We have been working on a 1968 Spitfire Mk 3, It is a stock, very origiinal
car. We have just done a valve job, installed hard exhaust seat and new
guides, & replaced the rings. The compression is great and the engine is nice
and tight. It has the stock tubular headers that cam on this year car and the
dual 1 1/4" HS-2 carbs.
We are having a tuning problem. With 2 psi fuel pressre at the carb at WOT
the engine runs lean, especially at part throttle. The stock spec. calls for
"DD" mixture needles. They are way lean. Just bringing the revs up from idle
to about 2500 to 3000 rpm with no load the engine spits and runs very rough.
Adding fuel makes the engine "rev" right up. We have tried progressively
richer needles going from the "DD" to "AN", then to "H-6" and finally to "DK"
needles. With the "DK" needles installed the engine runs"GREAT' under any
circumstances
but I am afraid that it is to rich. I took it on a 35 miles or so road test on
Sunday with these needles installed and it was a pleasure to drive! but seemed
to just "suck" gas, but this is a subjective judgement as I was not able to
measure the fuel economy. Note, the cam, displacement, etc. are all stock in
this car. I am at a loss to understand why the needles need to be so much
richer than the stock spec to make this car run properly!
Does anyone have any ideas or experience with this exact model?
Greg Solow
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