Help, the A roadster is misfiring

[russcc]

Went of out for a ride today. Started out fine, once the car warmed up, it started to backfire and buck. As the day wore on, it got worse & worse, and would only go a few hundred feet before it would not go any further. Usually started right up again. Trailered it home, and it fired right up, and ran ok while I put in the barn. What causes that when it's hot, coil, condenser or ? Thank you Fordbarners.

[Brendan]

plugged fuel line?

[Skrain]

Crud in the carb? Choke mis-set? Needle valve glopped up?

[Tom Wesenberg]

As soon as it starts to buck check to see if you still have a good blue spark 1/4" from a head nut.

[H. L. Chauvin]

Hi russcc,

Humble opinion:

1. You report it starts fine when cold.

2. Then, you report it warms up, runs badly, then it is a "no go":

a. Is it possible "no go" because of fuel starvation ???? or,

b. Is it possible "no go" because of "hot" coil or "hot" condenser malfunctioning ????

3. After it kills & "no go", immediately after, you report it starts right up again & runs fine.

4. Please look first at 2a., above fuel starvation ....... Why?

a. With an engine at full operating temperature, if it were a "hot" coil or "hot" condenser malfunctioning, & one re-started it "immediately", then the coil & condenser would not have enough time to cool off.

b. However, with fuel starvation, in just a few seconds the carburetor bowl could refill enough to run a few hundred feet.

5. First investigate the "real" debris blockage source upstream for fuel starvation, i. e., the fuel tank -- on Model A's, like water, gas never gravity flows uphill -- why continue to clean the carburetor incessantly when the debris is coming from the tank?

Just my 2 cents suggestion where to look first.

[Phil]

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My guess would be sediment in the fuel valve. To test drive till it starts acting ugly,pull over shut the gas valve off, drain the sediment bowl, reinstall but leave it loose (so it is not air locked) turn the gas valve on it should take only about 3 or 4 seconds to fill the bowl.

If it takes longer to fill the bowl drain the tank through a paint filter ( may take quite a while in the valve has sediment) remove the valve on the bottom of the tank. Clean the sediment from the valve. Run gas over and over throug the paint filter till it comes back out with no debris. Install one of the "pencil" filter, that the venders sell, in the top of the valve, hook up the lines, fill with gas and have many hours of pleasant driving.

[Purdy Swoft]

It could be any of the above. If you are running the V8 points setup, the problem could be the condenser. The condenser will fail when hot and in a strain but run again for a while when cold, a bad coil would have the same symptoms but the condensedr is more likely the problem.

[colin1928]

1 more thing to check for moisture in the dissy housing this turns to condensation which rises when hot to under dist cap causing missing and back fire
it happened to me after driving in the rain next day big miss fire
colin

[russcc]

This is a late, May '31 deluxe roadster. Not fuel sediment bowl on the carb, and no filter. Tank is very clean in side, have drained and refilled it with fresh gas within the last month when I added an inline fuel shut off valve to stop fuel seepage through the firewall valve. Would fuel starvation cause back fire or would that be an ignition issue ? Thank you Fordbarners.

[Mike V. Florida]

Originally Posted by russcc

This is a late, May '31 deluxe roadster. Not fuel sediment bowl on the carb, and no filter. Tank is very clean in side, have drained and refilled it with fresh gas within the last month when I added an inline fuel shut off valve to stop fuel seepage through the firewall valve. Would fuel starvation cause back fire or would that be an ignition issue ? Thank you Fordbarners.

There is a filter in the carb.

[tbirdtbird]

Condenser gets a lot of heat; always be suspect.
Take it down the road and back to the house and see if you can get it to act up.
If so, this is an old trick:
pull your modern car next to your A and switch your car radio to the AM band. Assuming you do not have radio suppression wires on your A, you will hear the A ignition in your AM radio. If the sound(s) are uniform, then your problem is fuel. If not, it is ignition.

report back and good luck !

[Patrick L.]

It could be any one of the above mentioned things.
When and how does it start to act up ? Does it seem to be speed related ? If you slow down does it run better ? If so, open the gas cap and give it a run.

[insomniacshotrods]

Originally Posted by tbirdtbird

Condenser gets a lot of heat; always be suspect.
Take it down the road and back to the house and see if you can get it to act up.
If so, this is an old trick:
pull your modern car next to your A and switch your car radio to the AM band. Assuming you do not have radio suppression wires on your A, you will hear the A ignition in your AM radio. If the sound(s) are uniform, then your problem is fuel. If not, it is ignition.

report back and good luck !

Thanks for the tip , always nice to learn something.

[Paul in Colorado]

Originally Posted by tbirdtbird

Condenser gets a lot of heat; always be suspect.
Take it down the road and back to the house and see if you can get it to act up.
If so, this is an old trick:
pull your modern car next to your A and switch your car radio to the AM band. Assuming you do not have radio suppression wires on your A, you will hear the A ignition in your AM radio. If the sound(s) are uniform, then your problem is fuel. If not, it is ignition.

report back and good luck !

You can do the same thing with a small transistor AM radio.

Paul