68 300 convertible - Overheating? Gas tank vent lines?
 

New to the forum and glad I found you guys – hope someone can help with this.
We have a 1968 300 convertible. Thirty-six thousand miles, 440 cu. in. (with the Holley) all original survivor car – it was my uncle’s.
Been having a couple problems and I think they’re related.
The car starts and runs fine but once it warms up on a hot to very hot day, the idle picks up a little, it has a slight stumble on initial acceleration (when pulling away from a light) and a slight surge under steady throttle. All of these indicate to me that it’s running hot.
We only have an “idiot” light on the dash and have never gone to the trouble of installing a temporary temp gauge. The hot light does not come on but I don’t have much faith in it.
The other problem is when the car has a full or more than ½ full tank of gas and we start to experience the above, gasoline will piss out of the two vent tubes big time. A little unnerving to say the least. When I’m behind and under the rear of the car checking on the vent tubes, I can hear the gasoline gurgling in the tank. When I release the non-vented gas cap, I get a pretty significant whoosh and the pressure pushes the cap off the filler neck. It’s pressure not suction.
Anybody else ever had this problem with a 440 C body? Any ideas???!!!

vent is blocked

Nope. Both vent tubes are free and clear

cap needs to be vented

Thanks. I tried a vented cap but since the filler neck is almost horizontal, I ended up with another gas leak! Plus the original gas cap (still have it) is not vented.

then there is no way the vents are open

I agree

Guys - I've had both vent tubes off the car. You could drink a glass of chocolate milk through each one.

Plus, gasoline is pissing out of each (on a very hot day and with a full or nearly full tank) so they can't be blocked. Even when the tank is half to 3/4 full, I can still be a "whoosh" when opening the gas cap.

I removed the small canister fuel filter I put on a couple years ago. Just running the small inline porous one that is at the Holley. We'll see if that helps.

If the tank was properly vented it would be neutral, no pressure no vacuum.

First put that stock Holley in the trash... Get a Demond/AVS type carb. Make sure the fan clutch is working....