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Well I guess I’m back.


fredges

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Your gas tank is a sealed tank.   There is a small tank under the cover on the bed, that separates fuel vapor and liquid.  The liquid goes back down into the gas tank, and vapors are either drawn into the engine, and burnt, or stored in the engine crankcase when the engine is not running.  It works with the valve in the engine compartment that had a yellow Zip tie on it.

 

Evaporative emission controls do not decrease the power of the engine.  It has the possibility of increasing your gas mileage.

I say keep it.

Edited by DanielC
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Here is a page from the 1970-1971 Nissan service manual for the emission control system.  It should give you some info on what you need to get the fuel tank usable on your truck.

Note that the fuel tank vents through the air cleaner, the flow guide valve (yellow zip tie on your truck) and the vapor separator tank that should be under the cover in the bed.

The vapor separator tank has three hose connections.  Two are in the middle of the tank, one is on the bottom.  The bottom connection drains back into the gas tank, one of the middle connections goes to the top of the fuel filler neck, the third connection goes to the flow guide valve, middle connection on that valve.

The gas cap is not vented.  

If the gas tank is completely full, and you can do this on a 521 because the large diameter of the hose from the filler neck into the gas tank, there is no room for liquid gasoline to go except in to the vapor separator tank.   If your vapor separator tank is missing, you could have a completely full gas tank force liquid gasoline out somewhere on a warm or hot day.

 

Do not top off the gas tank on a 521 truck.

 

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If you have not yet pulled the gas tank, put penetrating oil on the bolts holding the tank in the truck.  Wait a day to so, to let the penetrating oil penetrate.

 

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14 hours ago, fredges said:

There’s nothing under it but a couple grommeted holes. Maybe I can do something cool with that space... hmmm

 fredges:  i deleted mine on my 521

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My winter project this year (since I accomplished some big ones last winter) is to pull the tank out of my truck and restore it. I crawled under there recently and it’s going to be one hell of a time.

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Before pulling the gas tank, clean the exposed thread on the bolts as best you can, and then put penetrating oil on them.

I have found used AFT and acetone in a  50/50 mix makes a really good penetrating oil.

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1 hour ago, DanielC said:

Before pulling the gas tank, clean the exposed thread on the bolts as best you can, and then put penetrating oil on them.

I have found used AFT and acetone in a  50/50 mix makes a really good penetrating oil.

I've got some Kroil... 

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  • 3 weeks later...
On 8/4/2020 at 2:28 AM, hobospyder said:

I'll see about getting them dug out

Thanks Hobo! Hope to see you sometime soon. 

Say, I saw a link on here for a cheap carb rebuilt kit... now I can't find it for the life of me... help? Anyone got a link to a cheap carb kit? I need to give mine an enema. It'll be the first time I've really gone deep in a carb, too, so here we go (que the circus music). 

 

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17 minutes ago, hobospyder said:

Dug out and thrown into the back of the longbed for now. I work 3rd shift now so it'll have to be a Friday or saturday. Direct message to schedule

 

You rock, thanks

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