Thread: Running a 235 chevy at lower RPMs

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I put a stock sized jet back in the carb and will need to take it on a small trip and see how it does,the plugs looked like it was running a little rich and putting the taller gears has changed the fuel demand of the motor alot since when it had the 4.10s the plus were always burning white.

With a Rochester Vacu-jet carb that is stock equipment on a '57 235, it will have very little manifold vacuum at cruise with tall gears. I don't recall the spec's, but I'll bet the power enrichment valve is open on your carb at cruise speed, that causes high fuel consumption. You can experiment with different springs above the piston or snip a bit off a spare spring and see if that makes any difference. Remember, less spring tension delays the valve action, no spring at all defeats it entirely.
Put a vacuum guage on it and drive by it, keeping as high a reading as you can. I'll look in my books for the vacuum values for the carb valve, but I don't recall seeing them for years. Too many books!

As for your speedometer being wrong, S10 FWD's have nifty little gearboxes that go on the trans end of the cable and change the cable RPM. Any I have gear it up for lower ratios, though, may not be made to go the other way.