Jaguar XK140 fuel leaking from carb

[Mikebentley]

Hope someone can help I have a 1955 XK140 with I believe HDU 8 Sandcast manifold and I believe HD type carbs. Just started it up and pulled out of garage and turned engine off. Several hours later went to reverse back in and it was running very lumpy so I popped the bonnet and fuel appears to be flowing from a metal pipe coming out of the top of a unit to the right of the main carb body. Is this an Auxillary carb?

Any help with what the cause might be and how to fix?

Sorry but not super skilled but keen to fix if I can as can’t safely drive it with copious amounts of fuel everywhere.

Thanks in anticipation
Mike

[Mikebentley]

Thinking it might be a starter carburettor as it is attached to the front carb if this help anyone.?

[littleredrooster]

I'm guessing that it could be a float chamber, and either the float is stuck/faulty/full of debris, or one or more fibre washers need to be renewed, depending on where the leak is.

Difficult to say without a closer look. You could give it a tap with a screwdriver handle (or similar) to see if it releases the float (but it needs to be a properly calibrated tap...don't break it!)

[Mikebentley]

Thanks Littleredrooster I just looked in some books I have and I think you are right. It appears to be something called a “starter carb” which functions very much the same as the main carbs and has this tube which comes out the top and then about 3 inches down almost like an overflow. The car fires up and will run but there is a steady flow of petrol out this tube.

I think I will systematically dismantle it in the morning and clean and replace anything obviously knackered to my amateur eye. It’s as if it primes and then stays open resulting in an overflow when the main carbs are running. I have been experiencing issues recently where it once started seems to idle at about 2000rpm which made driving a pain and I couldn’t seem to see why but again sticky or blocked floats somewhere could be all linked.

This Jag fights me every turn whereas my Vitesse has a bit more access but virtually never goes wrong.

[GreenV8S]

A stuck float seems unlikely to cause a high idle - for that you're looking for an air leak, or something preventing the throttle from closing fully.

[Mikebentley]

GreenV8S I take your point on the idle and have tried lots of things to bring it down even checking carpet around accelerator pedal but priority is sorting the fuel leak. When this is fixed I might get the carbs stripped and rebuilt.

[stevieturbo]

If it is idling at 2000rpm....there IS too much air getting in.

[Peter3442]

The picture shows the float chamber. The starting carb sits next to one of them. If it's staying on, it's usually the thermo-switch in the manifold that isn't opening when the engine warms. You can switch it off by pulling the lead off the switch (or more permanently by wiring up an extra switch inside the car). However, when the starting carb stays on, the mixture is way too rich for the engine to run at all, unless there's a lot of air entering from somewhere else.

[Mikebentley]

[Mikebentley]

Peter thanks for reply slow Sunday start so just seen it. I have uploaded a couple of extra pics. Am I correct then that the thermoswitch is the black one with the button on top between the carbs with the white and black wire? If I temporarily detach this the overflow of fuel out of the starter carb should stop? I can then address the mixture issue (excess air) that is causing the over fuelling then reattach thermoswitch?

Sorry for all the questions but I am learning as I go. Really want to learn these things as knowledge is dying off and source of people to ask is also. My old dad would have known but dementia got to him before I could ask.

[Mikebentley]

There is also an auto choke switch inside the car that I pull on and a bulb lights up next to it when on. It then requires manually turning off when the car will idle. I presume one of the wires runs to this then.

[Mikebentley]

Just disconnected wires off thermoswitch and started car. Fuel still flowing from overflow pipe ( that’s what I’m calling it) on starter carb in front of front main carb and also just noticed fuel coming out of button between two flat head screws to right of thermoswitch body

[Mikebentley]

[Mikebentley]

[melhookv12]

The float is sticking/badly adjusted as previously mentioned. Remove the screws and check inside, you should find instructions in te manual for the correct height setting.

When set correctly the float will stop the fuel over filling.
Might as well check the rear one aswell.

[Mikebentley]

Update, took the lids off the tops of the two auxiliary carbs to inspect the floats. The front (starter carb) float was decidedly sunken with approx 8mm of fuel sat above it, the rear bobbed up and down freely when tapped and the upper part of the float was crowning above the fuel line.
I then using a squashed toilet roll tube pushed between side of float and chamber wall removed the offending float. It contained fuel so could be more accurately be described as a”sink”.

A guy I know directed me to a very well known and local to me SU specialist (2 miles away) who after 5 minutes told me to come round. After half an hour of great chat he furnished me with a replacement used float which he cleaned up. Wouldn’t take any money (gave him a tenner) and returned home and refitted it after cleaning everything with carb cleaner......hey presto one very fixed Jaguar.

I will take car to him next week and get him to set up mixtures etc. and now have a new contact and hopefully friend as he was a top bloke.

Thanks all for your input and another new semi skill learnt.