Lotus Elan

Elan +2 fuel tank

PostPost by: rdssdi » Fri May 31, 2013 4:10 pm

I am in the process of installing my +2 fuel tank. It is a custom unit beautifully fabricated by Axminster Specialist Panels in the UK. I have disassembled the fuel system to inspect and clean as necessary as I will be installing freshly rebuilt carbs (ZS 175) and I do not want any problems. I found no signs of corrosion nor any sediment.

I have used this time to analyze the fuel gauge sender as I never can get the gauge to read full. There is plenty of room for the float arm to travel within the tank and when wired and energized the gauge reads empty when at one extreme of float travel and full at the opposite end of travel. I am convinced that my problem lies with the fact that the tank is never full. I suspected this as once the fuel level passes the filler neck pipe entry position the fuel can only enter the tank when the fuel level in the filler neck is above the tank fuel level. It is a tedious task and no matter how long I coax fuel into the tank I cannot get a full reading.

Has anyone else with a +2 have a similar difficulty?

Bob
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PostPost by: PeterK » Fri May 31, 2013 4:52 pm

If you bent the float arm slightly, then it would read full earlier (as full as practically possible)
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PostPost by: cal44 » Sat Jun 01, 2013 1:58 am

Bob,
what are you doing for a fuel line? Going to steel? and what Peter said.
The Axminster tank is on my " work of art auto part " bucket list.

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PostPost by: elanman999 » Sat Jun 01, 2013 10:34 am

Bob,
A +2 is very slow to fill when the fuel level is above the tank inlet pipe. When it is full you can see the fuel in the filler neck, approx 1 to 2 ins from the top.
Are the tank vent pipes large enough and clear?
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John
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PostPost by: rdssdi » Sat Jun 01, 2013 12:48 pm

I used aeroquip braided line from tank to fuel filter to pump. The filter is an alloy cased Earls filter mounted under the car close to the tank. At some time in the future I may change to a hard line. I am running a Spyder chassis and I would have to give some thought to the hard fuel line size and route.

The Axminster tank is a work of art. I had mine made slightly lower to allow room for AN roll over vents. These ball valves are common. I then used AN 90deg. elbows to attach to the roll over ball valves with a pressure discriminating valve placed in line. While these valves from Newtown Equipment are designed to only allow air to pass above and below a pre set pressure, I felt they inhibited fuel tank filling. I was hoping they would function seamlessly as the tank vent lines are a source of fuel vapor loss and a smelly garage. I may reconnect them and see how they work.

The vent lines are -6. Two -6 lines should be sufficient to allow the tank to fill.
The new fuel filler neck rubber elbow will be delivered on Monday. I will begin reinstallation of the tank.
Bob
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PostPost by: elanman999 » Sat Jun 01, 2013 3:03 pm

Bob,
-6 is a tad smaller than the original so will not help. However I would think the main problem is in the roll over vent and other valves. Can you try it with only the -6 pipes on? Also -6 fittings have a lot smaller hole in them than -6 pipe, could the fittings be enlarged?
But hay it's +2 so a smelly garage goes with the car. :)
Talking of smelly garage what pipe are you using, PTFE or rubber?
cheers
John
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PostPost by: stugilmour » Sun Jun 02, 2013 3:48 pm

Bob, I have the same setup (Spyder frame, Axminster tank, filter by tank outlet, and electric pump by the right rear wheel well). Fuel filling is slower for the last part of the tank, but acceptable. Slight fuel odour does occur inside the trunk; will be nipping up a few of the clamps. There is not the extreme garage odour I had with the stock setup, which was replaced.

I used the method of running a large diameter vent hose back to the filler neck. This method is shown in an article from the Club Lotus magazine. It vents vapour and some liquid fuel back to the neck during filling. With the filler lid shut this vent hose does not allow vapour to escape the system. I blocked the pin hole vent in my replacement fuel cap; not sure if the stock caps had this pinhole but it is not required with the vent hoses over the rear window. Before the pin hole was blocked I had fuel slopping out of the lid on cornering or from expansion when the car sat in the direct sun.

The vent line over the rear window is much smaller in diameter. It is sufficient to vent the tank during running, but way too small to vent during filling. The small diameter line is tee'd in to the large diameter line running between the tank vent nipples and over to the fuel filler neck. I only ran one small diameter vent line rather than the stock two line arrangement. When we were discussing the Plus 2 venting in an older thread, a poster suggested the small diameter vent line prevents a vapour siphon happening; makes sense to me. At any rate, the small diameter vent on my car prevents the smelly garage issue well enough that I think I will be able to store the car over that my In-Law's place. :D

For the gauge, I purchased a new sender from Axminster and installed it. Mine also does not go to the full reading even when the tank is brimming, but works fine over the rest of the range. Critically the low fuel light and gauge readings are very consistent at the lower range. I have decided to just live with it. To tune yours up before the tank and sender is in place try the sender over its range using the car wiring to see if the gauge works. I think mine went to full when I did this, so bending the float rod a bit may fix things up. Might change the low range reading a bit though. Any additional resistance in the wiring will limit the full reading. I don't have the resistance readings of the sender to hand, but from memory I think it was about 20 ohms at the full reading, so even slightly increased resistance in the wiring can cause an issue.

HTH
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PostPost by: rdssdi » Mon Jun 03, 2013 8:55 pm

I received the new filler neck to tank rubber elbow. I will be finishing the tank install this week. I have two vent lines that do not run around the window opening. I had two vent roll over shut off ball valves installed by Axminster. I do not understand why a large vent hose running to the filler neck will allow faster fills. The tank vent openings and their respective hoses remain the same inside diameter therefore flowing the same amount of air. I will adjust the gauge sender arm to get as close to a full reading while maintaing an accurate empty reading. If I mark the approximate level of "full" for the float I can get an idea of the number of gallons held by using the gauge reading. Assuming the tank will accept that much fuel for a "full" reading before filling is limited by the filler neck design.

I will post my results.

Bob
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PostPost by: stugilmour » Mon Jun 03, 2013 9:53 pm

I guess I might not have been very clear Bob.

The vent line size with the hose routed to the filler neck is similar to the vents run in the conventional manner over the window. You are correct, filling speed issues are probably similar with both configurations, I like the routing to the filler neck though as it will burp liquid fuel back to the filler neck and clear the vent during filling. Not sure how that works with the stock configuration; my stock lines were well past their best anyway.

The big advantage with the filler neck configuration is it allows the use of a smaller vent line, which only has to be sized for running conditions. This greatly reduces the garage odours. I don't get any odour outside the car any more; with the stock configuration it was pretty bad.

Anyway, sounds like you are taking a different approach.

HTH
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