ah64pilot

Alright fellas, the "first" and "110 octane" posts are cute but let's get down to business...I have been waiting ever since I proposed this idea months ago.

I installed a RobbMC 1/2" pickup and electric pump on my car last week. I took the factory vent tubes off of the corners of the tank and plugged the factory return tube.

Question: Do I need to put the vent tubes back on or can I just cap them? The gas cap is being replaced with a locking type new cap, so I'm not sure the tank will vent that way.

I'm new to this whole electric scene...but I'll tell you, I don't know why I waited so long...the car even sounds different at idle!

Steve

MDchanic

If you pull gas out of the tank, you've got to let air in to replace it.

Up until about '70 or '71, depending on the model and market, most cars did not have evaporative emission controls, but by '72 all or almost all did.
Evaporative-equipped cars have a sealed fuel system, while earlier cars do not.
The sealed gas cap is an essential part of the evaporative emission system, and is an easy way to pick out which cars were so equipped, while the vented cap is used on non-evap. cars.

I'd say that it wouldn't hurt to reinstall the corner tubes, as they may provide balance, and help the fuel in the tank to behave better while sloshing around, reducing chances of uncovering the pickup, and, most importantly, I would make sure that your new gas cap is vented. If it is a sealed cap, you'll have problems.

- Eric

ah64pilot

Ok, I'll put the tubes back in and connect them to the standpipe. Next question, Is it ok to leave the emission vent pipe open at the standpipe? (The far left tube that would've gone back to the charcoal canister)

Also, I would like to use the 5/16 emission vent tubing as a return from the regulator back to the tank...is this tube competent enough to return fuel through or is there an opening in it that I'm not seeing in the Chassis Manual? Thanks Eric!

Steve

MDchanic

I'd plug it and vent it through a vented gas cap.

I have not taken one of these apart, but that tube should be sealed all the way down to the other end (unless it's rusted), and should be fine. If you're not sure, you could always run the pump for a few seconds and then check for leaks.

You're welcome .

- Eric

2blu442

I don't know if I had some other complication going on. But years ago I put a vented locking cap on my 1970 442. When I had a full tank of gas and came off the line hard gas would come spashing out around the license plate I actually had a guy flag me down one day to tell me this! John

ah64pilot

I figured I'd try that but I wanted to know if anyone had experience with it before I sent fuel through it lol! I'm just trying to save money, I don't want to buy 30' of steel or pro lite hose at $8 a foot.

LOL! I went to a car show last Saturday after finishing the pump install and forgot to put caps on the vents (The reason for this post). I topped off the tank and my buddy following me said every time I took off or hit the brakes gas would pour out of the filler or vent tubes at the front...LMAO! I must've looked like such a redneck leaking gas everywhere.

MDchanic

Good call, John!

I always thought that the tank fillers were identical for both types of caps, but they may not be. I'll have to go outside and have a look.

In that case, of course, Steve would want to swap to an earlier tank (ugh.).

- Eric

2blu442

I was under the impression that there was as flapper valve in there somewhere to prevent backflow. But at least on my car there clearly isn't.

The problem with looking like a redneck is the off chance there's a heat source hot enough to ignite it. That would be more excitement than anybody needs in life!!!

MDchanic

Okay, '70 Chevelle SS and '73 Delta fuel fillers LOOK the same, BUT,

The depth of the ridge that the two fingers catch on as you tighten the cap is deeper (taller?) on the '73 than on the '70, meaning that the '73 cap flops around on the '70 tank, and the '70 cap won't even engage the ridge on the '73 tank.

There is probably a way to modify a cap to work, and there may be a vented cap specifically made for the later tanks, but I do not know the answers to those questions.

- Eric

ah64pilot

Well, when I put the RobbMC pickup in I tried pouring out the 4 gallons that were in the tank. I couldn't get a drop out of the filler neck so it must be baffled...I think my problem at the car show was that I topped off the tank completely, so much that at the pump fuel came out of the vents. I think with an appropriate amount of fuel it wouldn't pour out the back with either type of cap.

SBORule

If your tank has a filler tube going down to the tank, it should have a anti-blow-back flapper in there. They put them in there to prevent gas from pouring out the gas tank should your car end up on it's roof.

I would plug those vent tubes you said are leaking and find a locking, vented gas cap. They don't just keep people from stealing gas but also prevent as_ _ _ _ _ _ _ _ _ from putting anything in your gas tank.

ah64pilot

I put a locking cap on it yesterday but I think I'm going to reinstall the vent tubing on it, I just won't connect it to the vapor return line. So weird to put the locking cap on, it fits so well...I'm used to my 40 year old loose and rattling cap lol!

11971four4two

You can always call RobbMc on the phone or email him. Those guys will have answers you can trust.

TripDeuces

On my 66 the filler neck protrudes into the tank about 2 inches. Yours may be the same which would explain why you couldn't get that fuel out.

380 Racer

Steve, I'm not sure on a stock setup (too many years ago) but my cell I have a braided line come up out of the tank with a loop, then goes out of the trunk with a 3/8 fuel filter on the end to keep dirt out. Not sure you have that much room or not?

MDchanic

A shot in the dark, but the newer (emissions) cap fits loosely like that on the older (non-emissions) tank.

Could you have an earlier, non-emissions tank in your car?
If you do, a vented cap will fit right on.

- Eric

ah64pilot

That's almost exactly what mine does. It 90's UP off the RobbMC then loops back around into the 3/8" filter, then comes straight off the filter down to the 90 on the pump slightly below the tank. Then it 90's out of the pump up to the stock 3/8" fuel line...pretty slick. I'll post the pics once I get them downloaded.

No, the tank is stock...I am the 2nd owner of this car and have had it for 23 years. I bought a Stant 10571 locking cap...it doesn't say if it's vented or not but it fits perfectly. No matter, I just got done connecting all of the stock vent pipes back up to the stand pipe. I capped the vapor return pipe coming out of the stand pipe but it should be enough to allow for expansion.

While I had the car up I inspected the bottom side because we're taking it back to the track on Friday. No serious problems, I had a slight exhaust leak at #7 cylinder header gasket that fried the battery cable. I'll get another one tomorrow and route it differently. No worries, just a PITA.

Steve

380 Racer

Sorry Steve, I failed to mention that is how my cell vents. The loop keeps the fuel in and the filter on the end keeps dirt out.

Run to Rund

The stock 1966 setup was a non-vented cap and a vent line that ran up into the trunk and back down underneath. It worked fine but didn't meet later emissions goals. I added a shut off valve to the vent line for when the car is in storage.

11971four4two

The shut off valve in the vent is a good idea! I asked a guy about E85 yesterday and he had an experience with his fuel evaporating away from a vented tank.