Hot coil

[Pascal Zundel]

Hi,
My engine starts well when cold but often refuses to start when hot. Then starts at the first attempt if you let it cool down.
I first thought about vapor lock. Until once when it refused to start even after waiting for more than 1 hour and both fuel pump and carburetors where cold.
I then tried to pull the coil wire from the distributor to boost the spark. It fired at the first sollicitation.
I changed sparking plugs, coil and distributor condensator. It started OK. I took a short drive and tried again. The engine eventually fired but this was very close. The new coil was hot; abnormally so given the short distance covered.
What do you think? Why is the coil getting hot?
Battery's voltage too high (it's a 6-volt Optima - delivering 7 volts+)? Dead voltage regulator?
Suggestions are welcome.

[Mike Wilson]

Could be a bad coil. I'd try swapping it with a known good one insuring it's correctly hooked up.

Mike

[Fred Winterburn]

Also check your points gap. Too much dwell will make the coil hot. A small points gap increases the dwell and it will also lead to a weak spark as more energy is lost through arcing at the points contacts. Also, once the coil gets really hot, the resistance of the windings increases which will also reduce coil output. Fred

Hi,
My engine starts well when cold but often refuses to start when hot. Then starts at the first attempt if you let it cool down.
I first thought about vapor lock. Until once when it refused to start even after waiting for more than 1 hour and both fuel pump and carburetors where cold.
I then tried to pull the coil wire from the distributor to boost the spark. It fired at the first sollicitation.
I changed sparking plugs, coil and distributor condensator. It started OK. I took a short drive and tried again. The engine eventually fired but this was very close. The new coil was hot; abnormally so given the short distance covered.
What do you think? Why is the coil getting hot?
Battery's voltage too high (it's a 6-volt Optima - delivering 7 volts+)? Dead voltage regulator?
Suggestions are welcome.

[Martin Benade]

What makes the resistance increase with temp?

[Mike Wilson]

Good point, Fred. I should have picked up on the hard starting.

Mike

[Fred Winterburn]

Mike, Could just as likely a bad coil as you suggested. Shorted primary turns perhaps if it's getting hot.

Good point, Fred. I should have picked up on the hard starting.

Mike

[Fred Winterburn]

Probably not a big contributing factor as the negative temperature coefficient isn't huge. Here's an explanation from the web. www.cirris.com/learning-center/general- ... -of-copper

What makes the resistance increase with temp?

[Martin Benade]

Sounds like a minuscule effect.