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what do these hoses do?


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"the mud,the blood,and the beer"

Nice Johnny cash referance...:D Ya my 620 has that fitting & hoses too. Been disconnected the entire time ive had the truck. The 620's did come with a fuel recovery tank mounted in the wheel well next to the filler neck..mine is also missing that part :cool:

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Those hoses are Evaporative emission control. Evaporative emissions control reduce the amount of gas that just evaporates from your tank. It does not change the power, or put any extra drag on your engine. It is a good thing, do you want your gas just evaporating away, or not. A correctly operating evaporative emission system will improve your gas mileage.

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I wondered what this was too! Saddly the evap spout thing the hose attached to on the top of my gas tank had rusted away and i had to have my gas tank repair guy solder it shut. So I guess the system in not gonna work again!

 

So are the fumes soppose to travel from the tank to the engine where they get burned off? Or do they somehow travel the other way and return to the tank?

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It is the Flow Guide Valve

 

7799.jpg

 

* It is NOT a fuel return line

* 1 connects to the vapor return line

* 2 connects to the air cleaner

* 3 connects to the crankcase (older Datsuns) or Charcoal cannister (newer Datsuns)

 

You have it capped? Bad idea, these Datsuns have a sealed gas tank, and this Valve is for venting the fumes. I guess if you changed to a vented gas tank cap it would be OK.

 

The Valve also controls gas fumes. If you smell gasoline when stopped or when driving, the valve's probably not working correct.

 

Anyways there is details on it here: wiki - Fume Control

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Ok so this is very timely for me as I am about to put my gas tank back on.

 

As I mentioned before, rust killed the evap spout coming off of the top of my tank. so I had it filled.

 

Now, I still have the hose that goes from the filler neck to the evap tank. Is this enough to get the job done, or will I need a vented gas cap? Is it dangerous as is with a stock gas cap?

 

I will attach a pic of the 1200 fuel control ggzilla posted a link to, which looks similar the my 521 system. If the directional paths are the same on the 1600, isn't the filler neck hose to the evap tank dong the same thing as the one I sealed off from the top of the tank?

 

Evap.jpg

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The line with the X over it is actually for gas to run back into the tank. In the little tank, the vapor condense, and liquid fuel runs back.

 

Somehow the tank system has to be vented. The little tank is not for venting. In this system, the tank vents to the crankcase. Then when the engine is started, the vapors are sucked up into the air cleaner and burned.

 

Older vehicles had a vented gas cap, and the fumes when straight into the air (cough, cough).

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The line with the X over it is actually for gas to run back into the tank. In the little tank, the vapor condense, and liquid fuel runs back.

 

Somehow the tank system has to be vented. .

 

OK, so now that hooking that hose back up is not an option, is my only option to get a vented gas cap? Or pay to have a new spout welded into the old spot?

 

How do rat rod fuel cells work? Do they compesate for this?

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Ok, I did some reading on teh H.A.M.B. forum. Looks like the simplest solution is a vented gas cap. But I still have the hose coming from evaporator that used to go to the top of the gas tank. I guess as long as this hose is unplugged the system is vented. BUT if I am right in my understanding, if liquid gas collected in the evaporator, it would leak out of that open tube, so i need to plug it.

 

The thing I don't understand is why the arrows in the 1200 diagram suggest the flow of old hose moved up toward the collector, not down toward the tank. I guess, naturally, it would go both ways. And they just didn't indicate it on the diagram.

 

 

EDIT, but wait, if I block off the lower tube from evap tank, will gas collect in the bottom of that little tank with no where to go? Almost sounds like I need to switch that that disconnected lower hose the the fillerneck spout, and cap off the hose that currently goes to the filler neck. Then use the vented cap.

 

 

MAn this is a confusing read! Appologies.

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Bad idea, these Datsuns have a sealed gas tank, and this Valve is for venting the fumes. I guess if you changed to a vented gas tank cap it would be OK.

 

i had a system failure(510)...and the tank actually collapsed (like an AL can) from the vacuum :eek: :cursing:

used the bar soap trick, temporarily, to seal the tank untill i got another.

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I wouldn't suggest venting the tank into the engine compartment (leaving the Flow Guide Valve open at the front). Better to seal all the hoses and use a vented cap.

 

Best to fix the system. It keeps everything nice and un-smelly.

 

The factory cap has a vacuum relief valve in it, to prevent the "tank crushing problem". Make sure the cap you have can let air into the tank. But it's not supposed to let air out.

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Even with the hoses dissabled the tank is going to vent. There is a hose that goes from the tank to the filler neck for gas over flow.

 

It is the same size as the line for the gas vapor return system. It will vent out of the filler neck.

 

 

 

 

 

 

dd:fu:

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