13 replies to this topic

[jinjrich]

Hi all
Theres supposed to be a piston lifting pin on my carb somewhere, but i cant for the life of me find it. Its an SU carb on a 1989 designer. Can anyone help? Thanks

[2lrminivan]

as you look at the carb it will be on the left i think toward the back edge under the piston/dash pot
are you sure it should have one.
why do you need to find it?

Edited by 2lrminivan, 23 January 2010 - 03:38 PM.

[jinjrich]

We've fitted a stage one kit, and just till we can get it on a rolling road i need to get it running ok-ish. Following haynes the procedure involves lifting the piston... Or is this just typical Haynes (un)accuracy?

[2lrminivan]

as far as i no u only need to lift it to make sure the piston is not stuck but i might be wrong.
what is the procedure then ?

[bmcecosse]

Haynes for once is CORRECT! But - not all SUs have the handy little pin. In which case - use a small thin blade screwdriver in the front of the carb - and lift the piston with that. Just an 1/8" inch is all!! Otherwise - just twiddle the mixture back and forth until you get the smoothest/fastest idle. Generally RR is waste of time/money - since most operators have little idea of the Mini or the SU carb. If you have the AAA needle in there - and set the mix as above - then road test it - switch off after a goodish run under power - and pull a plug out. Should be light tan colour - if white it's too weak - if black it's too rich. You should also advance the ignition until you get a little pinking under load - then take it back slightly so it's just 'not quite' pinking. That's the best you can do - unless you know how to change the advance curve in the dizzy.

[jinjrich]

Ahhh ok that would make sense, thanks. I think once the idle is set your'e supposed to lift the piston and listen to see if the revs drop, rise or stay the same. But i'm not sure as i dont have the manual with me right now. Think i might get it sounding/ticking over right and then look at the mixture.

[jinjrich]

Haynes for once is CORRECT! But - not all SUs have the handy little pin. In which case - use a small thin blade screwdriver in the front of the carb - and lift the piston with that. Just an 1/8" inch is all!! Otherwise - just twiddle the mixture back and forth until you get the smoothest/fastest idle. Generally RR is waste of time/money - since most operators have little idea of the Mini or the SU carb. If you have the AAA needle in there - and set the mix as above - then road test it - switch off after a goodish run under power - and pull a plug out. Should be light tan colour - if white it's too weak - if black it's too rich. You should also advance the ignition until you get a little pinking under load - then take it back slightly so it's just 'not quite' pinking. That's the best you can do - unless you know how to change the advance curve in the dizzy.

Thats just what i needed, many thanks! I'm still not sure where to lift the piston though, can you help further?

[bmcecosse]

Just lift it with tip of the screwdriver! It has to be small - to avoid upsetting the air flow and spoiling the result.

[jinjrich]

Just lift it with tip of the screwdriver! It has to be small - to avoid upsetting the air flow and spoiling the result.

Great! Will give it a bash tonight

[bmcecosse]

NO! Don't 'bash' it - just a gentle lift!

[jinjrich]

NO! Don't 'bash' it - just a gentle lift!

Hahaha got it!

[Ethel]

Even if the operator has never seen an SU they would still be able to monitor the AFR under load and see if you're running lean enough to melt your engine. I do agree there less point on splashing out on a RR session for a car that is almost standard and it would be nice if the operator was well versed in the black art of needle profiling.

Lifting the pin should cause the revs to rise briefly before settling back down. If they rise and stay up it is too rich. If it stutters on the point of stalling it's too lean.

[bmcecosse]

If it's an AAA - it won't be too weak - and the plug check will confirm.

[stormintrooper]

my local guy that does RR's can do needle profiling too