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MG MGA - SU Carbies

Hi Guys,

A curly one for you technical people.
I've just returned from a dyno test on my MGA powered by twin 1 3/4 inch SU Carbies. Was very rich at lower revs up to 3000 rpm and lean over 4000 rpm using a W02 needle. Has anyone experimentes with a needle that is leaner in the lower rev ranges?

Dave
David Godwin

You might try contacting Joe Curto, the S.U. Carb expert in the US. He has a website. He could probably get you the correct needle.

Just out of curiosity, do you notice any performance benefits over stock 1 1/2 inch carbs?

M.D.
'57 Coupe
M. D.

David,

My brother and I dabbled with 1 3/4 SU, before switching to Webbers.

I might associate running lean at high RPM's with a weak fuel pump or incorrect float.

I have a collection of springs for inside the dashpot and applied them as needed.
A lighter one will = leaner & vice versa.

You can also slide the needle up and down in the dashpot. Up for richer ... vice versa.

Cheers
Mark.
Mark Hester

MD
I bought the car with 1 3/4 carbies, which were extremely worn out. I did a dyno before replacing them with reconditioned ones. The first dyno showed 84hp and a serious peak around 6000rpm. The new carbies, with different needles (they are not interchangable - one is a fixed and the other a floating needle)produced 80hp but a much nicer curve - more down bottom, BUT at 5000rpm!
Both needles are rich - off the screen- up to 3000rpm.
Hence my initial question.
I received 2 sets of needles to try this afternoon from our local supplier - Midel - in Sydney, so will report back next week - also with the correct needles in question.
Dave
David Godwin

This thread was discussed between 26/07/2006 and 27/07/2006

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