I am a licensed electrician and if the start wire is bad or has too high of resistance when you removed it form the starter you removed the load from the wire and in theory would have the same voltage as the battery. You need to meter the wire while it is on the starter with a load against it. Since it is an intermitant problem I would look for a bad connection somewhere on your start wire.

 

^^ Agreed. Testing voltage with the wire disconnected at one end does not take in account of the voltage drop caused by the load. If the meter showed 11 volts with no load, then the battery is weak, there should be a minimum of 12 volt in this condition.

 

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I'm thinking the battery may not have enough cranking amps. If the engine happens to stop during a compression cycle the starter has to crank through the compression. The fact that it starts when you hook up your amp/booster seems to confirm that. I assume this mini-starter is a gear reduction unit? Did you properlly set the flywheel to gear clearance? Improper clearance can cause binding issues or damage to the starter.

 

^ He gets the engine to turn over by jumping the hot terminal and start terminal on the starter solenoid together, without a jump or charger. Doing that bypasses the start circuit, which is where he should be looking.

 

I see what your saying "Camaro 69" but the solenoid shouldn't require a lot of voltge/current. Clearance could still be an issue.

 

And I see what you're saying too, but don't you think if it was a binding issue it would happen while turning the key and jumping the terminals?
I wouldn't rule anything out till it's fixed, but to me it sounds like a wiring issue.

 

I had the almost identical thing happen to me friend. It really sounds like a bad starter. I replaced mine and have never had the problem since.

 

I had the same problem years ago with my 68 and more recently with my motorhome (which also has headers). I installed a Ford style solenoid on the fenderwell (away from the heat) and jumped the solenoid connection at the starter with a thick piece of copper. The only connection at the starter will be the thick gauge starting wire in this configuration. I have never had the problem again (except when my battery started to go bad). For piece of mind, I would get the battery load tested to take the battery out of the equation. I had to do that yesterday and sure enough my 2 yr old 96 month battery was bad. Crank the engine over with the coil disconnected and see what your cranking voltage at the battery is. It should be at least 10.2 volts. Then I would do as the others suggested and check your battery voltage at the starter solenoid while cranking the engine. It should be clsoe to what you got at the battery while cranking.