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MG MGA - Carburettor holes

Sorry for my ignorance, but I was interested to know the purpose of the hole on top of the float bowl. Is it to allow air to escape as the fuel comes in?

You will see from the photo that my carburettor lid has a brown stain on it. I assume that is from escaping fuel that gets fried on the lid? Is that normal?
But the car is running very well.

Many thanks.


Graham V

Graham, It is indeed a breather hole but later SU's (such as in your photo) have breather tubes carrying excess fuel (if the carbs flood) out harm's way. I put new needles and seats in my SU's when I am restoring or "doing up" my cars. They are very reasonably priced.
Barry Bahnisch

Graham

I have one observation about your overflow pipe. If you have a full length pipe and routed the way it was originally, then no problem. However, if it is a shortened pipe (which many of them are) then, in that position it drains straight down onto the exhaust pipe.

My pipe is straight down and I have put it 180 degrees out to yours so that it drains well clear of the exhaust.

Steve
Steve Gyles

Graham-
That boss is an artifact of earlier carbs which had "tickler pins" fitted there. There should not be any actual hole on carbs without pins.

The banjo fitting with tube on top - and the correct washers - are the venting and incidentally the overflow should that be needed.

Steve-
Thinking that you are accomplishing anything by re-aiming a short vent pipe is delusion of the first order. Even when the pipe is directing fuel right on to the hot manifold the fuel turns to vapour before it makes contact. With all the strange airflow that exists normally in the engine room, - not to mention the mad aero guys - the fuel will be someplace else before you can figure out where it was going, and it is vapour that is the problem anyhow.
Make the pipes the correct length.

FRM
FR Millmore

Theory is good FRM. Not going to argue. Caught fire on an autobahn with a flooded carb in 1971. Symptoms were a misfiring engine. Stopped on the hard shoulder. Switched off. Opened the bonnet (hood). Whooof, up she went. Kiddy in the back; 2 door Ford Cortina. Quite frightening.

Steve
Steve Gyles

Many thanks for the responses. So the hole goes nowhere - that makes sense. But any idea then what causes that brown staining on the top? Is that normal or a sign of something wrong?

Steve. I thought exactly the same as you and shortly after taking the photo, I spun the pipe round. I am sure FRM is right in what he says, but it doesn't do any harm.

Graham
Graham M V

Graham-
Staining is from fuel seeping out the gaskets on the pipe, or creeping up from the edge of the bowl/lid gasket.
It is easy enough to replace the pipes - they are just regular 3/16 steel brake pipe tubing, or you can use copper, or just rubber hose from the stubs down. When I started I was told to cut them short, and I cut a lot of them; then I thought about it and have been replacing them ever since as payment for my sins.

Steve - Enough to make you start going to a church where they worship fire extinguishers! I am a bit worried as I drive my newest beast, which has a leaking tank on one side and a twice busted exhaust system on the other; waiting for parts.

FRM
FR Millmore

FRM


In those days I did not carry a fire extinguisher, but have done so ever since. A passing German motorist pulled straight in and put out the fire with his extinguisher, then towed me to a garage. Really nice guy.

Ten years ago I was able to do the same when the car ahead of me went out of control (driver on drugs) and went head-on into oncoming traffic. I was first on the scene and smothered the smoking engine compartment while others did first aid on the trapped driver. The thought of fire in a car puts the fear of god into me. I trust all MGA drivers on this BBS carry a decent fire extinguisher.

In the MGA I have it attached to the cockpit wall so that I can reach it even when strapped in tight.

Sorry, marginally off topic.

Steve




Steve Gyles

Still off-topic! I carry fire extinguishers in all of my cars but not always the best access! In the MGA's I hide them in the luggage boot! Never had to use one but worth it for peace of mind!
Barry Bahnisch

This thread was discussed between 19/08/2012 and 20/08/2012

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