74 620 gas shoots out of filler neck during fillup

[Cardinal Grammeter]

I sometimes forget, stick the nozzle in the neck and squeeze the lever all the way - then I sometimes get gas all over me.

 

The gas shoots out of the neck like I had the filler nozzle pointed out of the neck.

 

There is a big difference if I put the nozzle against the neck ID in different places and also with different nozzle angles - but I never remember which way works the best.

 

Is this common?  because it is very frustrating.

 

I did put a new filler neck hose on it - a nice Gates universal with a 45* bend.  It was a little oversize maybe 1/8"

 

Thinking about it, perhaps the clamp at the tank, is too far down the tank tube so that the hose is actually pulled away from the end of the tube - the step messes up the gas trying to slide down the ID into the neck....

 

... just thought of a way to check this:  put another hose clamp at or just beyond the tank tube end and see if that solves the problem.

 

But then it's still a legitimate question if these trucks are prone to this projectile spillage during fillup?

 

Note:  none of the venting tubes are connected correctly and the monkey's that worked on this truck (they couldn't afford apes) could have done all sorts of mischief on top of the tank.

[Dolomite]

It's normal for any datsun with a leaded fuel filler neck, there's a fix using parts from newer vehicles.

[Cardinal Grammeter]

Wow, that must be #2 on the list where #1 is their hoods fly open.

 

Oh but wait, it's a 1974 truck and there is no leaded fuel baffle in the filler neck - I know because I had to remove it to install the hose.

[Rick-rat]

Hook up your vent line, will lessen this, fill at slower speed with nozzle, mine doesn't have this problem and hood stays closed

[datzenmike]

My 74 710 has never had this happen and it has the old style filler. On my Canby trip I topped up at about 1/2 to 3/4 tank so at about 8 gallons every top up and up over 110 gallons that's at least 14 different gas nozzles.

[got ban]

You did make sure you're putting the right end of the nozzle in the hole right?

[Cardinal Grammeter]

All the small fittings on top of the tank are butchered.  At least one not connected at all and hard to say what the other(s) are doing.

 

It seems obvious to me that there is something wrong, since you can't even come close to "full throttle" filling.

[datzenmike]

As the gas goes in air rushes out the filler.... normally. There is a port on the filler nozzle that senses a venturi effect vacuum signal. As this changes as the fill pipe fills with gas the handle is released to shut the fuel off.

 

If you have an unsealed tank or filler pipe this is likely the problem.

[Cardinal Grammeter]

Don't know what you mean by "unsealed."

 

It doesn't take a lot of air bleed in a gas can to get it to pour without gulping.  And I know I have one unconnected nipple on the top of the tank - so that should be a good vent.  However, can't say much about anything else.

 

I've got to try the hose clamp experiment.  The rubber fillter hose is 1/8" too large and if the internal walls of the fillter tube are not smooth, the gas will not swirl smoothly into the tank.  If the end of the tank fillter nipple is pulled away from the larger filler hose, it could cause the gas flow to separate from the wall - and if it does this all the way around, it might just create a solid slug of gas in the tube which would get blown out by the outrushing air.

[datzenmike]

You're over thinking it. Swirling only slows it down. There should be a vent pipe that empties air from the tank up to where the gas nozzle is. Gas just falls down into the tank and does not have the air trying to get out the same filler hose. 

 

If you don't have this, air will burp out throwing the gas ahead of it.

[Rick-rat]

He has to overthink everything, the nature of engineers. When I replaced my hose I just used a straight piece of hose and it had a slight kink in it to fit. Never had a problem with it. And it was the right size hose, not one that was 1/8 inch larger

[Cardinal Grammeter]

OK, sounds like the answer is, "No, it shouldn't be doing that."

 

datzenmike:

 

The tank vents and evap were seriously molested.  Throughout the truck, any emission control stuff was ripped out, broken/sawed off, or actually removed. 

• They removed the evap/reservoir tank from up in the wheel well
• There is a 90* hose barb on top of the tank that is unconnected - it can be seen looking above the frame.
• There is a length of steel tubing flopping around on top of the tank that is connected with rubber hose to another 90* tank hose barb (I Think.)   I think it is the evap line tube that that they cut off???
• That makes 2 "vents" - isn't there a 3rd?  I thought there was some kind of actual vent that went vertically upward from... not sure - only pic is from the parts manual illustration.  If they blocked that off, yes, I'd have this problem.
• I can't remember if there was a hose barb on the filler neck.  Thinking about it, there may have been a 90* near the cap.  But if there was, it's unconnected.

The tank has lots of rust (my Hastings clear bowl fuel filter has lots of rust sediment) :should be dropped and chip stone tumbled on a cement mixer to get all the rust out of it. 

 

 

 

Rick-rat:

 

Where did you get that hose?

 

I couldn't buy the right sized hose - Gates doesn't make metric sizes.  And even if I could have bought metric hose, the neck OD was not close to any reasonable metric dimension.  A bastard size?

 

But I did not use a straight hose, I got one with 45* bend in it - and this bend was a little more than I needed.  Maybe the 45* bend is upsetting the flow?

[Rick-rat]

I believe that the hose was from NAPA, don't remember what size it was. Did this several years ago

[Cardinal Grammeter]

Is it possible the 45* bend could be an "obstruction" to smooth flow?

 

NOTE:  did part of the experiment regarding the hose being 1/8" larger than the neck/tank:  since it was difficult to clamp the hose down on the end of the tank neck, I did it on the fillter neck and eliminated the "ski jump."

[Cardinal Grammeter]

SOLVED  ??  (NOTE:  The old emojis were better)

It was the new hose with the molded bend - the bend was acting like a "ski jump" and launching the fuel stream up into the venting air stream.

 

The OE hose I removed was straight although the tank neck and filler neck were not co-linear.  So I decided to get a hose with the proper bend in it.

 

My solution was to keep cutting the bend back, try the fit and if there was any indication of a localized change to the flow path, remove and cut back some more.

 

I ended up with a straight segment from tank to filler necks with a little bend left on the tank end that made for a better hose clamping.

 

Today it took FULL THROTTLE at the gas pump.

 

Finally.....

Edited October 27, 2018 by Cardinal Grammeter