Bob,
I would not change the Venturi size, mostly because of cost vs benefit, but
also because the smaller size gives you a higher vacuum (signal) to control
the fuel. I personally don't think you will be able to tell the difference
in power under normal driving and think it will make a much better daily
driver with the smaller venturi. You most likely will have to reduce the
jet sizes - I would bet that 40s are set-up for a smaller engine. I know
that sounds wrong, but with the higher the signal, the more fuel the jets
flow. Put another way, if you increase the speed of the air flow through
the carbs, you reduce the jet size. I suggest you check out some of the DIY
EFI web sites.
Many discuss how to make a gauge or use a volt-meter to determine your
mixture using the signal produced by an O2 sensor. I would estimate it
would cost 100 or 200 for the O2 sensor, having a fitting welded your
exhaust and parts/purchase of a gauge. IMHO this would be money well spent.
Phil
Philip Erickson
San Diego Calif. 92121
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