Help ! Mystery of leaking carb.

[spitfire moneypenny]

Hi, I would appreciate some help.
I recently acquired a Spitfire 1500, 1976 P reg, and have noticed a strong smell of petrol when accelerating quite hard, and also stuttering of the engine.

I have traced the source of the petrol smell to fuel leaking from one of the carbs. Type SU HS4,  ref AUD665F (front carb). It seems to be coming from the base of the metal inlet tube which forms part of the float chamber lid, although it may be where the fuel line is clipped to the metal tube, it is difficult to judge. The thing is, on tickover it seems fine, but once warmed up and suddenly revving the engine to about 3K there is a sudden burst of fuel coming out of either a)  where the flexible pipe meets the metal tube, or b) possibly the housing around the tube on the float chamber lid. I think it may be the latter as I have replaced the flexible line with 6mm flexible fuel hose, and even used 2! clips to fasten it to the float chamber inlet, and still it leaks under sudden pressure, but not fast idling, or slow acceleration, only when sudden acceleration, and not always even then!, it seems intermittent.

It is not coming from the gasket joining the lid to the float chamber. I have taken the lid off and the float seems fine, and the jet does drop down, but I have not taken it apart.

Is it possible it could leak from the metal casing housing the pipe on the chamber lid, maybe as designed overflow if the needle sticks?

Can anyone suggest a remedy that is not too expensive?

Sorry it’s a long explanation, I’m a retired civil servant and hence long windedness is a hazard acquired from the job!

Thanks to all,      Clive

[Clive]

needle valve. Probably worth replacing, under £10 and very easy to do (but would humbly suggest a few  taps with a light hammer on the screws that attach the lid to the floatchamber before attemping to unscrew. They can and do seize and shear)

Another Clive!

[Deleted User]

There is an overflow hole in the float chamber lid.  
Early lids had the hole hidden behind a small steel cover that is just below the inlet pipe.
Later lids made it a bit more obvious, with a separate pipe connection - but they didn't connect a pipe to it.
The very last cars had a pipe connected to the overflow outlet to direct any overflow down to the road - away from a hot exhaust !

I would suspect fuel pressure, possibly a faulty fuel pump, or some crud trapped in the needle valve.

[CharlieB]

And fit a fuel filter if you haven't already to stop any more crud getting to the needle valve

[spitfire moneypenny]

Thanks to you all, I think youv'e nailed it. I wondered whether it was a sticking valve and if there was a hidden overflow and youv'e confirmed it. Looks like Rimmer Bros for a new needle valve and back on the road asap. Don't want to miss this great weather.
Thank you all very much.