[TR] Good tri-carb manifold?

[Jim Muller]

On 26 Apr 2009 at 8:08, Anthony Rhodes wrote:

> You need to use a different spring, and the exact spring
> strength will be strongly influenced by the exact specifications
> of the engine.

I can't speak to the specifics of the TR6 engine but I can say from 
experience that Anthony speaks truth.  When I got my GT6 it had a 
pair of SUs taken from an MGB.  The mixture behavior was best 
decribed as "peculiar".  If adjusted for decent idle it would stumble 
and misfire at part throttle when warm, but would dart like a 
champion when the loud pedal was pushed.  Idle aside, the 
relationship between part- and full-throttle made no sense until one 
considers the springs.  At part-throttle it was running lean.  At 
full-throttle the pistons would bottom out (i.e. top out) early so 
that the venturis would not enlarge any further.  This makes the 
mixture richer.  At some point between part- and full-throttle it 
must have made the transition from too lean to too rich.  The needle 
profile could have corrected any idle-to-part-throttle mixture 
differences, but no amount of needle swithcing would have changed the 
difference between part- and full-throttle.  Joe Curto made the 
diagnosis and sent me springs appropriate for the higher flow rate.  
Problem solved.

-- 
Jim Muller
jimmuller at rcn.com
'80 Spitfire, '70 GT6+