Fuel vanishing from carbs?

[Leo Dolman]

Hi all,

 

I am having an issue with my Herald, the car runs fine but when it comes to starting the car after it has been left for a week or so, I am finding that there is no fuel left in the carbs (I have twin SUs fitted).  Once I have refilled them and sucked fuel back through the pipes again, the car then runs without issues.  

 

Do any of you have any idea as to why the carbs are draining fuel when the car is stopped?

 

or have any suggestions on how I can fix the issue so I don't have to have a mouth full of fuel every time I want to run the car?

 

 

My fuel system is arranged:

Tank>hose>fuel pump(mechanical)>hose>fuel filter>hose>carb1>hose>carb2

 

Any help would be much appreciated.

[AidanT]

Hi

 

I always thought this was simply due to evaporation of the fuel. I have to crank mine for a good few seconds before fuel arrives and it fires up, or if the battery is a bit flat I use the manual pump on the bottom of the fuel pump to push fuel in to the SU's. I of course stand to be corrected by those with more knowledge

 

Aidan

[Colin Lindsay]

If the fuel isn't leaking out of the bottom of the carbs then it's running back down the fuel line and having to be primed again before starting - this is why some older pumps have a priming handle so you can pump the fuel manually before cranking the starter. How old is your fuel pump? Perished valves may allow the fuel to drain back faster than normal; try another pump and see if it improves. I don't know if there's an in-line non-return valve available anywhere but cranking on full choke (short bursts of the starter) should get the fuel back to the carbs although as Aidan says after a few seconds. 

[Pete Lewis]

my view is its leaking somewhere under where the jet tube fits in the bowl,  what ever drains back to the tank  cant suck fuel from the chambers as the float valve is way above the fuel level..

 

depends on which spitfire tank you have but   many normally gravity feed the pump or syphon  to the pump 

anyone who's pulled the feed from the pump will find it flows  until corked up.

 

it does evaporate off but it should keep a full float level for a week or so without problems 

 

if the bowls are empty its leaking somewhere

 

many wont start when left problems are down to lack of choke, it wont fire till you  crank enough to get build up in the manifold 

and then away it goes ,  

 

Pete

[Leo Dolman]

Thanks for your help, the fuel pump is about 5 years old, the carbs where refurbished within the last 12 months. I will go out an check for leaks when the weather improves.

 

Would fitting an electric fuel pump by the fuel tank make starting the car easier?

[dougbgt6]

If there's a leak, anywhere, you can smell it. Been there, got that T shirt!  But If you've left it over winter you won't be in it to smell it and the smell will be gone by spring.   I guess once you've got it running then you'll be able to sniff it out.

[Pete Lewis]

If you fit an electric pump it must be max 2.5psi or you will overload the float

 

and they realy need an inertia switch to cut it off if theres afree flow leak or get an impact

 

but yes they priime as soon as switched on.

 

pete

[Steve C]

My car also "dries out" in storage over winter, and I used to flatten the battery trying to get fuel back up to the carbs. Modern high-ethyl level unleaded is incredibly volatile. You only have to see how fast it vanishes if you spill a bit filling the lawnmower!

 

My preferred method is an electric pump on a board, which sits on the front top wishbone, with a couple of croc clips to connect it to the battery and two lengths of rubber fuel pipe, one ending in a short piece of copper fuel tube. I split the fuel line on the outboard side of the mechanical pump, and connect in the electric pump and draw the (fresh) fuel through. I use the same rig to empty the tank before I put the car away in Autumn, putting old fuel in the modern, and always put in fresh Shell V-power for the spring start-up). It then takes only a few cranks to fire her up with a bit of choke, and it's off to the petrol station for a few gallons more of V-Power for the first events of the season.

 

I suppose the real answer it to use the car more, but it is a bit chilly in winter for my old bones in a convertible. As to electric pumps, to each their own, but for me, been there, got that T shirt, and more hassle than it was worth.

 

Regards

 

Steve C

[Steve P]

My Vitesse started doing this recently,it already has a Facet electric pump.I use it all year round but,If left for over a few days it takes an age to start,definitely fuel related as it fires in stages as more fuel gets to the plugs on cranking.

 

This has only started since i changed the exhaust manifold,maybe coincidence.

I am going to check all the braided fuel lines and replace them as some seem spongy to me..maybe gone porous internally due to ethanol?

Steve

[JohnD]

It's them garage pixies, petrolheads the lot of 'em.

 

Leave bowl of milk out.

 

Or buy an electric fuel pump.

John

[AidanT]

I would like to fit an in-line filter with a non-return valve to eliminate any drain back, but aprate from a few mm of hose near the T piece split for each carb, its all copper pipe all the way back to the pump. Probably specific to the Mk1 GT6 set up but where are other people placing their in-line filters?

 

Aidan

[dougbgt6]

I put my filter before the pump, there's a hose section comes up from under the sub frame. (Well, there is on mine!) Alternatively, on mine, there were three metal section with flexible hose between the pump and carbs. I've replaced these with one long flexible hose, you could do that and put it there?

[Guest]

Hello Leo.

 

You can purchase one of these via Ebay 130974315888 and does the job just fine.

 

On your set-up I would place it between the pump and the fuel filter; where you have stated that there is a section of rubber hose. Ensure that the arrow points in the direction of fuel flow to the carbs. This particular item I have flagged has such an arrow so no errors. 

 

You can go the electric route but it's a lot of money for what at the end of the day is probably a very simple problem.

 

It's not just the electric pump, you will need a pressure regulator to ensure your carbs are not over-fuelling etc.

 

---------------

 

Hello Aidan.

 

My Vitesse has solid metal pipe up until it gets to the thermostat area and then goes rubber; which lends itself nicely to an in-line filter and then of course the usual plumbing to feed the twin Strom's. I have not needed to install an in-line valve and to be honest there's not a lot of options open to you. Ideally, as mentioned to Leo it is best placed just after the fuel pump so fuel remains in-situ between the carbs and the valve itself. That ensures there is enough fuel to get the car running and by then the pump will have primed and be pushing fuel.

 

You could cut a section of solid pipe out just after the fuel pump and place the valve there. I think that would be your best option, but that is of course if you are happy to do that. 

 

Best wishes & good luck to you both.

 

Richard.

[AidanT]

Ahha, I never thought of it being before the pump. Actually shows one in the Parts catalog along with the fuel tank!  I will see if there's one there already! 

[AidanT]

Thx Richard - Probably best I get hold of the filter to start

 

Aidan