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Car is running fine but curious about the way it's starting.
Turn key on hear pump; crank engine takes a good 6 seconds of cranking before it gets combustion.
If I only crank for a couple of seconds and let off the key it develops combustion and starts. Used to hearing combustion before letting off cranking, you know.
 

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Turn key on hear pump; crank engine takes a good 6 seconds of cranking before it gets combustion.
Something isn't right. The pumps (there are two) should only run for a moment when the ignition is first switched 'on'. Then they should go silent until the key is turned to 'start' and remain powered on when the engine is running. The drive relay control power to the pumps.

If I only crank for a couple of seconds and let off the key it develops combustion and starts.
I would wonder what is system voltage during cranking? If it drops below ~ 10.5V the computers (there are two) will not power up and send the make spark/squirt fuel signals. Connect a voltmeter to the battery (do not trust a dash gauge). See what it reads with everything off (should be about 12.6V) and then see what it reads during cranking. (Our '84 Spider reads > 11V during cranking.) Perhaps your system voltage is marginal.

See the link in my signature to a page of info about the Spider's L-jetronic system and a number of DIY checks you can use.
 

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I had that issue with my 86 when a relatively new battery developed issues. The car would start upon releasing the key from the start position.

Apparently the cranking voltage was just below the threshold for the ignition ECU to turn on and without the cranking load the voltage would spring back fast enough to turn everything on while the engine still had a little momentum. Got the battery replaced, proration fee cost me $0.74, all was well after that.
 
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