[scottb5y]

Hi,

Thx for everyone's replies. It's been a while, but I'm posting to close this out as the issue was finally resolved and I hope this might help someone out down the road. As it turns out, I think Franken above was closest with his diagnosis / troubleshooting suggestions.

The problem turned out to be a bad ground in the starting circuit. When the engine was installed, they grounded the battery negative to the frame. So my guess is when it was cold and less resistance, it would start. As it heated up, and resistance increased, it would not. At any rate, running the negative of the battery directly to a cylinder head and the frame solved it.

The longer version of this story is step 1 was to replace the ignition switch. I pulled it and it came apart in many pieces with broken metal tabs, etc. It was badly burned from arcing, so while it did not end up being the core problem, it contributed and needed to be replaced.

Since the problem continued, I finally had some focused time and with the help of a wiring diagram and my old "Automotive Electrical Systems" book, I realized it had to be bad ground. The ultimate hint was when trying to start the vehicle by jumping across the starter and solenoid with the key in the off position, a spark would jump across the transmission linkage to the frame.

Hard learned lesson, but I won.

Thx for everyone's help !