Gas tank hook up 71demon

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roadripper

roadripper

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Son's demon has a gas tank that has a vent atthe top of the tank and the sender has 3/8"inlet , there is a second line there i beleive 5/16 "dia. Where do we hook the 5/16 line to ?or do i block it off?

We are having fuel delivery issues with this car , starts and runs then stalls and then no fuel in carb , changed filter , checked pump it seems ok , when you take the fuel line off at the pump should the fuel just pour out of the line ? This doesn't any help would be great thanks

20200616_001701.jpg
 
Fuel line should be full of fuel when removed. Have you pulled the old sender out yet? It will have a filter "sock" on it which may be plugged. If it is , I would be concerned about dirt in the tank. If your fuel system doesn't use the extra fitting, cap it off.
 
Murray said:
Fuel line should be full of fuel when removed. Have you pulled the old sender out yet? It will have a filter "sock" on it which may be plugged. If it is , I would be concerned about dirt in the tank. If your fuel system doesn't use the extra fitting, cap it off.
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Car was built 2 yrs ago was a new tank and sender at that time , problably gonna pull sender and see if any issues
 
I dont know. I may be outside the box here, but Does the vented gas cap help the gas flow better than non-vented?
Not sure what set up you have.
 
Is unlikely that yours uses a vented cap, but a good point- you should check whatever vent system you have. Actually this could be be your whole problem- if your tank is not venting.
 
A fellow Fabo member went through the trouble and posted this pic of original gas cap applications. So looks like 68-70 were originally Unvented, 71 and up had vented variations. I forgot who posted this, but thank you and heres a copy of it...
20200616_114412.jpg
 
Look this up in the service manual. There were changes almost every year from 70 and later for the evap emission controls. Only CA cars in 70 had it and possibly 71. First year or two had vapor separator in trunk, then tank was changed and separator was eliminated

NO A BODY uses a vented cap. The evap control cars use "pressure vacuum" relief caps which are NOT the same as vented. The car MUST have a vent. On the emission / evap it is provided by the line going "up front" to the carbon can stuff. You can NOT eliminate that without replacing it. You can NOT eliminate the vapor separator without causing siphon/ leakng problems.

I've said this before. If you are modding a vapor / tank controlled car, best idea in my mind is to mod the filler neck to mimick the 69/ earlier vent.

The filler caps pictured above are telling....about the changes

Best thing I did for fuel boil/ vaper lock was 1...rear mount electric pump, 2....carb isolator spacer........3....fuel / vapor return. Use a Wix filter with the orifice. 33041? 33042?
Go to mymopar and download the 69--73 shop manuals and read them.
 
roadripper said:
Son's demon has a gas tank that has a vent atthe top of the tank and the sender has 3/8"inlet , there is a second line there i beleive 5/16 "dia. Where do we hook the 5/16 line to ?or do i block it off?

We are having fuel delivery issues with this car , starts and runs then stalls and then no fuel in carb , changed filter , checked pump it seems ok , when you take the fuel line off at the pump should the fuel just pour out of the line ? This doesn't any help would be great thanks

View attachment 1715546712
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So does it starve for fuel after driving awhile?
Or does it starve out after initial start up?
What are the conditions when it starves, Hot? Under a load? Idling?
 
71 had two different emission/venting setups for the tank. It depends on the build date on what system your car came with. So if you look up a fuel tank for a 71 you will see an option for "with EEC" and without. I dont recall if it has an additional fitting on the sending unit but it does have many additional fittings on the tank. I also know the cap is different. It sounds like you might be pulling a vacuum on the tank. I agree with leaving the cap loose and give it another run to see if the problem clears up.
As far as hose routing, the FSM should lay all that out.
1971 DODGE DART 5.6L 340cid V8 Fuel Tank | RockAuto
 
Vehicle shuts off during initial warm up , cant even get it out of driveway, we changed sender last night , we have the later tank with the eec emissions that port at the top of the tank is that a vent or is that for charcoal canister ?
 
It is BOTH. As I poorly tried to explain earlier, the evap control system, "the tube" that comes up front IS THE vent.
 
Turns out its a pump issue, were gonna install an electric pump some where lol . Anyone have install pics of where they intalled their pumps? The vent at the top of the tank we are gonna runn a hose to the top of filler neck and tie into that hopefully cures a few things
 
roadripper said:
The vent at the top of the tank we are gonna runn a hose to the top of filler neck and tie into that hopefully cures a few things
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You are going to do...............WHAT!!!!????..............

If you are going to do what it sounds like, then you have just created a NO vent
 
The way it is now , i have a small pc of hose with a air line vent on it. When we fill the tank gas pours out of this vent , without putting a charcol canister up front and running a other line to front ,run it to the filler neck, car has a vented cap should work ? Not sure lol,any thoughts
 
Well if you hook the tank line INTO the filler neck there is no vent. NONE. Maybe I misunderstand.........is the filler neck vented as per the 69/ earlier cars? If so, just plug the tank vapor line and done.

It's as I tried to explain earlier. You need to read the shop manuals through those years and compare them to the tank, and be CERTAIN which tank setup you have. Some of them have an internal vapor separator inside the tank, and some (earlier) require the long vapor separator that sits up inside the trunk. The earlier cars withOUT vapor controls have no such anything, originally, and they have the vent line welded into the top of the filler neck.

1..If you have the pre--vapor control tank (and I guess you don't) the only real practical option is the traditional vent out of the top of the filler neck, look up a 69 Dart/ Valiant shop manual

2...The start of vapor controls used the vapor separator, which connected several lines from the tank to the separator, and the line "up front" which IS the vent. There is no practical way that I'm aware of to get this vent to work "at the rear" because it must end "high" (like top of the engine bay) and it will siphon sometimes

3....The later versions had the vapor separator in the tank and this is even worse. Again you must get the vent line HIGH or it will spill and siphon. Again I know of no practical way to deal with this "at the rear" Where are you going to end it? I "guess" you could run it up high and out the upper corner of the car, but "if" it ever pukes, it will ruin paint. If you run it back down low, it will siphon.

THIS IS WAY ladies and gents, I recommend duplicating the 69/ earlier vent. It's simple. It has no bad tricks. And it works
 
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