1939 Special Sputters, Stalls When Hot

[JRHaelig]

My '39 was running well for the past year or so until it developed a new habit of stalling when the engine is at operating temperature for 20 minutes or so.

 

It will start fine and run fine until then.  The first symptom is sputtering and hesitation in the upper revs of second gear, which calms down once in third and the revs reduce.  Then  in short time, the problem surfaces at lower revs, followed by stalling.

 

20 minutes on the side of the road and we are ok again, albeit the problem re-surfaces a bit quicker as the engine is already hot.

 

I use a toggle switch as an ignition switch after the column mounted switch gave up.  This could be a significant clue as the car was showing same sputter/stall before I substituted the toggle switch.

This toggle gets noticeably warm to the touch during operation

 

I have a freshly rebuilt carb (done after this problem started)

new coil - installed prior to current problem

new condenser - installed after current symptoms surfaced

electric fuel pump - installed prior to current problem (should rule out vapor lock - no?)

 

It's pretty frustrating to go from a reasonably well-running car to one that can't be driven more than 20 minutes.

 

I certainly think it's something electrical as impacted by heat, though.

 

Is there a resistor that could be failing?  What other thoughts might you guys have?

 

Thank you as always -

 

[Bloo]

1 hour ago, JRHaelig said:

This toggle gets noticeably warm to the touch during operation

 

I would start by fixing that, and continue if you still have trouble.

 

I would also be wondering if the coil is drawing too much current, since there has been trouble with 2 different switches now.

 

AFAIK there is no ballast resistor on a 39 Buick.

 

 

[MCHinson]

I would lean towards a loose or dirty connection somewhere in the electrical system which develops more resistance when it heats up. I would clean all of the connections that I can find, including grounds. I would also probably try another condensor. It seems that poor quality new condensors is a fairly common occurance these days. I would try to find a US made condensor, possibly at a NAPA. After that, I would also try another coil. If the coil was installed prior to the current problem, and the condensor after the problem started, I might even try another coil before trying the condensor. 

Edited August 4, 2019 by MCHinson (see edit history)

[Morgan Wright]

How thick is the gasket between the carb and the intake manifold? It's supposed to be a big thick phenolic gasket maybe 3/4 inch thick, to stop heat from conducting from the manifolds to the carb. I've seen people pile multiple gaskets there, maybe 5 gaskets of 1/8 inch thickness to make a total of 5/8 inch. Overheating of the carb causes vapor lock.

[BuicksBuicks]

The switch shouldn't be getting warm unless its bad; just replace it.

 

As for engine going bad after 20 minutes, have a look at the carburetor heater; its powered by the exhaust. The butterfly valve that operates this system will often seize from rust; make sure you can rotate this valve shaft easily with a screwdriver in the thermal spring center slot; it should move freely. If it's stuck, you will need to get out your copper hammer and tap the valve butterfly hinge front and back until it moves. Once it does get moving, pull the thermal spring off and put it back on backwards. That will kill the heat riser function.

 

The heat riser/carb heater was fine for pre-war cars but doesn't work with modern fuels. Your engine may run a bit rough to start with but will run smoothly after a couple of minutes.