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paulhide · Posted: Sun Jan 23, 2011 1:30 pm Post subject: Fuel Delivery

Someone has just phoned me and said that when the car is left for a few days the fuel in the pipe seems to return to the tank and it takes ages to pump the fuel back to start the car.
Anyone got any ideas why this may occur?
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johnboy · Posted: Sun Jan 23, 2011 11:18 pm Post subject:

Is it parked on a hill Laughing

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paulhide · Posted: Mon Jan 24, 2011 11:14 am Post subject:

Thanks John, very helpful Exclamation

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Ian M · Posted: Mon Jan 24, 2011 10:17 pm Post subject:

JeremyC · Posted: Tue Jan 25, 2011 10:14 am Post subject:

Probably a small leak somewhere.

If the system is completely sealed then the 'vacuum' keeps the fuel where it is. If there is a leak somewhere then air can get in and gravity tends to make the fuel sink back down into the tank (or out of the leak depending where it is).
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Oggie · Posted: Tue Jan 25, 2011 11:30 am Post subject:

Surely this is perfectly normal, if the tank has a breather pipe the vacuum would disappear after a min or 2. It always takes 3-5 seconds to start my car and I use a facet redtop electrical fuel pump so fuel to the engine is almost instant!.
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JeremyC · Posted: Tue Jan 25, 2011 11:54 am Post subject:

If I stand at the top of som step ladders and suck water from a bucket up a hose pipe and then put my thumb over the top the water will stay in the pipe indefinitely even though the bucket is vented. Atmospheric pressure can get in the the bottom of the pipe but not the top (because of my thumb) and the pressure from below keeps the water in.

If I relax my thumb and let a little bit of atmospheric pressure in at the top then the water will slowly run out.
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Oggie · Posted: Tue Jan 25, 2011 6:25 pm Post subject:

Paul do you know of the fuelling type injection or carbs?. Jeremy I see what your saying but when the car is not running the pressure from the pump electrical or mechanical would eventually relax the vacuum.
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paulhide · Posted: Tue Jan 25, 2011 7:58 pm Post subject:

It's actually a 1350 twin carb Sud which is only used at the weekends. The guy is having to start for ages before any fuel finds its way to the carbs.
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Oggie · Posted: Wed Jan 26, 2011 9:51 am Post subject:

Sounds like its the diafram in the pump.
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paulhide · Posted: Wed Jan 26, 2011 3:59 pm Post subject:

Wouldn't it run bad if that were the case?
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Ian M · Posted: Wed Jan 26, 2011 7:20 pm Post subject:

So if its a twin carb there must be fuel in the float chambers and therefore I would expect the engine to initially fire and then start drawing fuel in.
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Oggie · Posted: Fri Jan 28, 2011 4:31 pm Post subject:

The problem with carb 33s is the fuel tends to evaporate in the carbs if you use an aftermarket air filter, a very common fault with the boxer config.
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