Replacing the gas tank on the 77 F100 and see what looks like a vapor recovery set up on the top of the tank. The new tank doesn't have a hole to receive the recovery device. I don't have to go through inspection at this age, but wondered whether I should hook it up or not. Thoughts?

Where does the vapor recovery line lead at the engine compartment?

 

At the engine compartment end, it would go to a charcoal canister, which would capture the vapors so that they could later be drawn into the engine and burned. If you're going to delete that evaporative emissions system, you'll also need to change your gas cap to a vented-style, or else the tank won't be able to breathe air as fuel is drawn out of it, and you'll get fuel starvation as the pump draws a vacuum on the tank.

Downsides of deleting the evaporative emissions system are:

1. Increased hydrocarbon emissions contributing to smog, etc.
2. Gassy smell on hot days
3. You're literally letting some of the fuel you bought evaporate away and not get used

Upside is being able to use the tank you bought that doesn't include a provision for the vent line.

 

If you do delete agree add the vented cap. Also, current vented caps seem to have a pretty high relief valve setting. Of greatest concern, they can let a pretty good vacuum develop in the tank before venting which may contribute to vapor lock. A strategically placed very small hole (eg 1/16") in the cap fixes this problem.

 

Thanks guys.

The vented tank wasn't an option when we bought it. I'm going to cut a hole to make the old connection valid. Seems like the best thing to do. The tank has never had fuel in it so there is no concern for safety during cutting. I will need to fully recover metal bits left over from the cutting though. I'm wondering if I should temporarily install a filter at the tank. I'd hate to damage the fuel pump valves if metal got sucked in. I'm thinking on that one.

Is the charcoal canister the black plastic ball located on the left front inner fender?

 

I'm not sure what the plastic ball is on the driver fender in mine. The charcoal canister looks like a coffee can that's painted black by the battery on my 78 f150.

 

Oh I always run a filter by the tank too as extra insurance. I get the metal ones so it's less likely road debris will split it as easily as plastic or glass filters.

 

Please see comments below in red.

 

Plastic ball is likely a vacuum reservoir.

Charcoal canister can look like a coffee can on the passenger side frame rail, or a rectangular plastic canister:

 

I may remember wrong, but I thought the top vent hole was only one of differenc s in the tank. Check your filler neck vent love ne to make sure it is not on wrong side

 

I think the filler neck vent location was one that varied with model year (round cap vs fuel door)? Still worth checking.

 

There are two differences between the tanks. Tanks with EEC have a hole in the top center of the tank. A rubber grommet and check valve are pressed into the hole. A line goes from the check valve along the inside of the passenger side frame rail to the engine compartment where it hooks up to a charcoal canister. Non-EEC tanks don't have this hole. The other difference is the nipple for the breather line that is located right next to the nipple for the filler hose is located 180 degrees opposite. If you are going from an EEC tank to a non-EEC tank you must also change the fuel cap to a vented style. The EEC tanks are vented through the EEC system and use a sealed fuel cap. Non-EEC tanks vent through the fuel filler cap. If you run a non-EEC tank and a sealed cap the minimum is you'll have fuel starvation problems, at worst a collapsed fuel tank.

 

It seams a good time to ask an old unanswered question..
How does one verify their cap is vented?

 

I drilled the hole, deburred it and reset the check valve. A second filter at the tank will be installed this weekend.

Thanks for the help guys.