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@rcn.com
'80 Spitfire, '70 GT6+
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