I recommend that you get a book on Rochester carbs, there are several out there. I will have to look at the exploded diagram of that carb when I get home to find the powervalve. They are slightly differant in each case. It generally consists of a small springloaded piston connected to either a valve or a metering jet. It bypasses the main jet.

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A lone amateur built the Ark. A large group of professionals built the Titanic.