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Fuel Starvation
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Spanner5511



Joined: 10 May 2013
Posts: 7

PostPosted: Sat Jul 05, 2014 10:10 am    Post subject: Fuel Starvation Reply with quote

I usually use my Ford side valve 10HP only at weekends. When I try to start it there is no fuel present at the carb.

In-line glass filter is clean and clear.

It has a new mechanical fuel pump as per original design.

My thoughts:

Pump diaphram?

Too much pressure in tank?

Anyone else any ideas or experience of this?
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Penman



Joined: 23 Nov 2007
Posts: 4751
Location: Swindon, Wilts.

PostPosted: Sat Jul 05, 2014 12:04 pm    Post subject: Reply with quote

Hi
Is the glass filter emptying, or is it just losing fuel between there the pump and the carb
How about the one way valves in the pump just letting the fuel seep back towards the tank.
Is there a blocked breather for the tank?
A bit of suction from the tank could then pull the fuel backwards.
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colwyn500



Joined: 21 Oct 2012
Posts: 1745
Location: Nairn, Scotland

PostPosted: Sat Jul 05, 2014 2:17 pm    Post subject: Reply with quote

I have always had that issue on my Austin 10 and thought it normal. I assumed that the tendency of the carb and pump to drain back fuel was the reason why older cars always had the hand priming lever.
In a week you might lose the carb fuel through evaporation and leakage.
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colwyn500



Joined: 21 Oct 2012
Posts: 1745
Location: Nairn, Scotland

PostPosted: Sat Jul 05, 2014 2:18 pm    Post subject: Reply with quote

I have always had that issue on my Austin 10 and thought it normal. I assumed that the tendency of the carb and pump to drain back fuel was the reason why older cars always had the hand priming lever.
In a week you might lose the carb fuel through evaporation and leakage.
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Spanner5511



Joined: 10 May 2013
Posts: 7

PostPosted: Sat Jul 05, 2014 4:12 pm    Post subject: Reply with quote

I think you are looking in the right direction Penman. The pump is letting the fuel drain backwards which could well be a blocked breather. The glass filter certainly empties somehow.

Can't see it being evaporation, as the garage is really cool even when the outside temp is high. Even allowing for a hot engine, this is new in that it did not happen until recently.

Will be checking for any breather in the tank which may be blocked.
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D4B



Joined: 28 Dec 2010
Posts: 2083
Location: Hampshire UK

PostPosted: Sat Jul 05, 2014 4:20 pm    Post subject: Reply with quote

Spanner5511 wrote:
I think you are looking in the right direction Penman. The pump is letting the fuel drain backwards which could well be a blocked breather. The glass filter certainly empties somehow.

Can't see it being evaporation, as the garage is really cool even when the outside temp is high. Even allowing for a hot engine, this is new in that it did not happen until recently.

Will be checking for any breather in the tank which may be blocked.


Surely this could be proved or disproved by simply running the engine without the fuel filler cap on?
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Sat Jul 05, 2014 5:48 pm    Post subject: Reply with quote

If the carb. is higher than the petrol tank then fuel will WANT to drain back by gravity. But it can only do that if the non-return valves in the pump leak. And if they do it is probably only a matter of time to when delivery is compromised when running, Which will probably show up first as fuel starvation climbing a longish hill.
Jim.
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Spanner5511



Joined: 10 May 2013
Posts: 7

PostPosted: Sat Jul 05, 2014 6:31 pm    Post subject: Reply with quote

Surely this could be proved or disproved by simply running the engine without the fuel filler cap on?[/quote]

Engine runs fine with the fuel cap on. It is only when it has been parked for more than a couple of days that there is a problem with fuel starvation when trying to start the car.
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Spanner5511



Joined: 10 May 2013
Posts: 7

PostPosted: Sat Jul 05, 2014 6:34 pm    Post subject: Reply with quote

Jim.Walker wrote:
If the carb. is higher than the petrol tank then fuel will WANT to drain back by gravity. But it can only do that if the non-return valves in the pump leak. And if they do it is probably only a matter of time to when delivery is compromised when running, Which will probably show up first as fuel starvation climbing a longish hill.
Jim.


I thought so too, but it is a brand new pump . Maybe 400/500 miles and less than 12 months old.
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Sat Jul 05, 2014 6:41 pm    Post subject: Reply with quote

Spanner5511 wrote:
Jim.Walker wrote:
If the carb. is higher than the petrol tank then fuel will WANT to drain back by gravity. But it can only do that if the non-return valves in the pump leak. And if they do it is probably only a matter of time to when delivery is compromised when running, Which will probably show up first as fuel starvation climbing a longish hill.
Jim.


I thought so too, but it is a brand new pump . Maybe 400/500 miles and less than 12 months old.


Do we always accept that "new" means OK?
A pressure gauge temporarily installed on the delivery pipe to the carburetter will show pressure when the pump is primed (generally only about 2 or 3p.s.i. but different makes vary.
If the pump valves are OK the pressure will hold. If it falls.............? Well it could be due to dirt - but.............?
Any variation in delivery pressure is down to the strength of the delivery spring in the pump
Jim.

PS. You mentioned Diaphragm. Of course if that is leaking any fuel leaking through it will drain into the sump and smelling the sump oil will give that away. And it would still need a faulty delivery valve for the petrol to drain back from the carb.
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norustplease



Joined: 11 Apr 2011
Posts: 779
Location: Lancashire

PostPosted: Wed Jul 09, 2014 6:11 pm    Post subject: Reply with quote

What does your handbook say? My Austin 10 handbook is quite clear that after a few days, you should prime with the pump lever, to avoid having to crank for a long time when cold starting. It does make a difference and I suspect that the float chamber may well evaporate sufficiently to need freshening up after a week of idleness.
Incidentally, on most carbs the fuel feed is at the top of the float chamber. When the car is idle, gravity can only drain the fuel pipe. The condition of the non return valve in the pump only impacts marginally.
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Phil - Nottingham



Joined: 01 Jan 2008
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Location: Nottingham

PostPosted: Wed Jul 09, 2014 6:54 pm    Post subject: Reply with quote

Even our 1938 Rover 16 (P2) says priming is required and I do the same on our S2 and S3 LR's if left for a week or 2. Instant start then
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