I have a 78 C10 I have inherited from a family member. It has a new battery within the last 4 or so months, 650 CCA. If I charge the battery to 100% the truck will crank and start. If I take a 5 minute drive and shut it off it will start again with no problem. If I let the truck sit for a couple days and try to start it it will turn over strong for 3-4 seconds but not start. After 5 or so seconds the cranking slows down and after roughly 7 seconds it is down to a 'dead battery click' sound. I can charge the battery, spray some liquid fire in the breather, and get the truck started.

I wonder if the battery is undersized? I have taken the battery out and had it checked at Autozone, they say it is at approximately 80% when the truck won't start but shows as a "good battery." Once the truck is started it runs just fine.

Any suggestions? I have read about possible fuel pump leak that is allowing the carb to drain, but is sure seems the truck should not go from strong crank to clicking in 7ish seconds.

 

check the voltage before you start it and while its cranking and running. autozone can also check it also with their tester on wheels. make sure its getting a full charge, it is possible theres a small drain on the battery and that can kill it overnight