My 86 Z-28 has a problem sometimes starting after sitting for a little bit. It doesn't always happen. When it does the car turns over slow like the battery is low or the timing is advanced too far. I have the timing set at 12 degress before TDC. I don't have any spark knock and the car runs really good. I took the battery and starter to AutoZone and they tested them and said they were OK. The alternator is charging too. I've cleaned all the wiring connections I can think of. I'm wondering if the starter is picking up heat from the shorty headers and that's my problem.
Any ideas? I'm about ready to go out and buy the biggest battery that will fit in my car and maybe a mini high torque starter.

 

Reset the timing to the correct base settting then try it.

 

Timing reset and still have a problem when hot. I'm still wondering if the solenoid is bad.