Curly one - brains trust required please! Can will not keep running when hot - splutters and dies.

[hepkat63]

Hi all,

got a problem I just can't iron out - hoping the brains trust on here can help me!

So, I have a 56 Plymouth with a flathead six motor and when the car warms up to operating temperature, it simply dies - splutters and stops.  Exactly like it has run out of gas.

Car has brand new:

Spark plugs

Spark plug leads

Distributor

Points

Condenser

Fuel Pump (manual)

Fuel filter

Coil

Reconditioned gas tank.

 

What I've tried:

Swapped out the:

Distributor (complete - different points/condenser)

Coil

Fuel filter

Timing is at 2 degrees - check.

Removed and stripped the carburetor - put new gasket kit, needle and seat in it.

Bypassing ignition - just running positive wire from battery to positive on coil.

 

Car has an electric fuel pump as well, but only runs for the first three seconds to prime the line.

Gas lines are not close to motor, the heat shields are all installed and as an added extra, I have convoluted tubing over the gas lines as well.

Fuel tanks was completely washed out and acid etch cleaned before installing - so don't believe it is a blockage (else it would do it all the time?)

Car seems to run fine until it heats up (which doesn't take long).

 

What am I missing?

 

[Kilgore47]

Try leaving the electric pump on.  If it still does it then it probably isn't a fuel issue.

[Los_Control]

The first thing I would do is install a spark tester in line to verify you have spark when the problem occurs.

This one is $4.99 at Amazon.

They come in handy. When the engine is running correctly, you will see a steady pattern ... when the engine starts to sputter, you will know if the spark is also getting weak.

At least you will know if it is a fuel or spark issue.

 

Another quick test is to squirt some starting fluid into the carb when it dies and will not start. .... If it does start or tries to start, you know you have spark.

 

Just need to figure out if it is a spark or fuel issue.

 

One other thing, is this engine converted to 12V negative ground?

6V positive ground, the power wire to coil would go to the - side and + would go to distributor .... unless you converted to negative ground.

Should still run OK, but could cause some strange issues ... something sounds goofy here though. ... need more info on the wiring setup.

[Sniper]

Is the exhaust flapper working properly?

[keithb7]

What transmission does the car have?

[hepkat63]

leaving electric fuel pump on fixed the problem - thank you!    All I assume (given that the manual fuel pump is new) is that the manual fuel pump fails when hot, or can't put out the required PSI when hot - or... cam lobe perhaps worn and not actuating fuel pump piston to the full stroke?   I will (in time) replace the manual fuel pump with a different model, but for now - I'm back on the road!

[keithb7]

Some electric fuel pumps, the mechanical pump cannot suck fuel through it. They seem to possibly have some sort internal check valve that can’t be opened by the mechanical pump sucking on that end.  Sounds like you may have  one of these 

Edited April 12 by keithb7

[greg g]

Try blowing some low pressure compressed air back through the fuel line. There is an oillite or scintered brass filter on the fuel pick up. Remove the suction side at mechanical, remove the gas cap and blow the air back through to the tank.  You should be able to hear a steady stream of bubbles c9ming through the filler tube.  If ypur electric pump has a check valve you may need to by pass it or blow through the tank from that side of the line.  Also most mechanical pumps have an internal filter  between the inlet and outlet chambers you might want to check it out.  Another test to do is fuel pump volume test.  It is outlined in the service manual.  Have you ever removed the top of the carb to check fuel quantity?   Keep in mind the old addage that 99% of fuel related issues are caused by electrical problems and 99% electrical issues are fuel related.  This leaves 2% caused by gremlins and are unsolvable until you sell it and the next owner fixes it in 6.93 seconds after chiseling you down on price cuz its a non runner.

Have you checked your coil temp when it shuts down?  It should be warm not burn your finger hot.

 

Edited April 15 by greg g

[soth122003]

You might also want to check that rubber hose from the steel fuel line to the fuel pump input. It may look good from the outside but crap on the inside, causing it to collapse under suction from the fuel pump at speeds above idle. The electric pump will push fuel thru without collapsing it.

 

Joe Lee