Won't start when hot

1912Minerva

1912Minerva

Junior Member
Hello Everyone,

I have has an intermittent problem with my A Model for a few years where it won't start when the motor is hot. It now happens all the time.
The symptoms are that it will start cold no problems at all (first hit of the starter). After running for 20 minutes or so, if you stop it won't restart for around 30 minutes. If you take a lead off a sparkplug, there will be no spark jumping across to the plug. After a while, you will get a weak spark and then after some more time back to a decent spark and away she goes again (until next time!). I have changed out coil, condenser and points on numerous occasions and not solved the problem. Any further suggestions would be much appreciated as it starting to drive me crazy!

Thanks in advance and regards,

Andrew.
 
Have you tried one of the heat-resistant condensers? Do you have a stock ignition system?
 
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Hi Ray,

Thanks for your reply. I have a stock ignition system and wasn't aware of the heat-resistant condensers. They sound like they might be a good idea!

Regards,

Andrew.
 
Your problem caught my attention right away because I have had the identical problem on 2 cars! BOTH were traced to intermittent coils - worked when cold
but quit after 30-45 minutes. Drove me nuts until I narrowed down to the coil.
 
Anteek29 said:
Your problem caught my attention right away because I have had the identical problem on 2 cars! BOTH were traced to intermittent coils - worked when cold
but quit after 30-45 minutes. Drove me nuts until I narrowed down to the coil.
Click to expand...

YUP bad coil!!

There are only a few items in the ignition system, points, coil, condenser. Of these only two are heat sensitive, condenser and coil. I don't believe any vendor sells any other condenser then an A/L condenser. That leaves coil.
 
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Where are you located and what is the air temp? Boiling gas in the carb will cause similar problems, but you did mention no spark, so my first though is to buy a good heat proof condenser. Next I would check the continuity from the coil to the points to be sure the ignition switch i working correctly and the points conduct to a good ground. A good ground also means the distributor needs a good ground.
 
there are junk parts out there. just because you tried new coil and condenser unfortunately doesn't mean what you think, necessarily.

For example we have tried the cutout with the diode from the vendors many times and they NEVER work, they always go back and now we only get rebuilt originals from Steve Becker.

When this happens, swap in a fresh coil on the spot and see what happens. No worky? swap in a fresh burnout-proof condenser (all the vendors have both kinds, the crappy one and the burnout-proof one) on the spot.

For a well-made USA made coil (if you are still 6V), go to FSI ignitions in OK. They are one of the few remaining sources of the last USA made coils in existence (Andover coils)
 
i agree with tom ck the path of the circuit from the coil to the points fior resistance first. its free and easy to do. ck it when the problem is occuring
 
A neighbor friend experienced the same problem while on a tour. One of the mechanically minded participants said no worry. In five minutes he had replaced the coil, had a cold pop and started the car. Everyone thought he was a rocket scientist but he said Henry didn't make rockets, he made simple anyone can fix cars ! Worth a try especially if you carry a coil in your spare parts package. Wayne
 
Thanks for your replies everyone. I will try swapping the coil next time it happens and see if that fixes it. Someone else suggested that the junction box *might* short out to the firewall when it gets hot. Kinda hard to believe but I pulled the junction box off anyway and it is definitely a possibility. The back of one post had some metal exposed and could have arced to the firewall. Not sure if that is the problem but have ordered a new one and will see. Also ordered a new condenser so will try that as well.
I've also read that the coil might work better upright - has anyone got any experience with that?
Anyway, will keep you posted with what I find.

Regards to all,

Andrew.
 
actually the last terminal box i bought from brattons was well made without the possibility of it grounding.. so maybe older stock had that issue
 
I've also read that the coil might work better upright - has anyone got any experience with that?
Anyway, will keep you posted with what I find.
end quote




Good info above.
I'll address the coil question

An oil coil doesn't like to be tipped upside down and will cause problems as you describe. Where as an epoxy coil doesn't care.
If the car is a normal daily driver, the Petronix #40111 [6v] coil is a good replacement.
 
I had a similar issue that was tied to the carburetor. The float was restricting fuel flow, started fine cold because the bowl was full, the longer I ran the car the less fuel was getting through the carb, also cut out at high speeds. After adjusting the float the issue went away as did the engine cutting out. It maxes out at around 60 MPH now, not that I push it that hard very long. I have read the max speed should be around 65 MPH, does anyone know if that is accurate?
 
Hello Model A'ers,

Just an update on my problem. I changed out the terminal box and am pretty sure my problem is fixed. I haven't been able to test on a long journey on a hot day but on short drives and letting it idle in the shed for long periods, it seems to start much better. It always started cold beautifully but would then often be difficult to start with any warmth in the motor at all. It starts easily now.
The original terminal box has the end of terminal posts very close to the fire wall. While the ends were originally covered in bakelite or whatever the terminal box is made from, over the years, part of one terminal post has been exposed. The reproduction one I got has screws as terminal posts with the head of the screw recessed deeply so it is well away from the firewall. Even so I cut some rubber plugs that fitted into the recesses to make sure there is ABSOLUTELY no chance that any arcing can occur between the back of the terminal post and fire wall.
Hope this helps someone.
Thanks for the help I have received on this forum.

Cheers, Andrew.
 
You might check the coil polarity at the distributor center contact. I had the same situation on my 31 town sedan until I checked the polarity with the LED polarity gauge , mine was reversed and the spark was weakened when hot. Just a thought.
 
Anteek29 said:
Your problem caught my attention right away because I have had the identical problem on 2 cars! BOTH were traced to intermittent coils - worked when cold
but quit after 30-45 minutes. Drove me nuts until I narrowed down to the coil.
Click to expand...

I had the same problem with a coil. I was traveling in the desert with temps above 100 degrees. Every time I stopped for gas the car would start, but cough and sputter for a mile down the road until temps under the hood came down. When you stop temps under the go up. It took me a while to zero in on the coil. when hot it expands and probably the high voltage side of the windings shorted across.

Tom Endy
 
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