Lotus Elan

Gas tank vent

PostPost by: frearther » Sun Jun 06, 2010 4:45 pm

I'm trying to solve a new fuel feed problem on my S2; looking at the tank, I'm stumped as to how it is vented to prevent airlock as the fuel level recedes. There is a pipe - apparently a vent pipe - about 1/4 inch wide mounted inside the filler pipe. The bottom protrudes into the fuel. The top is open, but it only opens into the filler pipe which is sealed from the atmosphere when the cap is closed. It looks like a closed system to me, but that wouldn't work. So I assume there is another vent somewhere that I'm overlooking.

Can anyone enlighten me (said he with embarrassment).
Art Frederick
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PostPost by: alan71 » Sun Jun 06, 2010 5:08 pm

The vent is in the filler cap, the small pipe is to let the air out while you are filling the tank.

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PostPost by: frearther » Sun Jun 06, 2010 6:36 pm

My filler cap is the "quick release" type. How do I find the vent to be sure it's not plugged?
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PostPost by: prezoom » Sun Jun 06, 2010 7:13 pm

Art,

My S2 is equipped exactly like yours, and the tank vents through the flip cap. If you want to check to see if the cap is plugged, remove the cap/tube and try to draw a vacuum from the bottom of the tube with the cap closed. You will have to plug the small tube, and draw through the large tube or just the opposite. If you have a MityVac, it may be easier to plug the large tube with some tape. You should not be able to draw a vacuum and hold it, with the cap vent.

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PostPost by: Robbie693 » Sun Jun 06, 2010 10:37 pm

frearther wrote:My filler cap is the "quick release" type. How do I find the vent to be sure it's not plugged?


There should be a hole in the sealing ring to breathe through. On the cap on my Plus 2 (sorry if these are different - I'm not sure what is fitted to S2's) there was a hole in each half of the sealing plate, 180 deg apart, top and bottom to vent to atmosphere.

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PostPost by: frearther » Mon Jun 07, 2010 11:17 am

Robbie, my cap is different - there are no holes in the sealing plate.

Rob, I'll do the check that you suggest. That sounds like a good way to find out whether or not my vent got plugged.

Thanks to all who helped.
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PostPost by: RotoFlexible » Tue Jun 08, 2010 6:01 pm

frearther wrote:Robbie, my cap is different - there are no holes in the sealing plate.

Rob, I'll do the check that you suggest. That sounds like a good way to find out whether or not my vent got plugged.

Thanks to all who helped.


I believe I've seen the hole in my sealing plate (also an S2). Ever since the tank was reconditioned (along with many other changes to the car), I have had occasional issues that seem related to fuel feed. They have just resurfaced. Has anyone ever experienced fuel feed problems that could be traced back to the cap vent?

An easy way to check this is to simply unlatch the cap when the problem occurs, and see if it goes away.
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PostPost by: frearther » Sun Jun 13, 2010 7:25 pm

I just finished a vacuum test on the filler tube assembly, and it does vent to the atmosphere. I used the Mighty Vac procedure since the fuel system was already partly disassembled before I even thought to check the vent. But since the vent works, I guess I have to look for gunk in the line somewhere. Rats! :cry:
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PostPost by: prezoom » Mon Jun 14, 2010 3:49 pm

Let us know what you find. On my last run, it looks like the DPO's having the fuel tank coated is now coming undone. Something is getting sucked up against the end of the tube in the tank and shutting off the flow. Have to shut off the electric pump and let the stuff fall off then restart the pump to get fuel back in the carbs. Will source a new place to get the tank cleaned and recoated.

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PostPost by: frearther » Mon Jun 14, 2010 5:34 pm

prezoom wrote:On my last run, it looks like the DPO's having the fuel tank coated is now coming undone.
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I'm awfully afraid that this is my problem, except that I'm the DPO :cry: :oops:
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PostPost by: Galwaylotus » Mon Jun 14, 2010 7:45 pm

frearther wrote:
prezoom wrote:On my last run, it looks like the DPO's having the fuel tank coated is now coming undone.
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I'm awfully afraid that this is my problem, except that I'm the DPO :cry: :oops:

Look on the bright side. You don't have to go far to give out to the guilty party!! :lol: :lol:
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