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Old 07-27-2008, 10:05 AM
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More critical detail. At WOT hi boost, the blower can and will pull so hard on the carb that a vaccuum can/will be created just under the carb at high rpm max load.
The power piston and step up spring that controls the primary metering rods ( cruise/power circuit) reacts to any vacuum under the carb. On a N/A motor it does what it is supposed to do. But on draw thru supercharger system like yours the power piston can get fooled into going lean at the wrong time High rpm WOT max boost. So, you must install a vacuum guage and read the vacuum at the carb base at full throttle max rpm. If the power step up spring gets pulled down in its bore (lean) bad things will happen. Select a power step up spring with enough tension to prevent it from being pulled down (lean) at WOT max rpm.
There are various edelbrock QJET power piston springs of various vacuum ratings to select from. If say you get 4" of vacuum under the carb at WOT high rpm then use a spring rated higher 6" 7" or 8" or so.
Usually on these blowers once the power piston spring is propely selected a boost referenced power piston is not nessessary.

This is a critical must do calibration modification when using a QJet with a blower.
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