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Hard to Start after long lay over


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Hi I am new to this forum.  My 1950 Dodge is in very good to excellent condition and runs very well.  The only problem I have is starting it after a long period of not being started.  In order to start under those conditions I need to pump the accelerator while cranking the engine.  When the car has been started and run recently it starts very well.  I was wondering if the problem could be that the fuel in the float bowl has evaporated and I need to pump gas back into the carburetor first. Also was wondering if adding a glass bowl filter just before the carburetor might help. 

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first, after the next spell of sitting, eliminate the guessing and remove the carburetor top for inspection of fuel bowl contents to be sufficient to pump fuel for a cold start...you are defeating your sissions choke by pumping.  This is a mechanical assisted electrical mechanism....read the start procedures for your vehicle.  

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This is a pbm that most of us have when our antique cars sits for several days without being started.  To help eliminate this issue you can put on a 6 volt positive grounded electric pusher FP back by the gas tank. It needs to be near the gas tank because the electric pumps are a pushing pump and not a  pulling pump like the mechanical pump that is in your car.

 

Also have a toggle switch installed so that you can turn the  electric pump on when you are priming the carb after it has sat for several days.  Let it run about 30 seconds and then try to start the car. This way the fuel has come up through the regular fuelump and into the bowel on the carb and you then can start the car with out grinding the engine and the battery.

 

I have one in my 39 desoto.

 

Rich HArtung

Desoto1939@aol.com

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Agreed, fuel evaporates. You might have a little left in the carb bowl. When you floor the accelerator pedal once, if there is enough fuel left, you might get 1 squirt from the accelerator pump into the carb throat. The engine may fire a couple of times then die. You could also not get any fuel into the cylinders. Depends how much has evaporated from the carb.

 

The mechanical fuel pump has to crank over, pumping fuel from the rear fuel tank, up into the carb bowl again. That can take a while of cranking. This is likely what you are experiencing. Refiling the carb bowl is accomplished by cranking the engine over with the starter. This turns the camshaft, which causes the fuel pump to do the work.  You could install an in-line 6V electric fuel pump. You turn it on for 5-10 seconds, before cranking the engine over. The electric pump will fill the carb bowl quickly. 

 

For further depth if wanted:

The fuel bowl is vented to atmospheric pressure. Fuel can and does, easily evaporate. Especially with all the ethanol in it. When the pistons are cranking, up and down, they are creating vacuum. This vacuum is present and manipulated up in the carb venturi.  A low pressure point, less than atmospheric pressure is present now in the venturi.  This little magical situation draws raw fuel from the carb bowl, via the jets into the venturi.  If the car has not sat for an extended period, there is enough fuel in the bowl to allow this to easily happen.

 

Saying that....You need lots of extra fuel when the engine is stone cold. The reason is, the raw fuel that enters the venturi is vaporized into a very fine mist. Like a heavy fog hanging over a cool swap at dawn, in the fall. When the engine is cold, this misty air/fuel mixture sticks to the intake manifold walls, and intake valve ports.  It condenses and form droplets on the walls. So a lot of the fuel does not make it inside the cylinder to combust.  So we choke the air supply off. Closing it with the choke valve. Then the vacuum created by the pistons, draws additional fuel, more than normal, into the carb venturi. So more fuel can get into the cylinder, even though much of it is sticking to walls and forming droplets.  We often experience and recognize this as a rough running engine, until it warms up.  This is due to uneven amounts of air/fuel mixture getting into each cylinder.

 

As the engine and all its parts warm up, the nice misty fog does not condense any more. The choke opens up. Some automatically, some manually.  A nice even-flow of air/fuel reaches the cylinders and we experience a nice smooth, even running, idling engine.

 

This image illustrates this phenomena.

 

 

 

Screen Shot 2021-02-25 at 10.34.00 AM.png

Edited by keithb7
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3 hours ago, keithb7 said:

Agreed, fuel evaporates. You might have a little left in the carb bowl. When you floor the accelerator pedal once, if there is enough fuel left, you might get 1 squirt from the accelerator pump into the carb throat. The engine may fire a couple of times then die. You could also not get any fuel into the cylinders. Depends how much has evaporated from the carb.

 

The mechanical fuel pump has to crank over, pumping fuel from the rear fuel tank, up into the carb bowl again. That can take a while of cranking. This is likely what you are experiencing. Refiling the carb bowl is accomplished by cranking the engine over with the starter. This turns the camshaft, which causes the fuel pump to do the work.  You could install an in-line 6V electric fuel pump. You turn it on for 5-10 seconds, before cranking the engine over. The electric pump will fill the carb bowl quickly. 

 

For further depth if wanted:

The fuel bowl is vented to atmospheric pressure. Fuel can and does, easily evaporate. Especially with all the ethanol in it. When the pistons are cranking, up and down, they are creating vacuum. This vacuum is present and manipulated up in the carb venturi.  A low pressure point, less than atmospheric pressure is present now in the venturi.  This little magical situation draws raw fuel from the carb bowl, via the jets into the venturi.  If the car has not sat for an extended period, there is enough fuel in the bowl to allow this to easily happen.

 

Saying that....You needs lots of extra fuel when the engine is stone cold. The reason is, the raw fuel that enters the venturi is vaporized into a very fine mist. Like a heavy fog hanging over a cool swap at dawn in the fall. When the engine is cold, this misty air/fuel mixture sticks to the intake manifold walls, and intake valve ports.  It condenses and form droplets on the walls. So a lot of the fuel does not make it into the cylinder to combust.  So we choke the air supply off. Closing it with the choke valve. Then the vacuum created by the pistons, draws additional fuel, more than normal, into the carb venturi. So more fuel can get into the cylinder even though much of it is sticking to walls and forming droplets.  We often experience and recognize this as a rough running engine, until it warms up.  This is due to uneven amounts of air/fuel mixture getting into each cylinder.

 

As the engine and all its parts warm up, the nice misty fog does not condense any more. The choke opens up. Some automatically, some manually.  A nice even-flow of air/fuel reaches the cylinders and we experience a nice smooth, even running, idling engine.

 

This image illustrates this phenomena.

 

 

 

Screen Shot 2021-02-25 at 10.34.00 AM.png

Very good explanation Keith. 👍

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I have a syrup bottle with a flip top lid in the garage.  If mine sits for more than two weeks, I don't even try to start it with out a squirt down the carb.  I guess the simple answer is drive it more.

 

The other thing is don't pump the gas pedal.  I believe the owners manual says

Slowly push the gas pedal to the floor  and releas to set the fast idle cam

Slowly open the gas pedal to one quarter or one half open

Then engage the starter.  The electrical connection between the starter and choke will close the choke butterfly when the starter begins turning. If gas in in the carb it should start.

Edited by greg g
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On 2/25/2021 at 3:38 PM, sidevalvepete said:

Very good explanation Keith. 👍


I feel compelled to come back and declare new further research, and depth of understanding.  An old book from 1942 era helped me understand fuel droplets and condensation at cold engine temperatures. 
 

Today I happened upon a used bookstore in a town outside my home region. I enjoy seeking out old automotive technical books.  This book seen below was published in 1972. A lot of further research and development occurred since 1942. The section I just read on intake manifolds,  manifold heat, and fuel delivery was fantastic. 
 

I won’t go on to bore you with too many more details.  However, I learned that the ability for droplets of fuel to stay suspended in the intake air is not only effected by air temperature, but also air velocity. The slow moving intake air /fuel mixture at idle can tend to allow fuel droplets to fall out of the air and collect on intake manifold floors and walls. When cranking over to start an engine, the crankshaft and pistons are turning relatively slow. Air is moving slowly thru the carb and intake manifold. Fuel droplets fall out and drop down. The fuel droplets also condense on cold parts (as mentioned in my earlier post). A double whammy as the engine tries to flash up. Add a poorly maintained 6V system and a cold weak battery, the cards truly are stacked against the poor old engine to start. 
 

Eventually as the engine and the A/F mixture gets heated up by the engine heat, now we get good efficient delivery to the combustion chamber. Air/Fuel that has condensed and may have collected at manifold floors evaporates now too. It takes flight now, and finally arrives at the combustion chamber efficiently. 


My goodness, good stuff! Worth the $5 alone I paid for the book. 

 

If you seek earlier automotive technical learnings, this book delivers. 
 

Sorry if I interrupted this thread. -K


 

 

 

80DA0F45-7D21-4C5A-BB3C-63A60E83D849.jpeg

Edited by keithb7
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45 minutes ago, JohnS48plm said:

Herb Ellinger who wrote the book was one of the teachers for automotive engineering when I went to Western Michigan University.   

Herb really gets into the meat. Pretty deep. I quite like his writing and delivery.  This new found book and knowledge, should really help my trouble shooting skills overall. 

Edited by keithb7
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I have a little flip top bottle that i use to prime engines that sit a long time. I get them with friction modifier in them. And save the bottle. I keep one on the shelf in the shop, other one is in my old dodge i use around the yard. Handy and it doesent leak. Other thing is it doesent hold a lot of gas. 2 oz maybe. Way safer then anything else i used. 

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