su carb austin allegro 1500 I NEED HELP!

Hi As some of you may remember, i wrote on here about a month ago relating to the SU carb on my austin allegro, and its flooding problem. I took your advice and replaced the float assembly, which solved that problem. however now i have a seperate, though related, problem. in my first attempts at diagnosing the problem, i was a fool and took the carb apart, without noting idle screw positions, etc. as a result, the old girl is now running like a pig. i have tried to set the carb up, however it seems impossible, as the engine keeps racing for about two seconds, and then dropping revs dramatically and doing it all again. this would be the problem. how do i make the engine maintain a constant idle? it seems pretty vital to me that this needs to be done before i can get it running at all well.

Also, and probaby not related, but there is a constant whine/squeal which raises pitch and volume as the revs increase. i have a feeling this could be the bearing in the water pump, as the carb caught fire a few weeks ago and it could have meted/spoiled/whatever the grease in said bearing, as it is quite close.

thanks in advance, Simon (email doesnt work, try snipped-for-privacy@hotmail.com if need be)

P.s. Sorry for re-posting this, i've gotta learn in this thing and it isnt much use if isnt working. thanks again, si

Reply to
Simon Dixon
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Approximately 10/14/03 10:34, Simon Dixon uttered for posterity:

What idle screw?

On the SU's and japanese clones I recall, the idle was set by adjusting the jet on the bottom of the carb up and down.

First you run the jets up flat with the base of the carb, using a razor blade to verify. If you only have one carb, this isn't necessary, just raise the jet up more or less flat across the bottom of the carb.

Then you turn the adjust nut to lower the jet. Start with about 1.5 turns, then start the engine and hope it runs.

With the engine running, you lower the jet and test the mix by pushing the SU piston up with the small button found under the carb. You can also use your finger to lift the piston about a quarter of an inch. If it is adjusted properly, the engine rpm will speed up a bit for a moment, then drop. After EACH such test, be sure to clear the carb and idle by using the throttle cable to bump the rpm at least a thousand.

There are books for rebuilding and adjusting SU carbs. With care, the SU can produce pretty close to the power of a Weber, for about 1 millisecond, then it goes out of adjustment again.

But what do you expect for a carb that is really a toilet valve modified?

When working on the carb, keep a CO2 fire extinquisher handy.

Reply to
Lon Stowell

Simon got the instructions dead on, but first check that the needle is correctly installed into the piston. Also, put some thin oil into the piston damper - I use 10w30, but there may be a sped somewhere. I imagine ATF would work too. When you took the carb apart, did you take the butterfly out? It needs to be closing properly for all this to work in the first place, of course...Also, did you put the big floppy spring back in?

Cheers, Brian

Reply to
Brian

You could be describing a vacuum leak. Do you have an emissions canister on that thing? That would be the vent for the gas tank and carb float bowls. A dead purge valve on one of those will cause your symptoms.

A dead PCV valve can also cause surges like that.

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

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