Engine stumble as warms up

47 COE

47 COE

Junior Member
Hi everyone,
I've been trying to diagnose an issue that seems to be like a rabbit hole.

1947 Flathead 59AB
Stock

The engine will start perfect when cool or first start. But once it starts warming up to about 150 it starts to sputter and stumble. Seems to be miss firing. During this time huge power loss and will not idle off the gas pedal.

I've been searching the forums and have done the following.
Replaced spark plugs and wires
Replaced fuel pump
Replaced coil
Had distributer adjusted and replaced points
Carburetor rebuilt
Replaced vacuum line from distributer
Replaced cap/rotor coil
Verified compression
Changed gas

As I've replaced things little by little the engine seems to last longer until stumbling.

Any suggestions would be appreciated.
 
Sounds like you have checked/replaced most of the likely culprits, but what about the ignition switch and wiring? Does it have a 6 volt coil, and is the wiring still going through the original resistor? Is the generator charging?
 
I do not see where you replaced the condensor. They will cause that problem also.
 
I agree the ignition condenser is one of the likely candidates to cause problems (along with the coil) when it is exposed to heat. Many of the aftermarket suppliers condensers are bad off the shelf. Look to NAPA if you want to replace it
 
fordscript said:
Does it have a 6 volt coil, and is the wiring still going through the original resistor?

If your coil is the modern tube style, I'm sure that is has an internal resistor- if not, it should have an outside mark reading "external resistor required." Recommend double checking your wire to the coil and see if you have it going through the ballast resistor. Ditto on replacing the condensor. The NAPA IH-200 condensor works great. Hope you are able to resolve the issue. Steve
Click to expand...
 
Hi everyone,
I replace condenser a few times during trouble shooting.
The coil is new and internally regulated.

I have just noticed that passenger top side radiator pipe is too hot to touch while the drivers side is just warm and I can hold the pipe and head.

Would you think a failed water pump would cause these symptoms?

Thank you again for feedback.
 
Last edited:
The flathead has been converted to 12v
I have not replaced ignition switch, I'll try this afternoon.

Thank you.
 
If you have thermostats in the radiator hoses, it is likely one of them has flipped over and is blocking the flow. As your problem seems to happen when the engine is at operating temperature, a blocked hose could be the cause. Be sure that a hose isn't collapsing when hot. It is unlikely that a water pump is the culprit unless the pulley or impeller, a rare condition except has come loose on the shaft. We see that in modern cars, but not flatheads.
 
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