how to adjust Rochester Carb?
Race Director
Joined: Jun 2000
Posts: 10,051
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From: FL
Re: how to adjust Rochester Carb? (poweredbylt1)
This is a very open ended question. Are you running lean at cruise or under wide open throttle? Not enough information given.
On the Q-Jet, the primaries control part throttle/cruise fuel flow with a combination of metering jets and rods. The rods are controlled by vacuum and the difference between the jet and rod areas controls cruise fuel flow. Under acceleration, the rods are fully withdrawn under just the primary jet size controls fuel flow. As rpm and air demand increases, the springloaded secondary airvalve door will open. As this happens, the secondary metering rods are raised which allows fuel into the secondary side of the carb.
This is a very simplified explanation which gives you some idea of the complexity of the Q-jet. I highly recommend getting both the book Rochester Carburetors by Doug Roe (try Amazon) and a copy of Lar's Q-jet tuning paper (available at http://www.corvettefaq.com). These references will definitely help you out.
Probably not the answer you were looking for, but the best I can offer.
On the Q-Jet, the primaries control part throttle/cruise fuel flow with a combination of metering jets and rods. The rods are controlled by vacuum and the difference between the jet and rod areas controls cruise fuel flow. Under acceleration, the rods are fully withdrawn under just the primary jet size controls fuel flow. As rpm and air demand increases, the springloaded secondary airvalve door will open. As this happens, the secondary metering rods are raised which allows fuel into the secondary side of the carb.
This is a very simplified explanation which gives you some idea of the complexity of the Q-jet. I highly recommend getting both the book Rochester Carburetors by Doug Roe (try Amazon) and a copy of Lar's Q-jet tuning paper (available at http://www.corvettefaq.com). These references will definitely help you out.
Probably not the answer you were looking for, but the best I can offer.
