I have a 1969 L36 big block.  The car only starts after turning it over for a few seconds and releasing the key (back to on).  It may take two or three tries for it to start.  It very seldom starts with the key in start position while cranking.  It is something I could live with, but would be a problem for someone else driving the car.  Any thoughts or ideas?

Not sure I completely understand the situation. But, if it's electrical, the switch is not making contact. If it's turning over at each attempt, it sounds as if the carburetor is bled down, no pressure, it needs to build. Hench the need to crank more. Are you pumping it or setting the choke at all when you first attempt it? Does it have a electric or mechanical fuel pump? 

Thanks for the reply.  I normally pump it one time before cranking it.  The issue is it will crank, but not start until I release the key.  It has the transistor ignition and the mechanical fuel pump.  It is as if the distributor or coil is not getting the proper voltage while the switch is in "start".  It normally will only start after the key is released from "START".

Ignition switches have a number of contacts -- one for START (power to the starter motor) only, one for RUN (power to the ignition system) only, and another for START and also RUN.

It sounds like while the key is in the start position, it is only supplying the START power to the starter, but not the RUN power for the ignition system.  When you return the key back from the start position, it then powers the ignition system, and since the engine is still turning from the attempted starter cranking, it fires off.

This could be a bad ignition switch (located a ways down the outside of the steering column), or maybe a broken wire.

It sounds like you are not getting 12v from the starter solenoid while cranking, but you are getting voltage from the ignition switch in the "run" position. I would suspect a wiring break between the starter solenoid "R" terminal(pink wire at the dist connector, may change to yellow at the starter...it will be the small terminal to the OUTSIDE of the car on the solenoid) to the connector at the distributor. As a test, you could jumper 12v to the pink wire in the connector and see if it fires up properly that way. If so, look for a problem in that wire from the solenoid, or possibly a bad connection there at the distributor connector.

'69 TI wiring diagram

Another thought...it's possible the starter solenoid is faulty, and not making contact for the "R" terminal while cranking. Never actually ran into that particular issue, but it IS possible.

oh...one last thought...you let other people drive your Corvette?!?!!? 🤣 😁

Joel, Thanks for you detailed reply.  With key in ON position without engine running, I have 7.7 v at both the connector going to distributor and at the R terminal on the solenoid.  When I go to START the voltage jumps to 9.8 v at both the connector and at R terminal.  After it starts it maintains the 9.8 v.  It will vary between 9.8 and 10.2 v depending on engine RPM.  I also checked the voltage at the + terminal of the coil and it reads 2.7v which seems low.  Any other thoughts?  BTW, all three kids learned to drive in the Vette.

Steve, I believe you should have battery voltage at the dist connector while cranking. 9.8-10 v prolly won't do it. After starting, with the key in the "Run" position, the resistor wire drops the voltage back down to around 9v. I think what you are seeing on your voltage tests is the voltage from the resistor wire traveling down to the "R" terminal. My bet is the starter solenoid is not allowing full batt voltage to the dist while cranking. I would, as a test, jumper batt voltage to that dist connector(pink wire) and see if it fires up quickly, as it should. If so, I would have to think the solenoid is the problem. If not, the pulse amplifier may be the culprit.

I have a short article on the TI system I will e-mail you. It basically describes the system, and gives a little diag info...but not much. 

Thanks. I will try the jumper wire.