I've gotten measurably different dyno runs from morning to afternoon with no modifications, until we figured out there had been a big change in the relative humidity. It was hard to believe that something as simple as a thunderstorm passing by during our lunch break could skew the numbers that much! While your O2 sensor is better than nothing for evaluating modifications, don't forget to factor in things like ambient temperature, atmospheric pressure, and humidity when analyzing your data. Have fun!
It night be a good idea to find a slightly stiffer spring for the power piston, so the power valve opens up a bit sooner. The guy with the dual carb setup is probably going to make a massive change toward the rich side somewhere, to compensate for the loss of venturi velocity by splitting the airflow between the two carbs.
Jerry
