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nmehdikh

Fuel tank vent / Evap tank / EFI question

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So, I'm in the middle of converting my car to EFI/ITBs. I have a thread in the project forum. But I had a specific question about tank venting.

I'm running THIS tanks inc pump, which has it's own vent opening. I'm trying to get rid of whole evap tank system and trying to figure out what to plug, and what to route where.

A post in this thread suggests to only run rear tank pipe to the filler neck, then plug the rest of the tank fittings to get rid of the evap tank.

So what do I do here?
A : plug all the tank fittings, then run the tanks inc vent to the filler neck?
B : plug all the tank fittings except the rear one, run the rear to the filler neck, then vent the tanks inc somewhere else?
C : plug all the tank fittings, plug the filler neck fitting, and run the tanks inc vent somewhere else?
D : something else that I'm missing?

Also, does anyone make a line of fuel safe end caps for the tank openings? or do I have to do a stretch of fuel hose and bolt method?

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What year Z would help.

 

You will need to keep line 8 or line  7 and route it to where line 5 attaches  to the filler neck in the picture below.

 

Look at the picture and you will see why you need to keep the line in addition to venting the tank on hot  days.

fuel_tank_layout.jpg

Edited by Miles

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45 minutes ago, madkaw said:

On my 71 , I ran the vent fitting on my Tank Inc in flex line all the way up front to the original vent valve on the fender . 

797587FB-807A-47F7-9A99-16E3A92B0225.jpeg

I would be worried about the engine vacuum drawing in liquid fuel. I did something similar and wondered why the original vacuum line was rock hard and it was from drawing in liquid fuel. Sucked it up through the PCV valve into the intake manifold.  Originally that line connects high on the vapor tank to draw in just vapors. Vapor tank does a great job keeping liquid fuel out of that line. Personally I wouldn't remove it.

 

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3 hours ago, Miles said:

What year Z would help.

 

You will need to keep line 8 and route it to where line 5 attaches  to the filler neck in the picture below.

 

Look at the picture and you will see why you need to keep the line in addition to venting the tank on hot  days.

 


Car is a 73 240z, sorry forgot to mention it.

I'm having trouble understanding why line 8 specifically gets connected to the filler neck. What's its specific purpose? Is it just so when I fill the tank full, the excess goes to the filler neck instead of the vent line?

My tanksinc pump sits on the flat portion between line 7 and line 8 if that makes any difference here.

 

 

1 hour ago, madkaw said:

On my 71 , I ran the vent fitting on my Tank Inc in flex line all the way up front to the original vent valve on the fender . 

 


My fender vent line is non existent, so I'm trying to figure out another solution. But thanks!

Edited by nmehdikh

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Note that the tank has a bulge on top. When the tank is filled air becomes trapped in that bulge if there is no way for it to escape. If the air can't escape then the gas tank will not be able to be filled all the way.  Think of inverting a glass and submerging it in a sink filled with water.  The air stays trapped in the glass.

 

Also note that gasoline expands when it gets hot in the summer.

 

In the early 70s the US required that automakers had to capture hydrocarbon fumes/vapors  escaping the fuel system. The tank and all of those hoses make up a vapor recovery system.

 

The purpose of the vapor tank and  those hoses was to capture the fumes and pass them through a carbon filter and suck them back into the engine to be burned  (see your FSM).  It also serves as a vapor expansion tank.

 

It is designed as a closed system. The stock gas cap is not vented.

 

The vapor tank collects gas vapor and serves as an expansion tank. As the gas in the tank expands it pushes the fumes/air into the vapor tank.

 

So the reason you connect hose 8 to the filler pipe is so air trapped in the top bulge has somewhere to go as the tank is filled and/or gets pushed out by expanding gas on a hot day. I used fuel injection hose to connect the tank bulge to the filler pipe.

 

So when filling the tank or gas expands on a hot day where will that air go when the vapor tanks is removed?  The air wiil escape through a 1/16in to 3/32in drill hole ("breather hole") you make in the gas cap.

 

Do not top off your tank after removing the hoses and the vapor tank because on a hot day gas will expand and  will be pushed up into the filler pipe and escape around the gas cap and through the small "breather" hole. Just fill until the hose shuts off.

 

Note that the vacuum switch on the inner fender probably is corroded and plugged up.  Every one of those I inspected was completely plugged.

 

If you do remove the hoses, you will have to weld or braze all of the tubes on the gas tank closed.  Do not just plug the tubes. Think collision.

 

Of course if you plan on getting the engine swap certified by the California DMV you can't make any of these changes.

 

Recommend that you search the forums for more information before you do any modifications. There are many many posts on this exact subject.

Edited by Miles

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10 hours ago, BJSZED said:

I would be worried about the engine vacuum drawing in liquid fuel. I did something similar and wondered why the original vacuum line was rock hard and it was from drawing in liquid fuel. Sucked it up through the PCV valve into the intake manifold.  Originally that line connects high on the vapor tank to draw in just vapors. Vapor tank does a great job keeping liquid fuel out of that line. Personally I wouldn't remove it.

 

Actually - the way that valve works there is no direct air route from the PCV to the tank. What opens the vent valve is pressure build up from the tank. You can test the valve by trying to suck air thru it. 

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50 minutes ago, madkaw said:

Actually - the way that valve works there is no direct air route from the PCV to the tank. What opens the vent valve is pressure build up from the tank. You can test the valve by trying to suck air thru it. 

On my 72 it connects to the block breather pipe and vents to the crankcase and then to the pcv valve when there is engine vacuum pulling on it. It will draw fuel in if it's in the line. Witnessed it. 

Vapor tank is a fuel/vapor separator, makes sense why the original line is connected to the highest point on the vapor tank. 

Edited by BJSZED

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Then the valve was defective if I understand the way it works correctly. And I believe the vent line goes to the valve - not the crank breather tube. Valid point about vent line being higher than tank for sure . 

Edited by madkaw

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