Vented Tank for Mach

We will soon be running our lines and installing engine and trans, plus brake lines for our 4 wheel discs.

We have a good charcoal filter but will be using an aftermarket air filter. So we don't expect we will be able to run the gas vapors into carb.

So that leaves us a choice. Install shorty vent line in the back and just leave it open, install a vented cap or run the line all the way to charcoal filter and let it vent at that point.

What have people tried? drawbacks you've found?

Car comes our of bodyshop in a week, we are picking up our custom trar axle house, axles and 3.89 trac lok pumpkin. We will rebuild front suspension and steering including dropped spindles to mount our discs. We will mount brakes, run lines, then install engine and trans. To roll the body with the new brakes and calipers we need to mount our 17" tires and wheels.

Then we take to engine shop to weld in frame connectors and TCP torque arm.

Finally we then go to paint. We want our frame connectors welded in and weight in car so when they paint side striped they stay lined up. After paint we get to work in earnest. New drive line built and custom exhaust with x pipe will go in then we begin putting, glass interior and everything that finishes out our cars. sorry to ramble. pixs of complete body next week.

I think most would recommend running to the canister and either letting it vent from there or fabricating a connection to the new base of the air filter.

Okay, here is my dirty little secret.

My vent is capped off.

My tank is not vented in any manner, other than the fact that the cap seal is really fairly poor in the first place.

I have never noticed any ill effects of running the system in this manner and when I open the gas cap there is no sign of pressure or vacuum.

I have a canister stashed away in my parts collection, but until I get a good reason to install it on the car, I see no point in carrying around 7-8 extra pounds.

+1, Jeff. I did a nice job of painting the canister and it's been on the shelf ever since. The rebuilt 351C runs great without it.

I think most would recommend running to the canister and either letting it vent from there or fabricating a connection to the new base of the air filter.

Click to expand...

Letting the canister vent is what I am doing for now. I tried capping it and the tank built pressure. I left it open and the garage smells like fuel.

+1

Okay, here is my dirty little secret.

My vent is capped off.

My tank is not vented in any manner, other than the fact that the cap seal is really fairly poor in the first place.

I have never noticed any ill effects of running the system in this manner and when I open the gas cap there is no sign of pressure or vacuum.

I have a canister stashed away in my parts collection, but until I get a good reason to install it on the car, I see no point in carrying around 7-8 extra pounds.

Click to expand...

If you have the vent sealed and notice no pressure build up.

You have a leak somewhere - probably the seal on the tank to filler tube or the gas cap but you have a leak.

Many of the after market air cleaner bases have provisions for installing something like this http://www.summitracing.com/parts/trd-2192/media/images that might work. Chuck

Letting the canister vent is what I am doing for now. I tried capping it and the tank built pressure. I left it open and the garage smells like fuel.

Click to expand...

Check to see that the vacuum hose above the gas tank isn't pinched between the tank and the tank hanger.

-Kurt

If you have the vent sealed and notice no pressure build up.

You have a leak somewhere - probably the seal on the tank to filler tube or the gas cap but you have a leak.

Click to expand...

I agree-the leak is the poorly fitted gas cap. Or some folks might refer to it as vented.

If you have the vent sealed and notice no pressure build up.

You have a leak somewhere - probably the seal on the tank to filler tube or the gas cap but you have a leak.

Click to expand...

I agree-the leak is the poorly fitted gas cap. Or some folks might refer to it as vented.

Click to expand...

Hey you have a 1 of 1 with a vented gas cap

If you have the vent sealed and notice no pressure build up.

You have a leak somewhere - probably the seal on the tank to filler tube or the gas cap but you have a leak.

Click to expand...

I agree-the leak is the poorly fitted gas cap. Or some folks might refer to it as vented.

Click to expand...

Hey you have a 1 of 1 with a vented gas cap

Click to expand...

Mine vents about every 150 miles when I have to fill up:dodgy:

My wife says I vent my gas tank daily.

Wait, what were we talking about?

The 71 mach1 looks like it has a charcoal canister. The origional "pop-open" gas cap

looks like it has a vent also. I heard these pop-open type were unsafe in a rear collision so I got

a Scott Drake reproduction "pop-open" gas cap. The fit and finish is excellent

and installed easily. It has a separate twist on gas cap under the stock looking pop-open

cap. The package says it fits 71-73.

The question is are these Scott Drake caps vented?? or is it vented into the charcoal cannister?

It doesn't say "vented" on the cap or package.

It doesn't hiss when i open the cap and I don't smell gas when the cap is on.

Also there's an open 3/4" nipple hole on top of the cannister. Is that supposed to be hooked upto something?

There seems to be a slight gas smell in that area, but it is also close to the carb so not sure it isn't from that.

That is where the hose goes back to the air cleaner.

All the caps are "vented"...DMV failed me the first time because the cap failed the vac test. I called the main office and they admitted that my car came with a vented system which required the cap to allow air to pass.

None of the caps on our years came vented hence the need for the vent line to charcol canister then to the air cleaner. Usually the vent line will get clogged or pinched and most will start to smell gas in the garage on shut down due to it venting to the atmosphere. Proper venting is also important to get proper fluid flow to the carburator. Plugging the vent line will cause the gas not to flow properly kind of like pinching off a straw while trying to drink.

So if the caps do not allow any air into the tank how do we prevent a vac situation when the pump is suckin fuel and the air cleaner housing/charcoal canister are sucking fumes out of the tank? My caps would not hold vacum at DMV because they allow air to enter the tank when acted upon by a vacuum. I call that a vented system. In our case the vent includes a vapor canister.

You have a bad or incorrect cap

71-3 caps are not vented

The tank can never go into a vacuum or be pressurized. It is open to the atmosphere in the air cleaner thru the charcoal canister.


You have a bad or incorrect cap

71-3 caps are not vented

The tank can never go into a vacuum or be pressurized. It is open to the atmosphere in the air cleaner thru the charcoal canister.

Don