fuel for thought.

thanks,

Ralph

Rob

any reasons for keeping the mechnical pump then?
.rob

Bill Ingler CLC 7799

Hi Rob- What you have going on with your 47 is vapor lock. What I would do before making any major decisions on a fix is find out what others have written on this subjet. At the top right of this page you will the word search. Click that once and then you will see Words to search for. Then type in Vapor lock and you will get about 82 postings on the topic.

Dennis

I replaced the defective mechanical fuel pump with another (remanufactured) mechanical fuel pump on my 57 Eldo Seville many years ago.  Well, about a week afterwards, the car kept acting like it was out gas and hesitating, etc.  Same thing, bubbles in the filter.  I pulled the pump off and dissasembled it.  I found that neither of the two check valves were properly installed.  They were in place, in the right orientation, but the boss that they sat in was not properly crimped down. (A leaky heart valve will kill a human as well)   A few whacks with a hammer and punch and the check valves were seated firm.  Reinstalled it and that pump is still going strong.

Unless you want to install an electric fuel pump for S&Gs, Id recomment a little further snooping to see if you can get the mechanical one beating smoothly again.

JM2C,

Dennis

Rob

Dennis, thanks for your answer.
I could imagine that my fuel pump has worn out and is leaking air, hence the bubbles. besides the car has no troubles with idling or running under load or even steep hills as long as I fully depress the gas pedal. the pump seems to be able to bring enough fuel for that. not sure if this is even really a vapor lock issue.
But the air bubbles and hesitations only appear when hot.
I will try to rebuild the fuel pump then.
Rob

John Washburn

Rob,

If the car hesitates as you say, with all the other elements listed as good, I dont believe the hesitation is the fuel pump. You might check the accelator pump or the electrical system.

Second if you see bubbles in the gas it might mean the gas lines are leaking or the fittings are leaking. Check this out also, or when you rebuild the fuel pump and add a electric fuel pump you might still have the bubbles. Bubbles - they help create vapor lock.

Good Luck

John Washburn
CLC #1067

Rob

John, thanks a lot for your answer.
The hesitations appear only when I hold the gas pedal steady at constant speed, accelertor pump is not engaged. No hesitations on acceleration. No issue at cold (first 10 minutes of driving).

I did recheck and tighten the rubber hose but those bubbles keep coming up for a few minutes after the engine has been shut hot, so that would eliminate the air leak as cause. I dont get bubbles when cold.

I will replace the fuel line from the gas tank to the pump, as it is old and pinched at places, this could contribute to lower the pressure and gasoline boiling point.
Id like to solve this issue wihtout adding an electrical pump if possible.
My other car, a 1948 Buick never had any issues even on very hot days, city traffic driving.
By the way I dont use any ethanol mix in those cars.
I will redo the ignition timing. perhaps this is again ignition related but if then, the issue should persist even at cold engine.


Rob
47@bigcadillac.com