[Healeys] SU Carb tuning

[Herbert Miller]

"In any case as Alan points out this only has to do with idle settings and
I think we are more concerned with mixture at mid to high rpm ranges
depending on how we use our cars."

   I do not think this is true. 
Assume that at a particular butterfly opening the piston will rise to a
particular position independent of mixture setting, a valid assumption I
think. If the jet is positioned further below the bridge ie a richer
mixture, as the piston and needle rise the mixture is richer through the
needle travel.
   Think of it this way. The enrichment for cold starting for most SU's is
to lower the fuel jet. This enriches the mixture for cold starting. If this
only enriched the mixture at idle, the car would be undriveable when cold.

Herb Miller 
 

-----Original Message-----
From: healeys-bounces at autox.team.net [mailto:healeys-bounces at autox.team.net]
On Behalf Of Awgertoo at aol.com
Sent: Saturday, March 28, 2009 5:32 PM
To: healeys at autox.team.net
Subject: [Healeys] SU Carb tuning

I too had always been under the impression that lifting the pin  on a 
particular carb gave an indication on its--versus its partner's--state of  
richness/leanness until quite recently a very smart and experienced mechanic
friend 
said it was just the opposite and explained why as this string bears  out.
Volvo 
and Healey SU's are both the same in fucntion--and one  would think that the

Brits could explain in better and more accurate  English the operation and 
tuning of an English carb than could the  Swedes, but who knows!  
 
In any case as Alan points out this only has to do with idle settings and  I

think we are more concerned with mixture at mid to high rpm ranges
depending 
on how we use our cars.  I still prefer to run the car at a  particular
speed, 
then shut it down and read the plugs--NGK in my case--as they  do not lie.  
 
Best--Michael Oritt
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