EVAP to intake manifold?

[rollinsrods]

Looked around and found a ton of EVAP discussions about removing and such.  Don't want to remove it-it's fuel that has been paid for, so I'm using it.  That said-can I route my EVAP fuel line to my intake or should I drill a hole in the base plate of my Weber and vent it there? I'd rather put it to the intake so it's cleaner looking and easier to work around, but I read somewhere that the vacuum would be bad on a Datsun.

[datzenmike]

Not sure what you mean by EVAP. There is nothing on Datsuns called EVAP. I assume this means evaporation? Maybe explain what you mean.

 

Also is this for the 510 or the 620 in your signature? Weber 32/36?

[rollinsrods]

Evaporation fuel line on the driver's fender of my 620.  Sorry for not being completely clear, Mike.  I've worked pretty hard at making sure all my stock fuel lines and hoses that are connected to the truck stay operational even though I swapped to a non emission intake and exhaust manifold.  It's the last hose left to connect.  I kept all fuel lines and tank set up stock.  And yes, it's a 32/36.  Thanks for any help!

[ggzilla]

Are you talking about the fuel tank vent line? Or the fuel return line?

 

EVAP is Datsun's term for the evaporative emissions system. It is not a specific part.

[DanielC]

On a 521, the evaporative emissions is controlled by a valve that allows fresh air into the gas tank, but any positive pressure in the tank goes into the engine crankcase.  The PCV system draws fumes out of the crankcase. 

If you connect the fuel tank directly to the PCV valve, you could put a high vacuum in the fuel tank.  This could cause the fuel tank to collapse.

[ggzilla]

Same for early 620 - using Flow Guide Valve.

Later 620s use a charcoal canister.

 

None of the EVAP hoses connect directly to the manifold or carburetor.

[datzenmike]

and they shouldn't. Has to use the suction from the PCV valve. 

 

Connecting to the intake could implode your fuel tank.

[bananahamuck]

I drilled a hole on the bottom of my air cleaner housing put in little brass nipple from hardware store and ran a vacuum hose into it... Doesn't suck very hard, but took away most of fumes,, without sucking so hard raw gas is pulled out of tank either.

[rollinsrods]

So I should T into my breather tube hose in order to feed the fumes from the evaporation line to the intake manifold?  I'm taking from the comments that I need to make sure my vacuum vent is going into my PCV valve via the breather hose from my crankcase directly since there is no flow guide valve.  Pics tomorrow...sorry for being lame that way guys!

[ggzilla]

No.no.no.

 

First, we don't know which hose u r referring to ...

 

There are different EVAP parts:

* fuel tank vent

* fuel return line

 

Then CRANK

* PCV hose

 

Which year 620 are u asking about? Is it CAL or FED per the underhood sticker?

[rollinsrods]

FED. Has PCV valve mounted on the intake with crankcase ventilation hose running to that.  Fuel tank evaporation line is what needs hooked up. Fuel return is routed like stock.  I  hooked up the hard line around valve cover back like stock was to the hard line on the passenger side.  I routed the pressure side of the fuel system through a regulator to the carb, which has a guage mounted on it.  Basically the passenger side didn't get changed, but the driver's side was gutted.

[rollinsrods]

1976 is the year.  I know people swap intakes all the time, what do they do with the evaporation line (other than eliminate it)?

[ggzilla]

You keep saying evaporation line, but neither Datsun nor anyone here calls it that. There are two main lines in the EVAP system.

 

The fuel tank vent line? If you eliminate it the fuel tank can be damaged or leak. It needs a vent. Some guys just leave it disconnected and though fumes do come out I have never heard of a fire from it.

 

Maybe someone here will know if the 1976 620 used a Flow Guide Valve or a charcoal canister. Both utilize a valve to route the fumes two different places, and a check valve to prevent backfires.

[datzenmike]

'75 and up 620 used a charcoal canister for fume storage. Earlier L16/18s stored the fumes in the crankcase when engine was shut off. When started the PCV would draw them out.

 

The canister has three hoses.  One to the gas tank vent. Two to the intake although it has a small restriction so it is not seen as a vacuum leak. Three to the vacuum advance on the distributor.

 

 

Fumes from the gas tank are stored in the charcoal during idle or over night. When engine is running but above idle, vacuum pulls open a one way valve on the canister so that the fumes can be drawn into the intake. Simple, foolproof and totally benign in operation. Some later California systems have a hose from the float chamber to collect these fume also.

[Charlie69]

A picture would help.

[rollinsrods]

Here's some pics...I hope

 

 

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[/url]">http://http://s90.photobucket.com/user/121977/media/Ratsun%20vent%20line%201.jpg.html'>

[rollinsrods]

BTW-Photobucket tutorial is excellent!

[datzenmike]

That is the gas tank vent for use with a charcoal canister.

 

The canister has three hoses.  One to the gas tank vent. Two to the intake although it has a small restriction so it is not seen as a vacuum leak. Three to the vacuum advance on the distributor.

[rollinsrods]

Is this something to pick up at the salvage yard, or should I try aftermarket?  How should I plumb the lines off it into a Weber 32/36 set up?

[ggzilla]

It doesn't connect to the carburetor or air cleaner, so no worries. One hose to the gas tank vent. One to the intake . One to the vacuum advance on the distributor. Don't worry about the "small restriction" as its built into the canister valve. This is all covered in a factory service manual or a chiltons or clymers, with diagrams and photos even.

 

Charcoal canister I've never seen aftermarket. Get a nice used one (I got a new looking unit from a 1986 sentra and it worked on my pickup) OR buy a new one from Nissan.

[rollinsrods]

So should I plug the vacuum fitting on my intake and just run straight to the dizzy off the canister?  Anyone know the interchange on a charcoal canister for this?  Restriction stay pretty constant, or am I looking at huge differences between Nissans?  I always question the Chilton manuals.  I'd rather get correct info from people (without my terminology hickup and lack of photos).  I've run into a ton of major mistakes in those manuals over the years and factory manuals are $$$.  I have a Chilton for my truck but half the stuff seems overly generalized and the other half is missing plenty of info.  Thanks for all the help, guys!

[ggzilla]

Factory manuals can be found for $20 on eBay. Or even less. I paid only $5 for my dozen or Datsun factory service manuals. Start looking. As low as $20 on amazon.com the worlds largest bookstore.

[datzenmike]

You need the vacuum advance for the distributor left working as is. Just connect the canister into it. This is the signal needed to tell the canister to 'purge' it's stored contents. All this does is open a valve and allow the intake vacuum to pull the fumes out of the canister.