Gas Tank vent

[RG75Bronco]

1. Edelbrock 600 cfm
2.Stumbles on pull off, but after cleaning the carb ran good for about 5 miles then went back to stumbling.
3. Engine performs great except for stumble. It has 8K on a fresh rebuild and runs strong!302, 30 over, RV cam, Gt40p heads, and headers.
4. Added the filter at the tank after locating the black residue. The other filter is located at the carb.
5. New sending unit with sock
6. Carb Choke working as it should.
7. PCV and EVAP/Canister is plugged to factory specs, with the exception a vent does not run from the canister to the carb.
8. Open air filter / Clean
She has been a bear since day one. I swear she has been cursed. A buddy of mine is an old school mechanic and said their is a hand some where in a compartment that is giving us the one finger. LOL

 

[DirtDonk]

I think this deserves it's own thread then. Not sure it has anything to do with venting from the tank.

In the meantime, I should have asked is the black stuff in the intake when you pull the air cleaner off, or is it inside the carburetor's float bowls and such? If it's inside the bowls it's in the fuel. If you have one of the early Edelbrock carbs that included the bowl vent to the charcoal canister, then it's possible your canister is buggered and you're somehow getting it fed up to the carb. Raw gas into the canister maybe, then somehow migrating up to the carb through the bowl vent. Otherwise I don't see that happening.
And besides, I see you said that there is no line directly to the carb. So that pretty much rules it out.

If it's in the venturi and air-horn area of the carb, then it's something else.
If the tank was not properly venting you'd have a negative pressure problem and you'd often be running out of gas. Not just on tip-in, but it would run crappy all the time. You can tell if this is the case by simply removing the gas cap. If the problem goes away, then there is a venting problem. If not, then the survey says, it's something else.

In your first post it sounded like the problem started after adding the new tank. Now it sounds as if it's been an issue since you fired up the engine.
Probably carburetor needs fine-tuning for your setup. Between the bigger cam and headers, it's likely running too lean. If adjusting the accelerator pump to it's max does not fix it, then you need to try playing with metering rod springs, and metering rods.
Maybe even jets, but that's a last resort probably.

In the meantime, hunt for vacuum leaks (even small ones) with some kind of spray testing method. And if the PCV is not the right one for your engine it might be allowing too much air in when you don't want it. Great for high-altitude running, but basically a big vacuum leak at lower elevations.

Good luck.
But I think it deserves it's own thread.
(which will make it extremely funny if it gets narrowed down to a venting issue with the tank!%))

Paul

 

[DirtDonk]

Oh, and the black sooty(?) stuff on the inside of the carb, is probably "overlap feedback" for lack of a better term) from the cam. Since the air filter is clean, it's a good bet that nothing is getting past it in enough quantity to coat the throat.
So it's fuel and oil gasses passing up into the carb from the intake most likely. Could be indicating some kind of an issue, or not. You may need to remove the air filter to watch what happens while the engine is running, then while it's off after a run.

Paul

 

[RG75Bronco]

1. Only in the float bowls of the carb. No other location.
2. The fuel tank was changed out due the original was caked in sludge.
3. No lines connect from the carb to the canister.

I will spray the vacuum lines with some starting fluid and see if I find a small leak. I will follow up with you guys afterwards.

 

[DirtDonk]

Sounds good. Thanks.
With the black stuff in the float bowls only, then the only two ways in are either the vents (which are inside the air filter area and less likely I think), or the fuel line and through all three filters! I've found stuff still gets past regular fuel filters in all of my carbs, so perhaps that's what you're dealing with too.
Maybe your fuel lines still have a buildup of some gunk that needs to be finished out before it disappears finally.

But that would mean a more-often schedule of replacing filters and/or just replacing the fuel lines while you're at it.
With the new tank you're ahead of the game.
If your lines are not that old, maybe a can of gas system cleaner through a few tankfuls would help.

Hmmm, I wonder if you're getting some nasty fuel at the filling station? Do you go to the same one every time, or most of the time? I wonder if they've got something in the fuel that's either passing through the filters (all three of them!) of if one of the additives is reacting with something in the carburetors?
Or maybe some of the old rubber and/or factory plastic fuel line is deteriorating too. Might be worth replacing since it's only a little extra work, and not that expensive depending on what you use.

Anything is possible these days I assume. But it's hard to narrow the sources down sometimes.
Good luck.

Paul

 

[gr8scott]

Regarding the off-idle stumble, I experienced this back when I ran a Edelbrock 1405 600 cfm carb. What fixed it was replacing
the stock accelerator pump (mine was pink) with this blue one. Don't know how or why, but it worked. Can also be found at most auto part stores.

https://www.summitracing.com/parts/edl-1470

 

[RG75Bronco]

1. All of my fuel lines were replaced when the new tank was installed.
2. I have the blue accelerator pump in my carb. Thought it may be bad so I have changed it out with another new one and no change in the stumble. I even adjusted the pump. The carb was cleaned and installed on another engine and ran like a champ.
3. Fuel has come from different locations. I have ran some leaded fuel and it improved

We will figure it out with all of these experienced techs on here.
Thanks

For 9 months I chased a vibration at 55 mph that would throw you out of the seat. Come to find out one of the teeth on the ring gear was pitted causing the problem. Rebuilt the chunk and that took care of the problem. I should name her Christine.

 

[RG75Bronco]

Paul,

You mentioned a possible issue with the PCV system. You may be on to something. When the engine was built I installed GT40p heads. The lower end of the engine is the 1975, 302. So the Gt40p heads were worked at a machine shop. I installed them using the rocker arms and guide plates. However, I used the original 75, 302 push rods and adjusted the lift to 1975, 302 specs. I have researched the push rod length and the 72, 302 is 6.885, and the GT40p is 6.272. What I have not determined is the height of a flat tappet lifter Vs. roller lifter. I believe my best option is to purchase a push rod measurement tool and take a measurement. I have tried my best to search the forum to see what others have had to do in this type of swap with negative results. I am technically challenged! But I believe there is a possibility that the engine valve train system could be the culprit in the mystery of the fine black fine residue in the carb. If anyone has complete a swap please chime in as to hoe did you set up your valve train system.
Thanks in advance

 

[1970 Palmer]

In my Hot Rod I had a similar issue venting my tank. I ended up fabricating a vent line from a 3/8" steel tube. It went from the gas tank vent fitting, straight up inside the trunk to the highest point possible, then I used my tubing bender to put about four 360 degree circles into the tube at the top. The tube was then rerouted back down, through the floor. I used a Ford carb. 1/8" NPT fuel filter tapped into the hollow frame rail. A piece of rubber gas line connected the fuel filter to the vent line. By using readily available automotive steel tubing you can fabricate this in pieces and joint them together with unions.

This system worked well for me for ten years, no dripping gasoline, and stopped the gas fumes inside the garage. I think the key was the LOOPS.

John

 

[RG75Bronco]

Thanks I believe I have valve train issues.

 

[RG75Bronco]

Up Date: Removed the charcoal canister turned it up side down and small particles fell out. Removed gas tanks clean, fuel lines clean and where rubber connected it was replaced. Open the carb up and found a light coat of the black residue. Now this is after the install of the second fuel filter at the tank. Removed the edelbrock filter and found a piece of black substance that was about 2 mm and hard. Not sure if it was charcoal due to it being wet and fragile. I haven't got the carb back on yet as I am performing a pushrod measurement and waiting for the tool to arrive.

 

[Jaybr]

Searching threads trying to figure out how I'm going to vent my M1A1. I found the Vapor Trapper in another thread and ordered one to use as my charcoal canister. Also found these rollover valves that have a float in them to block any fuel from getting in the tube. Once I figure out what size threads are on the vent connector on the M1A1, my plan is to replace the hose barb that came with the tank with one of these valves and run a line up to the Vapor Trapper mounted on the firewall.

What say the experts, will this work?

 

[blubuckaroo]

Has anyone just plugged the extra vent, and only used the vent gas cap?

A vented cap only vents one way. If this is your only vent, the tank can build pressure.

 

[blubuckaroo]

So have a BC broncos gas tank I'm currently using an anti roll over vent valve mounted above the rear tail light. I'm not a fan of it when the tank is full any little angle the gas comes flowing out. Which gets real annoying on a long winding trail ride.

What is everyone doing to vent there tanks?

https://www.summitracing.com/parts/...MIztmkoM6G6gIViZWzCh16TwOvEAQYASABEgLJZvD_BwE

Where is the gas coming from? The gas cap or vent?
https://www.jalopyjournal.com/forum/threads/fuel-tank-issues-falcon-rancheros-wagons.807853/

 

[DirtDonk]

I found the Vapor Trapper in another thread and ordered one to use as my charcoal canister. Also found these rollover valves that have a float in them to block any fuel from getting in the tube. Once I figure out what size threads are on the vent connector on the M1A1, my plan is to replace the hose barb that came with the tank with one of these valves and run a line up to the Vapor Trapper mounted on the firewall.

Don't see why that would not work. As would a standard replacement canister for that matter.
Some nice valves in that link, but is brass still compatible with modern fuels? Or maybe I'm thinking of copper, but it seems to me there have been plenty of horror stories about fuels interacting with certain metals.
Maybe stainless or coated metals are the answer.

Paul

 

[DirtDonk]

Up Date: Removed the charcoal canister turned it up side down and small particles fell out.

Sorry don't remember seeing this back then RG. How are things going so far?
Seems like since it's a charcoal canister, if you turn it upside down then some of the granulated charcoal might fall out? Never tried it myself, but maybe it's normal or maybe it's a sign of failing.
But I still don't see how it can get into the carburetor's float bowls.

Open the carb up and found a light coat of the black residue. Now this is after the install of the second fuel filter at the tank.

Even with two and three filters, I've had buildup of some kind of junk or another inside the carburetor. Almost seems like the fuel itself is letting something come out of suspension (something small enough to pass the filters) then build up inside.
Don't have an answer for it, but it's all too common after some driving time.

Removed the edelbrock filter and found a piece of black substance that was about 2 mm and hard. Not sure if it was charcoal due to it being wet and fragile.

Doubt it. Besides, where would the charcoal have come from? It's pretty nigh on impossible for it to have crawled back up the long vent line back into the tank, only to get sucked past the sock filter and into the secondary filter. Just doesn't seem possible even if the charcoal has degraded and maybe got flushed backwards when some gas made it to the canister and then took some charcoal media back to the tank with it when it backflushed.
But it usually does not back flush like that, even if it does get to the canister up front. Maybe if you were parking it on a big downhill for an extended period, then parked it on an uphill for an extended period?
Unless there is some kind of recurring pressure differential between the tank and atmosphere pushing stuff around, I just don't see it.

Got a pic of this gunk?

Paul

I haven't got the carb back on yet as I am performing a pushrod measurement and waiting for the tool to arrive.

 

[DirtDonk]

Has anyone just plugged the extra vent, and only used the vent gas cap?

Missed this one too apparently. Glad buckaroo brought it back up.
Is this the '68 we're talking about? If so then you already have a "vented" cap because that's what they came with instead of the charcoal canister.
Is that what you meant?

A bit of confusion on the naming of them anyway, as an early cap is vented both ways (in and out) while a later cap is still vented, but only inward to help keep air space filled in the tank, but none of the fumes outside.
I'm assuming that not all such caps are even vented one way, as the canister (EVAPorative emissions system) can also cover that duty. At least to a point.

The kicker is that the two types of caps are not retrofittable without some work.
In your case you'd have to change to a later filler neck and use the later cap, but then as mentioned you'd have a pressure buildup if you capped off the tank vent.
In that case you'd have to drill a hole to make your new cap into a fully vented version. Defeating the whole purpose.

So yeah, in your case you can actually cap the vent and use the system just as you have it now. With your early, fully vented cap.
Fully vented was from '66 to mid-'70 sometime. Once the vapor canister system was installed in '70 the caps were changed too, running to about '76 or so.
The '77 is a different animal as well, but not sure if they all were, or just another running change. Probably as long as it has gas doors, it has the unique-to-'77 cap.

So have you been running yours with the tank vent capped off all this time? Or what?

Paul

 

[Jaybr]

Don't see why that would not work. As would a standard replacement canister for that matter.
Some nice valves in that link, but is brass still compatible with modern fuels? Or maybe I'm thinking of copper, but it seems to me there have been plenty of horror stories about fuels interacting with certain metals.
Maybe stainless or coated metals are the answer.

Paul

I assume since the valves you supplied with the tank are brass, brass will work ;-)
the challenge I may run into is the threads in the tank are 1/4 NPT and the smallest valve they sell is 3/8 NPT. I ordered the valve and a 1/4-3/8 adapter from McMaster, hopefully the valve will fit through the adapter and the whole setup will still be low enough to not extend past the recessed area in the tank. I could always drill a hole in the tank and make it work, but don't really want to do that.

And now you have me curious on the metals: I was planning on using Nicopp for my fuel lines.

 

[jamesroney]

Searching threads trying to figure out how I'm going to vent my M1A1. I found the Vapor Trapper in another thread and ordered one to use as my charcoal canister. Also found these rollover valves that have a float in them to block any fuel from getting in the tube. Once I figure out what size threads are on the vent connector on the M1A1, my plan is to replace the hose barb that came with the tank with one of these valves and run a line up to the Vapor Trapper mounted on the firewall.

What say the experts, will this work?

So now I'm the expert?

The answer is "no" it won't work. The M1A1 stainless tank is a work of art. It is the best made fuel tank for a Bronco that you can buy with money. I have purchased and installed several. The guy that designed the tank vent needs to be taken out behind the shed and beaten with a stick.

As you have no doubt discovered, the vent port in the sender plate sits in a recessed pocket well below the fill line. In fact it sits about 2 inches below the fill line. And about 16 inches below the "real" fill line in the neck. So if you top off your fuel tank, the vent port is underwater. If you leave a little air gap, then when the tank heats, and the gas above the fuel expands...it pushes fuel out the vent, and fills your charcoal can with fuel.

The vent location was engineered for a flat top tank, or fuel cell where the vent port is at the top of the tank. It was never designed to sit in a submerged pocket.

I assume since the valves you supplied with the tank are brass, brass will work ;-)
the challenge I may run into is the threads in the tank are 1/4 NPT and the smallest valve they sell is 3/8 NPT. I ordered the valve and a 1/4-3/8 adapter from McMaster, hopefully the valve will fit through the adapter and the whole setup will still be low enough to not extend past the recessed area in the tank. I could always drill a hole in the tank and make it work, but don't really want to do that.

And now you have me curious on the metals: I was planning on using Nicopp for my fuel lines.

it won’t work.
I don’t have time to reply right now, but will later. Take a look at where the vent port is on that tank, and you will see that it is submerged when the tank is full.

It’s a bad design, and you have to change it. 50% of the people run vented caps. 25% run a different vent, and the other 25% full their charcoal cans with gasoline. Or complain about fuel odor. Or never run more than 3/4 full. Or spend all their time at swap meets looking for “the other cap”

I would type more, but I have to go modify the vent on my brand new 23 gallon fuel tank…

 

[DirtDonk]

I’ve heard plenty of good stuff about that NICOP stuff, so you’re probably OK and it probably means that copper is OK. If only when there’s nickel added.