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Re: SU carbs

To: Bill Harkins <bharkins@tfb.com>
Subject: Re: SU carbs
From: edward <engconn@pottsville.infi.net>
Date: Thu, 14 Nov 1996 10:22:28 -0500
Bill Harkins wrote:
> 
> A great summary of SU adjustment. The  problem I am having on my TC is that
> I can run the jet nuts up tight against the stop and the car will still run
> and idle rich. Would "weak" needles help?
> 
> Bill Harkins

Bill:

It may not be a question of different needles.  How are you determining
how rich the mixture is?  By looking at the plugs? The exhaust fumes?
At what rpm is the engine 'rich'?  Only at idle?  If you are screwing
the nuts up all the way, and it is still rich at idle, then you probably
have a problem with the level of the fuel in the float chamber.  Check
the integrity of the float by removing it and shaking it.  If you hear
fuel sloshing around in it then it has a leak.  If that is the case, let
me know and I'll tell you how to deal with it.  If not, then you
probably have a leakage past the inlet valve, and I would suggest you
replace these with the GROSS types sold by Moss.  To test your attempts
at resolving the problem, drive the car at highway speeds, suddenly turn
off the ignition, and coast into a lay by.  Remove a plug and inspect
the points.  If the points show signs of a rich mixture after you have
rectified the preceeding problems(assuming they existed)then try
different needles or even smaller jets.  Perhaps the problem may be
incorrect centering of the needles causing the piston to stick a bit
without closing fully, or even worn jets and needles. The causes are
numerous.  Despite the idiotic comments made by some clown on today's
mail list when S.U. carburettors are correctly set up they are extremely
efficient at what they have to do, and most reliable.  The majority of
problems stem from tinkering with a worn out carb. which should have
been COMPLETELY and CORRECTLY rebuilt the first time.  Then the setting
up and continuing reliability is a piece of cake.  Bear in mind that no
amount of fiddling with a partially worn carb will result in first class
performance.  It is rather like hoping that  adding a supercharger to a
wanked out engine will revitalise it.  It won't.  It will just push
problems in another direction.
I am sorry, but I still do not have any factual quantative info to
impart re the fitting of Derrington heads.  I can only re-iterate that
they will enhace performance, but at the cost of traffic driving
flexibility.  I think the way you are going, namely adding a blower is
going to be a much better idea.  My experience with my Shorrock
supercharger on my TD is altogether most satisfying. The car is
tractible and flexible in it's traffic habits, and the performance most
gratifying.

Geoff Love, The English Connection.

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