Fuel tank venting

[Alaw143]

I've seen this here a bit but I'm having trouble with my fuel tanks specifically filling. I can only get 4.7gl in each. I can actually get the fuel to the very top of the fill hose without it going down after waiting. I dropped both tanks, cleaned. I looked at where my 5/8 vent hose attaches from tank to fill hose and realized that there is another port that is capped above where the vent hose comes out, is this the vent hose port that should be used? any suggestions are really appreciated. 70'

 

[bknbronco]

Should only need one vent to let air out when filling. The little one would only be used if you didnt have a vented gas cap. it would let air in to replace the fuel that is going to the motor.

If you get gas up the filler neck id say the tank is full!

Before you put that 4.7 gallons in is it empty? How do you know its empty?

 

[g8rb8t]

not sure, but it could be for the Charcoal filter to connect to the tank?

 

[surfer-b]

Have you checked to make sure nothing has clogged the vent hose, take them off and use air comp to blow them out. I had one that dirt dobbers had gotten into and clogged it.

 

[Alaw143]

Yes, blew the vent hose out, it was clear, no change. Yes the tank was empty. I even waited 5 min to see if level of fuel would drop, nothing...oh and rocked the vehicle, this is on both tanks. There are 2 ports, vent hose on the bottom runs to fill tube, right above that is another port that someone blocked off????

 

[DirtDonk]

What year is your Bronco Andy? Maybe that fitting is something that was added only to the '72/'73 (or whatever year it was) models with the dual tanks and return lines?
If you've got one of those years, perhaps the PO could not find a suitable replacement selector valve with the multiple return ports on it and simply capped everything off?

Long shot, but I don't know any other scenario that would have an additional port on a stock tank.
Perhaps the tanks are not stock? Got any pics for us?

Paul

 

[Alaw143]

Thought they were stock paul,1970, I'll get some pics

 

[turbotim2]

Is the blocked off port a 1/4" nipple? If so, that is a tank vent and should have steel lines that run up to the charcoal canister that is (or should be) on the passengers side firewall. Both tanks vented to the system via a tee just behind the front tank, crossed over to the passenger side and up the frame rail to the engine bay.

 

[Alaw143]

And this line runs to a charcoal canister that allows the tank to fill? Another form of venting? Ok, i am taking a closer look.

 

[turbotim2]

Well the fill vent should take care of allowing the tank to fill... Not sure what is going on there, I was really just responding to your questions about the other vent.

 

[Alaw143]

gotcha, its got me baffled why both tanks fill just above 4 gal.I've required tried every form of filling, but I don't think its that. It fills to the neck and doesn't go down...and yes the tanks are greater than 4 gal

 

[Alaw143]

Ok, just found the exact tank on toms bronco, auxillary tank oe. Its actually, 8 gal capacity. it has the same two smaller ports as mine. Mine is setup as the larger of the 2 holes-(bottom) is the vent tube running to the fill tube. The top one blocked off.