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1969 Camaro Mystery - leaks gas at home, but not at the mechanic

We are having a really mysterious issue with our 1969 Camaro. We only drive it occasionally. The last 4 times we started it at home, it leaked a puddle of gas. We have taken it to two mechanics on 3 different occasions to figure this problem out, and while they admit the car wreaks of gas, both mechanics say they can’t get it to leak a single drop of gas at the shop. We just don’t understand, how a car can consistently leak ( a large amount of) gas for us whenever we start it, but it consistently does not leak for the mechanics. Anyone have any ideas? Thank you.

Is it parked inside or outside? If it’s outside, it could be leaking only when the parts are cold, in which case you probably want to leave it overnight at the mechanic’s shop so they can try it first thing in the morning.

Have a Quadrajet carburetor on it? If so, these are prone to internal leaks at the jet well plugs. Most carburetor kits do not come with a seal and epoxy.
This can often be seen by removing the carburetor, filling the float bowl with gasoline, and then waiting it out for a short time. Eventually gas will be seen slow dripping out underneath the throttle bores.

If by external leaks then that could be a sign of vapor locking. Unleaded gas seems to make this problem worse.

Where under the car do you find the puddle?

I have seen mechanical fuel pumps leak intermittently, check for stains on the fuel pump.

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Depending on the carburetor type, it could just be the float bowl gaskets leaking. When it’s stone cold they leak. After some time running, the heat from the manifold/engine expands everything and they stop leaking. BTDT. You should leave it overnight so they can try starting it first thing in the morning when it’s cold…

I use a good low pressure air pressure regulator for that problem. With a rag tightly wrapped around the air pressure hose shove it in the fill pipe and pinch the rubber fuel line closed at the filter then bring up the pressure to about 2psi. I wouldn’t be surprised if every inch of rubber hose on the fuel system needed replacing. I’m sure there have been a few tanks full of ethanol e-15 in the car over the years and old rubber gets flaky with that stuff.

But then there is the problem with old cars tanks that were rusted out above the $2. level!!! Which was nearly half a tank in the ‘good ole days’

Good ideas above, especially about discovering under what part of the car the leak is found (on the ground presumably). I’ve had intermittent fuel leaks over the years on my similar era Ford truck from the fuel pump, the accelerator pump, tank-selection-valve, tank-fuel-level-sender, and where fuel lines connect to fittings. If the location of the leak is just impossible to find, what I’d do in that situation is just replace all the rubber fuel lines and see if that helps. If the fuel pump has never been replaced, now might be a good time for that also.

BTW: I expect OP already knows this, but fuel leaks can be very dangerous. Suggest to carry a big fire extinguisher in the vehicle at all times, and park it outside and away from buildings until the leak is repaired.

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