Charon
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The topic of improving airflow by making changes to the intake system has arisen before. However, I have seen no documentation on this forum of any measurable effects. One or two people have posted dyno charts, some of which have vanished. As far as I know, no one actually posted a dyno run of, say, a stock bike followed by a dyno run on the exact same bike with the air filter removed. Or for that matter, with the entire airbox removed. At least one of the posted dyno runs did not have the exhaust gas analyzer connected, so it was impossible to see whether the mixture changed with engine RPM, an effect I would expect if there is airflow restriction. Some of the posted runs have had incorrect RPM measurements, which have led to incorrect torque and/or horsepower measurements. In short, all we seem to have are "seat of the pants" measurements, and we all are susceptible to the placebo effect. If it's noisier, it must be more powerful.
By the way, unless the high-altitude airbox openings are reversible, the leaned high-altitude mixture will remain to plague the engine on the return to low altitude. Airplane carburetors have a pilot-operated mixture control, which changes gasoline flow to compensate for air density (altitude) changes. If I remember correctly, my old Trail 90 had a carburetor with an altitude control on it - a two position control for above or below 6000 feet. It made no difference that I could tell, but I never had the chance to take it over 6000 feet.
As a matter of interest, it seems to me it would be possible to convert a CV carburetor to non-CV operation. Block the air passage from the venturi to the top of the diaphragm, open the top to atmosphere, figure out a way to connect the throttle control to the slide, and block the butterfly wide open. Especially at first, I think I would want to remember carefully where the kill switch is.
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