suspect fuel supply on an SC

[Peter Roberts]

I am having some trouble setting the car up following my restoration.
Whilst running to set the carbs the car it operates ok for a while but suddenly stops. Taking the fuel supply line off the petrol pump shows its dry.
I have fuel but the tank is not full, the pump is working and all the rubber fuel lines are brand new. I also rebuilt the fuel cock and the petrol pump.]
If i blow down the fuel line from the pump inlet i can here it bubbling in the tank so no restriction. If i pressurise the fuel tank by blowing into it then i get fuel to the pump.
I have checked levels and the bottom of the fuel tank is 2" below the petrol pipe that goes over the axle into the engine bay. This explains why i cannot get petrol out of the pump supply hose without pressurising the tank.
Firstly are these levels correct as i cannot do anything about it.
If it is correct then petrol can only be supplied by pump suction when the fuel tank has only got a gallon or so of fuel..
Anyone got any thoughts on this please.

[Ashley James]

I think fuel almost reaches the carbs by gravity. Have you tried cranking the engine with the fuel pipe emptying into a glass container to make sure it’s working okay.

I’d have thought the points gap being to tight or the timing not being right statically along with sticking bob weights might be a better guess.

[Peter Roberts]

I have sorted the tickover, high revs problem and am just trying to do the final mixture setting to get it spot on when this issue arose.
I have tested the pump and it works ok but to make sure that there was not perhaps a small hole in the diaphragm i rebuilt it this morning and have tested it.
I just find it strange that the tank does not give a gravity feed when lower on fuel. I cannot drop the suppl;y pipe as it passes through the tinware on the engine.

[roy mawbey]

Peter,

Fuel does come by gravity to the fuel pump. The pump should deliver it to the carbs. However of course and its so easy to forget, the petcock. If its just in the position 'on ' and the petrol level is really low say about a gallon then the 'reserve' position must be set. The delivery pipes inside the tank are at different levels!!

A while ago I was running the car down the road and suddenly a pop and a bang and the car started to stutter.Only after a ten seconds or so did I have the sense to move the handle to reserve. I forgot I was so low on fuel, the fuel needle was a way under quarter tank.

Roy

[Peter Roberts]

I am aware of the pet cock function and am on reserve as I did not want to put too much fuel in whilst commissioning.
I have the car on a lift so can get underneath. I have measured to the bottom of the tank and to the highest point of the fuel pipe going through the tinware and the tank is a full 2 inches lower than the pipe so unless the fuel tank is fairly full it will not feed the pump by gravity. That means pump suction is the only way that fuel will get to the pump

[Nine One One]

Floats not stuck in the carbs, thus restricting passage of fuel to the engine? Coil over heating? Points gap all correct?

[Peter Roberts]

No This is purely a fuel supply problem. When engine stops i take off the pump supply pipe to the pump and there is no fuel there. I blow into the fuel tank and fuel come through the pipe. Put pipe back on the pump and it fires up as soon as the the carbs are full.
I run it off and on for some time whilst setting up the carbs and then i get the same problem again when the engine runs out of fuel. Take off the fuel pipe to the pump again and nothing comes out.
I know the pipe is clear because i have blown back through it and i can here it bubbling in the tank.
Its almost as if when the engine is stopped some fuel leaks back to the tank as the supply pipe goes above the level in the tank causing an air lock and then the pump will not suck enough to pull it through again

[Nine One One]

One that has cropped up before...........the actual plunger for the fuel pump is not too short is it, there are different lengths.
The initial pumping is sufficient to get fuel to start the engine, but can not keep up with the flow once the engine is running.
If there is no fuel in the pipe, its either a feed problem, or the pump is not working as it should, There was an article somewhere about the diaphragm spring not being correct in some kits.
How about gravity feeding the pump itself from a container in the engine bay to the pump, and see if it runs ok then.

If it does, its a problem with the feed from the tank.

If it does not its a problem with the pump.

Its just a case of dialling out which one is the issue

Ian

[Ignatzcatz]

I think you may have unwittingly found your problem in your first post when you stated "if I pressurise the fuel tank . . ". I took a cue from a friends BT5 which was always maintained by Andy Prill who recommended, then had fitted an electric fuel pump fitted just to prime the carbs for easier starting. I took the same route and fitted a small electric pump by the tank onto the K member, so it is unseen, for the 356 police. But then I went the whole hog and fitted a big V8 size Carter pump in the engine bay and just made a blanking plate to cover the hole where the old mechanical fuel pump was fitted. The result was instant starting and zero fuel supply problems. Whilst many folks will say they never had any problems with the standard pump, I still believe it's quite a big ask of a little pump to suck petrol along a fairly tortuous route then fill up the float bowls of a pair of rather large carburettors.

[wildtexas]

Blocked fuel breather on the tank? Next time it dies on you take off the fuel filler cap and see if it sucks air in?

[Peter Roberts]

Definitely not a blocked breather as this has all been replaced during the Resto and we are not looking at a lot of fuel use between the problem reoccurring. The car is on ramps and I am only trying to set up the carbs so tick over and occasionally reving the engine.
I have read up about the electric fuel pump route but would rather not do that. Car has run for years without a problem . This Has arisen during my restoration.
Tomorrow I will try to measure the discharge from the pump to ensure it’s adequate.

[PeterK]

Given that the issue is post resto, any chance of something as simple as a kink in the fuel line restricting flow ?


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[POR68]

Is there something in the fuel line that moves when you blow through the line towards the tank and then when running, moves back causing a restriction? I once had a piece of straw in the fuel line that did that. Took me weeks to find it. Also you haven't mentioned any (additional) filters attached?

[Peter Roberts]

Get the point about something in the line however the tank was removed and pet cock stripped I found nothing in the filters to make me concerned. Tank was checked internally for rust and debris but was extremely clean but was blown out anyway. Petcock rebuilt with new filters. All rubber hoses replaced with new.,
If I blow down the fuel supply line with my mouth it is not difficult and I can here air bubbling in the tank which suggests it’s clear

[POR68]

True Peter. The hard line in the tunnel is clear then. You can blow through easily BOTH ways? My problem was I could blow through one way - to the tank - but the other way caused the impediment to lodge like a small valve. Seems you have checked all the possibilities otherwise. The mechanical fuel pump is working as you say ... If gravity is involved, does the fuel cap seal completely and create a vacuum that the pump can't overcome? Stupid question I guess.

More importantly, on the fuel pump, you checked the diaphragm. Is shaft seating correctly? That is, is the pump shaft seal sealing correctly? If not, it may be permitting leakage back to the tank instead of pressure to the carbs.

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