Fuel leak from the carb!!!

[jlo1986]

HI guys,

I have a bit of a problem as there seems to be quite a lot of fuel leaking from the front carb on my late 1500 spitfire. It drips when it's idling or at revs and continues to drip after the engine is turned off. Unfortunately I need to get this fixed urgently as the mot is up soon and I need to replace the down pipe gasket on the exhaust, but the bolts are seized so want to put some heat on them but can't do it when there petrol everywhere!

I've had a look tonight and it seems to be coming from the end of the flexible pipe at the bottom that connects the main body to the float chamber. I think it might be where the hose meets the main jet and if so do you think changing the main jet would stop it? I think the part no I was looking at was AUD2427 on rimmers website.

Thanks in advance guys- I always seem to be asking questions and never answering them so thanks for all the help so far!!!

Jamie

[Spitfire1500]

Hi Jamie,

Is the float unit itself all right? Check the three screws are done up tightly and that the leak isn't coming from there. Also make sure the leak isn't coming from one of the fuel pipes themselves.

The fuel pump is located on the rear left (behind the engine block) and in front of the bulkhead, see if the rubber pipes here aren't also leaking as this could also be leaking. You'll know it because you'll see three cables off it - two fat rubber ones, one goes to the fuel tank the other to the rear carburettor and a third cable which also goes to the rear carburettor - but a much thinner one.

I'm not sure you can get a new main jet very quickly - normally, 2-5 days it takes for delivery but perhaps you know a company locally, so you can pick one up locally? AUD sounds like one of the earlier solid jets, putting new jets in is quite simple - but may be made easier if you take both carburettors off.

I won't go into details as I've done it only once before, but it's a case of unscrewing the choke linkage, doing the same for the throttle linkage, unbolting the carburettors from the inlet manifold (There are 4 bolts) laying down both carburettors, checking butterfly valves as well as gaskets, then you should see the carburettors pretty much separate. Then you have to undo the throttle and choke linkage bolts on the front carburettor, unbolting the float unit to jet cable (the bolt is on the float unit) and then the jet should just pop out and you can put your new one in, bolting it back onto the float unit and then reversing what you just did.

I hope this is helpful! Good luck,

David

[jlo1986]

I have checked and I don't think any of the fuel lines are leaking and it doesn't seem to be the float chamber as the side and top are dry even when the fuel is dripping from the union at the bottom of the float chamber and the flexible tube.

I have checked this union and it seems to be tight so as I said I think its the bottom of the jet, My mot is up on the 10th so I’ll just have to order a new one and wait. A couple more question though- should I replace both the jets on both the carbs to balance them or can i just replace one?

Thanks for the help so far!

Jamie

[Paul318UK]

Check the float itself isn't leaking and sinking! This or a warn shut off valve will allow fuel to flood the carb. Take out the plugs and check the ones on the problem carb arn't darker, this will indicate excess fuel,

Paul

[CharlieB]

It could be the seal where the jet hose screws into the bottom of the float chamber, they sometimes don't seat properly if you don't screw them in carefully.

[Deleted User]

I've had a float become a "sink" when it got a hole in it and filled up with fuel. This caused a fuel leak like you've described. It might be worth checking the float out before you order any parts you don't need.

To find out where the fuel is coming from, use a mouse's ear. It's a tissue rolled up at the corner to form a fine point. Dry the carb off, then run the tip of the tissue along any suspect joints. Immediately it contacts the source of the leak the tissue will wick up liquid rapidly by capillary action and become damp. You should be able to pinpoint the source of the leak accurately using this method, it works really well.

[Lord Sorbington]

My 2000 has a tiny leak from the jet adjuster screw under one Stromberg carb.  I renewed the jet assembly to float chamber seal but the leak continues.

There is an O ring in the jet adjuster and it seems its this which is leaking. Will have to remove the carb again, dismantle the jet adjuster to change this.

[jlo1986]

Right-

I've had the float chamber off again and opened it and the float seems fine and I have traced the leak and it is definitely coming from the bottom of the jet (see my very well annotated pic!).  It looks like I am going to have to bite the bullet and buy a new jet, unless anyone else has had any epiphanies as to what it could be?

Cheers, Jamie