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SU carb on Austin Allegro VP 1500

Hi I've got, as mentioned in the title, an old austin allegro (vanden plas 1500) from 1978/9. As you might have guessed by now, it doesnt like working. Im sure anyone who has owned one of these will probably agree with me. Anyway, the problem is this... The old SU carb, on it there is an overflow hole underneath the fuel line into the float chamber. whenever i start/try to start the car, fuel comes out of it. this is obviously a problem, its meant to be going the other way. this only happens when the engine begins to catch. i have blown through the "route" to the main part of the carb and all seems fine, but the petrol is obviously being refused entry somewhere. the float assembly is fine and moves freely. this has me in a bit of a muddle. there doesnt seem to be anything wrong with it, except the petrol doesnt want to go into the carb. Has anyone got any ideas? I'd be very grateful, I'm meant to be learning in this beast lol. Its brown too :-) Thanks, Simon

Reply to
Simon Dixon
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I am just guessing because I don't remember a gas 'overflow hole' on my

3 old Austin Minis SU's, it has been a long time but they have an electric fuel pump and have a sealed system.

Are you maybe talking the air vent for the float bowl?

I would suspect so and if so, that means the float shutoff valve is toast, the needle and seat. Pretty common on older carbs of any type, high wear part.

The float also could have leaked and sunk making the fuel level in the bowl too high at idle or start.

Basically, I am thinking too much gas is getting into the carb at start and pouring out the vent hole.

A kit could do it wonders and kits are cheap. They come with the gaskets and a new fuel needle and seat as they are a high wear part.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Sim>

Reply to
Mike Romain

thanks very much. two problems- 1. the carburettor seems to be pushing the petrol BACK through into the float chamber, why would this happen? and 2, i placed a washer on the housing to the jet that site abouve the float, to lower it, and shut off the fuel earlier (as an attempt at a remedy, this didnt create the problem) the petrol still leaked out and in my mind, this should remove the problem of worn float/jet?ive tested the float and it, erm, floats well. I dont have much experience with SU's, so is it possible that thers is something going T*** up further along the line?

Reply to
Simon Dixon

I agree with Mike's diagnosis. Check the end of the float needle with your thumbnail. It should be a smooth cone. If there's a step or notch in it, you'll never get the float level right, you need a new needle.

No. The float level is set by bending the brass arm that rests on the float. With the piston and bell removed, look down into the jet. You should see gas just level with the jet orifice. If it's lower you bend the float lever upward with a pair of pliers, or if it's gushing out you bend the other way. Bend in the flat area just beyond where the lever contacts the float needle.

I do. An MG and four Jaguars saw to that. I can give e-mail lessons.

Reply to
John Ings

I dont seem to have a brass arm. i have a pointy thing, i assume the jet, which moves up and down and blocks off the fuel (in theory)but no adjusting arm. would this be the problem then? it hasent had one since we got it and before that, i doubt if anyone looked into the carb, it's done 25000miles since 1978

Reply to
Simon Dixon

I think he is referring to the portion of the float that the needle vlave is resting on. The float assembly is usually made of of two parts a brass arm acting as the hinge attached to a plastic float. As the fuel level in the bowl goes up the float will rise and push up against needle to shut off fuel flow. To adjust the bowl fuel level that brass arm is bend to change the level at which it push up against the needle valve to shut off fuel flow. On some SU's there are no brass arms hinge on the float to adjust, the entire float assembly is plastic, in that case you will have to find some thin washers to shim the needle valve to set your float bowl level.

Reply to
Dave Chu

Is the float made of brass or plastic? The plastic kind doesn't use an arm.

With gas overflowing from the float bowl?

Anyhow, here's a source of parts--

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And some tuning tips-
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Reply to
John Ings

No, you're not even close to looking at the float. You're looking at the piston and needle. Depending on whether you have an HIF or an HF SU, the float is either in the chamber off to the side of the main carb body, or in the chamber at the lower end of the main carb body.

You REALLY don't want to mess with any carburetor, particularly an SU, without knowing what you're doing or at least having a proper reference text.

The Burlen people are now the manufacturers of all SU carbs, parts, and manuals:

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DS

Reply to
Daniel J. Stern

Thanks all, I do have the plastic float (with no arm) so it must be that they are simply worn out then. sorry for my ignorance, i'm a teenager :-) I was also talking about the float chamber, to the side, not what i believe is called the bell chamber? i dont know. anyway i shall read up on these links, and get myself one of those float kits. Thanks very much, Simon

Reply to
Simon Dixon

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