Ever since I acquired my 1964 356C I was having a problem that had the symptoms of fuel starvation.
With my trusty private mechanic Gordy Smith and counsel from Tom Funk we tried everything.
The issue was that when the engine was just started it would run great but after warming up it just
did not have any power under acceleration. After sitting cooling down for half an hour or so it
started and ran just fine until it warmed up again.
So Tom adjusted the carburetors (when it was cold) and we tore around the neighborhood by his shop and it
ran perfectly. But on the toll road driving home it warmed up and exhibited the same problem.
So over a period of a year we did the following:
- Replaced the spark plugs
- Rebuilt the fuel pump
- Replaced the ignition wiring
- Rebuilt the carbs
- Replaced the gas lines
- Adjusted the valves
- Exchanged the distributor with one that was known to be good
- Asked everyone if they had any idea of what may be the problem
Now I hate to admit that my undergraduate degree is in electrical engineering from one of the big universities.
You will soon see why. Driving home from one of our club events in Wisconsin I was just limping along the toll
road, frustrated with the poor performance of my C coupe. It was running around 3,000 RPM when
it was time to turn on the headlights due to the setting sun. As I pulled out the light switch the engine coughed
and again exhibited the "fuel starvation" symptom. A few more ons and offs with the lights told me that
this was an electrical issue, not fuel starvation.
As we were driving home I pondered my basic transformer theory from my freshman year and thought: Isn't the
ignition coil a transformer and maybe the spark plugs are not getting enough high voltage when the engine heats up?
So the next day I removed the ignition coil (newer looking Bosch Blue coil) and measured the primary and secondary
resistance with my ohmmeter. Everything was within specification. But the physical location of the coil
on the fan housing gets fairly warm after driving a while so I tested the primary while heating up the coil on the
bench--still within spec. Then I let it cool down and repeated the secondary resistance with the heat gun on
the coil. As the coil heated up the secondary resistance eventually dropped in half telling me the secondary
was shorting out when in a hot engine compartment.
Sure enough when I let the coil cool, the secondary resistance went back up to normal.
Obviously the coil was working fine when cold but shorted across the windings when under normal
heat in the engine compartment, lowering the voltage to the spark plugs. A new coil was installed in
five minutes and now it runs like a C engine should both cold and hot. So to all of you taxpayers who
helped me through college under the GI Bill--thank you. I may be a little slow, but I did eventually figure
out this challenging and very basic technical issue.
Pat Yanahan
Midwest 356 Club
May 2009