Slow Fuel Filling Solved

[lukeg]

I finally got my slow fuel filling issues resolved. I have seen other people mention this on here as a problem, so I thought I'd post up the solution.

The donor was a 1999 Miata (1.8), so it may be slightly different depending on the model year.

On the 1999 gas tank, there are two main hoses, one is a 1.5" hose for the fuel filler and the other (slightly above it) is a 5/8" hose for the tank vent. I think some people are incorrectly plumbing the vent hose into the fuel lines in some way. The vent hose MUST have an unrestricted ability to move air up and out of the tank as you fill it. If it is restricted in any way, it will cause the fill hose to back up and bubble. It would take me 10 minutes to fill the tank because it would back up with bubbles so bad. After routing the vent hose into the factory location at the top of the filler, I can now fill at full speed. WOOHOO!!!!

I have an aircraft style aluminum fuel filling cap and had a friend weld on an aluminum right angle barb from a cut down -AN fitting to run the vent hose properly to the side of the fuel filler similar to the factory location. I could not find a non-plastic fuel filler with a 5/8" barb for the vent, so I had no choice but to modify the one I already had.

A very similar fitting to the one I used as a vent bung on the fuel filler...
www.amazon.com/NOS-21928333-Black-Degrees-Hose/dp/B006JZ3I90/ref=sr_1_32

Hope this helps someone.

Cheers!





 

[freshp5]

You got any photo of how you do it

[lukeg]

I'll take some this weekend and post them up. It was a pain in the ass to figure it all out, but the way I did it ended up working out really well and looks great. I tried using the factory filler sticking out of the rear body work, but hated the look of it.

[freshp5]

That be great as the two mevster we have fill slow

[lukeg]

Okay, here is a very detailed explanation with some epic diagrams.

The parts I used are below.

Aircraft Style Fuel Filler
monstermarinestore.com/en/fuel-fills-fuel-systems/264-1-12-fuel-fill-billet-aircraft-style-.html

1.5" Stainless Fuel Hose Coupling
www.fillernecksupply.com/1-1-2-inch-fuel-filler-hose-joiner-coupling-stainless-steel/

Gates 1.5" 90 Degree Fuel Filler Elbow (you need two of these!)
www.fillernecksupply.com/gates-1-1-2-90-degree-fuel-filler-elbow-gates-24715-goodyear-59205/

5/8" Aluminum Right Angle Hose Barb Fitting
www.summitracing.com/parts/edl-8178/overview/

Couple Feet of 5/8" Fuel Hose from the auto parts store



I had a friend drill out the aircraft fuel filler so he could weld on the 5/8" barb. You'll need to cut down the threaded side of the barb so it doesn't stick out past the flange and still looks nice. Similar to the one in the image below for reference. Then have it welded on so it is facing down with the other main fuel line. Ideally the hole for the barb into the filler is above where the fuel nozzle will go when you fill the tank. A lot of air will be moving through it. Make sure you have enough room for the two hoses and clamps beside each other. Mine was super tight and both hoses barely fit.






Both right angle gates hoses will need to be cut down. It is going to take some measuring to get perfect and I highly recommend a second set of hands to help. The basic jist of it is in the image below. You want one right angle coming horizontally off the fuel tank into the coupler and the other right angle hose coming down vertically from the filler and attaching to the coupler. I mounted one hose with the coupler onto the tank and then had the other hose tightened onto the filler. Made it super easy to measure and refit and then attach when done. You can angle the hose clamps on the coupler to be facing down and there is just enough room to reach them and get them tight with the trunk lid on.




The key to being able to fill at full speed is allowing the air coming out of the 5/8" barb on the fuel tank to go up and out unrestricted. You need to run the 5/8" hose without kinks to the fuel filler. With the rear bodywork tilted up from your helper, you should be able to get the 5/8" hose coming from the filler barb to the tank. It is simple in theory, but a bit of a pain because you need someone to help hold the rear bodywork up while you fit all the hoses. Once done though, you should be able to fill at full speed with no issues.

Hope this helps some people. It was a bitch to get right finally, but slow filling sucks.

[clintavo]

I did this exact thing. A tapped vent to the same filler you have, running a hose to the stock vent location. It made zero difference with my slow fill. Wonder what I did differently to make it not work?

On a side note, I fill my tank very high, and noticed fuel seeping from the vent line where it meets the tank. I eliminated it, and sealed it up with resin. No more fuel smell in my garage.

[lukeg]

I noticed that if I don't put the gas filler nozzle below the vent hole in the fuel filler cap, it makes a mess and I can't fill at full speed. How far down is the vent hole in your cap? When I am filling it correctly it has a lot of air coming out of the tank that is being displaced. 

Maybe check for a kink in the hose with the bodywork on. Something has to be off. This fixed my slow filling problem immediately.

[lukeg]

Just reread your post. Did you epoxy shut the tank vent barb on top of the fuel inlet? The smaller hose barb on top in this image. If not, what exactly did you epoxy shut?

[clintavo]

It was leaking pretty bad, so I used vise grips to flatten the tank line, then sealed it.

My vent was tapped to the same height as yours. I wonder if there is something going on internally in the tank? I drove a few thousand miles with no bodywork, and the stock, long filler and vent line. I had to make a separate vent to make it fill even then. 

[lukeg]

Can you show me a pic of the line you epoxied shut and your setup with the bodywork off? Might be able to help better then.

Also, I would run the tank low in gas and reinstall the stock long filler with no bodywork. Then when you go to fill up, try popping off the vent hose and see if you can see/hear the air coming out of it as you fill (obviously don't fill to the top like this!). If no air comes out then you have an internal issue, clog, etc. Might even be worth it to open up the tank, but I don't know the details of what you can actually get to in the tank. There should be a VERY noticeable amount of air coming out of the vent hole as you fill.

If you are running essentially the same setup as me, then it should be working. Mine works perfectly.