Fuel line question

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Dryad
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Fuel line question

Postby Dryad » Tue Jun 07, 2016 8:52 pm

I have just fitted a new fuel line, but I think air is getting in at the tank end because the pump is pumping furiously. I've tightened the brass screw-in connector to the tank as tight as I dare, but it already takes a fair amount of force to turn it and I don't want to damage the thread. I tried putting a thin layer of grease on the thread, which has helped to turn it, but I still think air is getting in. Any recommendations? The fast clicking fuel pump is getting on my nerves! :roll:


bmcecosse
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Re: Fuel line question

Postby bmcecosse » Tue Jun 07, 2016 9:55 pm

Does fuel leak out anywhere when the pump is not running?
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Dryad
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Re: Fuel line question

Postby Dryad » Tue Jun 07, 2016 10:08 pm

There was a slight seepage, but that stopped when I tighted it a bit further. I thought of using some plumbers' PTFE tape but wasn't sure whether it would stand up to being in contact with petrol.


bmcecosse
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Re: Fuel line question

Postby bmcecosse » Tue Jun 07, 2016 11:12 pm

If fuel doesn't leak out, then air shouldn't be able to get in. Is there enough fuel in then tank to cover the pick up ???
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Dryad
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Re: Fuel line question

Postby Dryad » Wed Jun 08, 2016 7:01 am

There's around a gallon or so, but I could try putting more in. I'll let you know what happens.


oliver90owner
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Re: Fuel line question

Postby oliver90owner » Wed Jun 08, 2016 8:42 am

Please give more details of the new pipe. There are clearly two connections but may be more. The highest negative pressure will be at the pump inlet. Are you sure the connection(s) are airtight at the pump? And, yes, air can easily leak in at this point without fuel leaking out (always a negative pressure due to syphoning back to the tank).

bmcecosse
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Re: Fuel line question

Postby bmcecosse » Wed Jun 08, 2016 1:15 pm

The concern was for air getting in at the tank connection. 1 Gallon maybe not enough to cover the inlet filter inside the tank - add another and see what happens.
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oliver90owner
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Re: Fuel line question

Postby oliver90owner » Thu Jun 09, 2016 7:36 am

The concern was for air getting in at the tank connection. 

Not so. While I agree with the fuel level comment, the poster only 'thought' it was the tank connection - but there is also at least one other connection. As I said, air can be leaking in at the pump end without any fuel leaking out. All relevant information is required to diagnose the problem. Concentrating on the tank end (fuel level and tightness of the connector) will not solve the problem if it is elsewhere! Closing one's eyes to other possibilities, until forced to open them, may not be the way to get a speedy resolution.

Dryad
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Re: Fuel line question

Postby Dryad » Thu Jun 09, 2016 12:27 pm

Well I put another gallon in and...no change. I should have said before that I initally fitted the new fuel line last year and had no problems, so I don't think it's the pump end. Air is obviously getting in the tank end, and I just wondered if anyone had any handy tips of creating an airtight seal, other than tightening the connector up so much that I damage the threads. Perhaps I'll just try and tighten it a bit further... :o


bmcecosse
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Re: Fuel line question

Postby bmcecosse » Thu Jun 09, 2016 1:04 pm

Well - I feel if petrol is not leaking out - air won't be going in. Maybe the filter inside the tank is blocked? Have you tried a pump flow test - to see how long it takes the pump to move 2 pints? And if you dip the delivery end under the surface, you will see if there are any air bubbles coming through. Take care obviously with open petrol and any possible sparks.....
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simmitc
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Re: Fuel line question

Postby simmitc » Thu Jun 09, 2016 6:06 pm

As above, is there fuel coming through the system at all? Disconnect the pipe from the pump and blow down it. Can you blow down it? Can you hear bubbling in the tank? Get an accomplice to listen for an air leak.

If I understand correctly, it all worked fine until you fitted the new fuel line, so the temptation must be to suspect the pipe as the changed item, but we do need the reuslts of Roy's suggestion above. My thinking is whether the pipe is blocked with a foreign body, or has the pick-up tube in the tank succumbed to old age and fallen off?

You can safely use PTFE tape on the threads of the connector. Did the pipe have the correct fitting soldered to the end when you bought it? i have seen new ones come out without the "nozzle", and that would certainly prevent it from sealing.

oliver90owner
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Re: Fuel line question

Postby oliver90owner » Fri Jun 10, 2016 12:41 am

As with allall compression plumbing fittings, the seal is metal to metal. The parallel threads are there to tighten the joint and not as a seal. Threaded seals use tapered threads and pipe tape (or hessian and boss white in the olde days).


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