It wouldn't hurt to try it without the valve. The valve is to keep the fuel evaporation down to a minimum. Your truck may smell of fuel, and you may lose fuel due to evaporation more quickly.

I would try and fix the problem with the vent lines to the canister myself, or a pinhole leak in one of the fuel lines if that is the problem,

Or replace the fuel cap. They do go bad sometimes.

 

The cap is brand new. I only have the problem of sucking air in the front tank. So it must be a leak before the selector valve. I may jsut pull the lines, submerse them in water and blow through the end with the compressor while plugging the other end to find the leak.

 

I don't mean to hijack, but my '81 lacks two lines coming from the canister. One just seems missing. Could this cause an intermittent dying issue?

 

I really don't see how missing connections there could cause your intermittent dying problem.

Of course, my saying this is opening it up for somebody to come contradict that......

 

It depends. If someone plugged or capped the lines going from the tanks to the canister, or from the carb vent to the canister, then it could cause a vapor lock condition.

 

See?
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so I went though everything today. I found my pinhole in the fuel line. But I also found that my vent on the top of the tank only lets air in, not out. Same with my vented gas cap. This doesn't seem right does it? I did put my gas cap back together. I guess I could have been wrong with air rushing in versus out.

 

Why do you say it doesn't let air out the vent line?

 

Because there is a valve preventing it from going out. It has a small plug that is held up to the seat with a spring.

 

Evaporative Emission System introduced in 1970. Was mandatory initially in sold new in CA Passenger Cars, E/F100's and Bronco's.

Since I live (and worked) here in LA LA Land, I'm not aware of other 1970 CA counties, other states emission requirements. But, by the mid 1970's, all sold new in CA light trucks required evap/em...including F350's.

There's a brash young 'un FTE member who was bragging in his sig pic that his (dads) 1976 F350 Stupor Duper C/S (DSO 72) came with no emissions equipment from the factory. Uh huh, yeah right.

I drove out to San Berdoo and looked at it. PCV, EGR disconnected, evap/em charcoal cannister bolted to frame rail, but lines missing. Aftermarket gypo chrome air cleaner replaced original air cleaner.

Smog pump, related brackets, hoses and valves MIA as are the R/L smog pump manifolds that thread into exhaust manifolds. Threaded holes capped off.

CA smog tests all 1976 and newer vehicles, so all this jazz has to be reinstalled and in good working order. If it cannot pass smog, it cannot be registered, and...there is no waiver if the parts are obsolete.

It's either fix it...or park it. This Stupor Duper C/S has been parked...since 2008.

Evap/emission: There is a fuel vapor valve installed at the top of each fuel tank. Lines route from the valves along the right (passenger) side frame rail to a valve on the charcoal cannister.

A corrogated paper hose routes from another valve on the cannister to an elbow that is attached to the side of the air cleaner. The fuel caps are non vented.

 

Remind me never to try and prove you wrong.

 

It will let it out as well, but it has to be at a certain PSI range. Too much or too little pressure will cause it to close. Also if the tank or valve is not in it's proper orientation, IE: turned over or on it's side, it will block everything. This is to keep fuel from spewing out the tank in a roll over into the vent system.