Ross, Bob, et al,
I'll throw this out for what it's worth (Bob, you should already have
this info). Spitfires with twin SUs will have two different fuel levels,
no matter how carefully you adjust the floats to spec. The Spit engine
has a 3-5 degree tilt down and aft. The front float bowl is forward of
the front venturi, and the rear bowl is aft of the rear venturi. With the
twin stock AUD 2140 bowl configuration, no matter how carefully you
adjust the individual float levels, the front fuel level will always be
higher than the rear. Therefore, set equally, the rear carb will
always run leaner than the front, and the front will be more prone to
flooding.
To find out how your carb float levels are actually running, remove the
pistons and, with the car on level ground, look down into the jets. I'll
bet you the front jet will have fuel right up to the top of the jet, and
the rear level will be somewhere down the jet, beyond view.
Couple that condition with high speed vibration, or lumpy idle, and fuel
is bound to spill out the vent and the jet of the front carb. If fuel is
also coming out the rear unit, then that float is still too high or
there's crap clogging the needle valve.
Cure? Either shim, or bend, the front float level down, or replace the
rear bowl with an AUC 1310, which has a 1/4" higher offset--again, some
shimming or bending will be required to balance the levels. Can you say
"Carb tuning"?
I think you'll find that, with balanced fuel levels in the jets, the
carbs will be easier to balance, and front carb flooding will end.
But then, this is only a suggestion.
Charlie B.
Spitfire Pilot
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