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Last year I had an MSD Atomic EFI and a new gas tank (internal fuel pump) installed on my 1966 Impala Convertible. I’m running a stroked 496 BBC. There were some pains to get through, but by the end of the summer it was starting, idling, and running like a champ.

Earlier this week I was out for a cruise with my wife and son when I smelled gas. I pulled over and discovered a puddle of gas under the tank’s vent line. I’m scratching my head trying to figure out how and why that would happen. I removed the gas cap to see if there was pressure built up in the tank, but it was normal...no “whoosh” of air pressure or suction. What could cause what I assume must be a build up of pressure, resulting in a vent puke? The vent is mounted above the tank as it should be. My best theory is that since the shop decided to use my existing 3/8” Steel fuel line as the EFI return line, the engine bay heat might be heating up the return line to the point of boiling the gas, causing pressure to build up in the tank. Does this make sense? I should also point out that I filled the tank the day before this happened.

I’m hoping you all might have some insight on what else might cause this issue and how can I prevent it from happening?

Thanks!

Jeff
 

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I think the problem was due to the difference in ambient temperature from yesterday when you filled the tank to today's over flow.

Big Dave
 

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I would keep it in the back of my mind during fill up. If it never happens again I would say that was the problem. You don't want to waste gas pouring it on the road but you really don't want to have a garage full of gas fumes. Remember gas won't burn, but gas fumes explode.

Big Dave
 
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