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Carbs Leaking Fuel

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Hi Everyone,

I am in the process of getting the Excel back on the road and as part of this I had the carbs rebuilt as I am not sure they have ever been done in the past.

They were sent them to Eurocarb and the guys did a great job with the carbs looking like new.  However once everything was connected up both carb's are leaking fuel through the venturi's.  You can also hear the pump still ticking although very slowly.

On checking the float heights they were perfect and matched the settings in the Des Hammill book.  

As both carbs are leaking a sensible starting point seems to be to check the fuel pressure (although never an issue before so shouldn't be now) to at least eliminate one possible cause.

My plan is to plumb into the pipe just after the fuel pump to check and then remove straight afterwards.

So my question is what size thread is the union that connects onto the fuel pump as pictured below?  If possible I want to connect some pipe to either end of the gauge and then get some connectors to the pipe that allow me to temporarily connect it to the car.

Also if anyone has any advice on what else could be causing the issue please let me know!




Edited by crs_20
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Sounds like the float needle valves aren't sealing fully, part number 13 here, I'd whip the top off the carbs & check them first. 😀


John W

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When I checked the float heights I looked at the needle and seemed to be seating ok.  The needles were replaced as part of the rebuild so should be ok in theory.  I want to check the fuel pressure so I can eliminate one potential cause, as at that point the issue has to be the carbs themselves.  

Good point on the fibre washers I hadn’t even noticed!  Will get them changed.

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The carbs only leak when the pump is on.  It is a slow leak so the float / needle is cutting off most of the flow but not quite stopping it.

I spoke to Eurocarb, they reckon that it is very unusual for there to be an issue and the fact that both were doing it even less likely, so suggested that the fuel pressure was probably too high.  

If I can find out the thread onto the pump then I can get a Barb hose connector to plumb in the pressure gauge.  Even if the pressure is ok, which I suspect it is, one possible cause will have been Eliminated.  

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I would check the pressure at the carb end of the pipe work as that deals with the slight height difference from the pump to the carb. I bought a somple low pressure gauge off eBay and made a  temporary connection at the carb input and went from there. 

I would add that the correct SU pump will deliver the correct pressure so I would check the needle valve in the float chamber. The standard needle is all brass but there is a version with a plastic type seal ring round it, I had flooding trouble and despite all new parts and the correct pressure, I still had leaks, changing the needle fixied it instantly.


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  • 1 month later...
  • Gold FFM

Curious.  I would choose Viton over brass any day.

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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