my car is a 1970 nova with a 327 with a 750 holley. when you drive it when its hot and stop for a little bit the carb loads up. I noticed over the weekend when i got gas and took the cap off it purged air out and the tant sounded like it was expanded. any help would be appreciated.

is the tank vent open ???

i don't know if your tank or cap is vented, but there should be one or the other...

I'm having the same kind of problem, pressure building up in the tank, when it's closing to empty. The gas cap isn't vented. How do i check the ventilation of the tank?

/M

on a first/second genner there's a vent hose located off the tank filler... maybe it's clogged...

on a third genner i believe there's a vapor return line that loops in the system to a vapor canister... maybe the canister is clogged. possible debris in the hose has clogged it also...

remove the line from the tank and up front in the engine bay and maybe try using compressed air to clear (or check for clogs)

maybe ???

my car does not have a canister or a return line. The smaller hose at the tank is plugged off. any suggestions to make it vent with out smeeling fuel.

connect a hose to it and run it towards the back, along the frame...

a couple/few bucks for fuel line would be worth the test i'd think. hope it solves your issue ;)

I'll give that a try thanks

Buy a vented cap off of an earlier year car if your car is not equipped with a charcoal filtered tank vent. The charcoal filters were installed to keep the California Air Board happy and filter out of the air the fumes from the gas tank. The activated charcoal filter has long since been deactivated by the amount of fumes it has filtered by now (never intended to last 35 years) but it still vents the tank to allow air in so you can get the gas out.

If you are running the required return line without the vent then yes it will pressurize your system and increase the fuel line pressure to the point were it will unseat the needle valve that keeps excess gas out of the fuel bowl. The float has a set pressure it applies to the needle valve to keep it on the seat, as the fuel line pressure builds it pushes against the valve trying to force it open and then floods the carb with gas. Excess gas coming out of the fuel bowl vent then runs into the throttle bores and will flood the engine.

People used to remove the EPA mandated emmisions equipment without knowing what each part does in the hopes of regaining lost power from the muscle car days. Truth of the matter is with the exception of the lowered compression and the EGR valve everything done to prevent emissions has actually improved performance; or has no real ill effects. The charcoal filter added expense to the car but doesn't in any way hurt the horsepower. Same for the air pump, it adds cost but doesn't remove any noticeable amount of power (maybe a third of a horse to drive it). Cats if large enough to allow exhaust gasses to flow have no more effect on the car than mufflers or tail pipes. The PCV valve has an ill effect in the sense that oil in the combustion chamber reduces the octane rating of the fuel charge (promotes detonation), but it doesn't effect overall horsepower either.

Only the lowered compression (done to reduce oxides of nitrogen gas) and the EGR valve have an adverse effect upon the cars actual performance. The EGR valve only works during high vacuum (closed throttle) and can be defeated with a ball bearing in the vacuum line (though all of the exhaust gas plumbing brings in excess heat, and that also effects air flow through out the manifold by being in the way of a straight shot at the ports). The EGR valve feeds the motor the ashes of combustion. We all know that ashes will not burn so it dilutes the tail pipe emissions by lowering the heat of combustion in the chamber robbing power.

The EGR valve is a cheat to get mid seventies cars to pass the sniffer test which was performed at idle. It was a cheap way to allow people who wanted a V-8 to get to the required level of emissions without having to go to EFI. So you can think of the EGR valve as the price of retaining the carburetor that was invented nearly 150 years ago by the guy that founded the Mercedes-Benz company in Germany. Old and crusty, but it still works (just like some of the Mods around here).

Big Dave