Vent issue with 66 bronco

[Rdtrip]

Hi everyone. I have the 66 running and almost done now. I noticed a lot of hissing from the gas cap after running it, and I see the carb is bleeding fuel when it seems the tank has pressure. I only have the rear tank, not dual tanks. 6 cylinder engine and 3 speed manual. I'm thinking the new gas cap is not venting properly, but also noticed the new gas tank from JBG has 2 vent lines that are capped. One may be a return line but I'm using the factory mechanical FP. Should I be running a vent line somewhere up the filler neck from one of those tubes? Leave the other one capped? This does not have any emissions stuff or canister anywhere, and have no idea if it ever did. This is a new body, the 2 other broncos were used for misc parts. Neither donor vehicle had emissions either. Just trying to figure out the venting and gas tank pressurized issues. Thank you!

 

[JB Fab]

I would recommend a vented cap.....

 

[SLOWnEASY]

You definitely need to find a way to relieve the pressure from the tank. I think any off the shelf replacement gas cap you buy is not going to be vented unless it is specifically marketed as a vented cap. Otherwise a standard cap will let air into the tank but not let it back out.

A cheap fix would be to run a line from one of the capped vent lines up near the gas cap and cap it with an inexpensive fuel filter.

 

[bmbm]

Good to hear about your 66 Bronco and these guys solved by recommending a vented gas cap. Just curious if you have an original fuel pump with vacuum for the wipers and where you found it or are you using one you already had? Been looking around for a NOS or old OEM to rebuild. Thanks.

 

[Rdtrip]

You definitely need to find a way to relieve the pressure from the tank. I think any off the shelf replacement gas cap you buy is not going to be vented unless it is specifically marketed as a vented cap. Otherwise a standard cap will let air into the tank but not let it back out.

A cheap fix would be to run a line from one of the capped vent lines up near the gas cap and cap it with an inexpensive fuel filter.

Ok, that's what I was thinking of doing.it will solve that issue. Using actual fuel line and not vacuum line..thank you

 

[Rdtrip]

Good to hear about your 66 Bronco and these guys solved by recommending a vented gas cap. Just curious if you have an original fuel pump with vacuum for the wipers and where you found it or are you using one you already had? Been looking around for a NOS or old OEM to rebuild. Thanks.

I had initially bought a replacement, which turned out to be junk. It wasn't pinned correctly at the cam lever and literally fell apart after cranking it up. I couldn't get fuel any more. So, reluctantly I put the original one back on after I cleaned it up and it works perfectly, vacuum to the wipers do work, albeit very fast. I do NOT have another original, but the owner of this one is coming in tomorrow for a meeting so I will ask if he has any other parts left. I believe the parts bronco he has still has the factory 6 cylinder FP with the vacuum for the wipers. If so, I'll see if he'll sell it. That's the best I can do is ask..lol.

 

[jamesroney]

Good to hear about your 66 Bronco and these guys solved by recommending a vented gas cap. Just curious if you have an original fuel pump with vacuum for the wipers and where you found it or are you using one you already had? Been looking around for a NOS or old OEM to rebuild. Thanks.

Are you looking for a Bronco 6 cyl fuel pump, or a V8?

I have an NOS Carter 289 Fuel / Vacuum pump with the correct 10 screw top if you need it.

 

[DirtDonk]

The 66 would not have come with any of the normal emissions equipment, except for a PCV valve.
Or if a CA model, which might have had an air pump.

But the gas caps would all have been vented, unless the body and filler neck are from a 70 or later Bronco.
Did the body/donor come from a later year? If so, the standard cap for that model will not fit, and would not have two way venting.
But if a 66 cap fit, then you’re in luck because you’re using the Early style. Not sure why it’s not venting, though, unless, as is the case with many modern parts, it’s simply made wrong.

Using one of the supplied vent locations (they are both vents originally) on the new gas tank, will do the job.
Typically have to install it to a charcoal canister, but that’s not 100% required. You can run it up high and loop it, stick a little filter element or one-way valve in it, or do a few things.
But it should vent the pressure.
Could you tell if the hissing you were getting was expelling pressure, or sucking in?

 

[Rdtrip]

The 66 would not have come with any of the normal emissions equipment, except for a PCV valve.
Or if a CA model, which might have had an air pump.

But the gas caps would all have been vented, unless the body and filler neck are from a 70 or later Bronco.
Did the body/donor come from a later year? If so, the standard cap for that model will not fit, and would not have two way venting.
But if a 66 cap fit, then you’re in luck because you’re using the Early style. Not sure why it’s not venting, though, unless, as is the case with many modern parts, it’s simply made wrong.

Using one of the supplied vent locations (they are both vents originally) on the new gas tank, will do the job.
Typically have to install it to a charcoal canister, but that’s not 100% required. You can run it up high and loop it, stick a little filter element or one-way valve in it, or do a few things.
But it should vent the pressure.
Could you tell if the hissing you were getting was expelling pressure, or sucking in?

I see. The other bronco's that were for parts didn't have gas caps on them, the one I bought was a new cheap aftermarket one that doesn't even lock onto the new filler neck, but did long enough for me to realize the air in the tank issue before it vibrated right off the neck. I assume it wasn't manufactured correctly. It sounds like it's sucking air in, rather than the reverse. I did run a 1/4" gas line from the vent tube on the tank up to the top of the filler neck and looped it and installed a small inline gas filter so it can breathe. I'll know later today if it took care of it. Thanks.

 

[B RON CO]

Hi, the metal filler pipe should have a large tube for the fuel to flow, and a smaller tube for breathing. The tank should have nipples to accommodate both. As mentioned, you need a good vented filler cap Good luck

 

[bmbm]

I had initially bought a replacement, which turned out to be junk. It wasn't pinned correctly at the cam lever and literally fell apart after cranking it up. I couldn't get fuel any more. So, reluctantly I put the original one back on after I cleaned it up and it works perfectly, vacuum to the wipers do work, albeit very fast. I do NOT have another original, but the owner of this one is coming in tomorrow for a meeting so I will ask if he has any other parts left. I believe the parts bronco he has still has the factory 6 cylinder FP with the vacuum for the wipers. If so, I'll see if he'll sell it. That's the best I can do is ask..lol.

Thank you that would be great. As far as I know the OE pumps can be rebuilt.

 

[bmbm]

Are you looking for a Bronco 6 cyl fuel pump, or a V8?

I have an NOS Carter 289 Fuel / Vacuum pump with the correct 10 screw top if you need it.

Thank you for that and I should have stated I would need the 6 cyl fuel pump.

 

[toddz69]

Here's a post with a NOS pump for sale:

https://classicbroncos.com/forums/t...yebrow-and-trailer-hitch.329590/#post-3619502

Todd Z.