Quick Set Adjustable
Vacuum Secondary Housing
Installation and Tuning Instructions
1. Remove old vacuum secondary housing. Note: If your carburetor is equipped with a
choke it will be necessary to remove the choke housing and assembly to access all the
screws securing the vacuum secondary housing.
2. Install new vacuum secondary housing. A new vacuum passage gasket has been
cemented in place, check to be sure it is still positioned correctly.
3. Tighten all three screws to secure new vacuum secondary housing is place. Do not
over-tighten these screws! Use a small, short screwdriver to avoid over-tightening.
Reassemble and reinstall choke housing and assembly in reverse order of
disassembly. If you experience any problems or difficulties, consult a service manual
4. Baseline setting for the adjustable needle is 1 1/2 turns off the seat, this setting has
already been made during assembly at our facility. Should you ever need to re-
establish your needle setting, lightly seat the needle. Do not over-tighten as this will
alter the seat taper and could change the performance characteristics.
5. The Quick Set Adjustable Vacuum Secondary Housing incorporates a “Purple”
spring. This ensures the secondaries will open fully on most applications. The
purpose of the adjustment screw is to vary the opening rate, that is, when the
secondaries begin to open as well as how quickly they open.
6. The secondary diaphragm operates off venturi vacuum. As airflow increases through
the primary side of the carburetor, a vacuum is created in the venturi. It is this
vacuum signal that actuates the secondary diaphragm. Without an accelerator pump
on the secondary side of the carburetor it is necessary to graduate the secondary-
opening rate. Air responds instantaneously when the throttle plates open, however,
there is a delay before the fuel begins to flow.
7. For best performance you should not “feel” the secondaries opening. If you “feel” the
secondaries open, do not confuse this feeling with better performance. That feel is
actually a hesitation or a bog. Simply stated, the increased airflow has insufficient
fuel to make a combustible mixture.
8. Best performance therefore is accomplished by determining what needle position
creates a hesitation. Then gradually turn in the adjustment needle in 1/8-turn
increments until the hesitation is eliminated. This will provide the optimum wide-
open throttle acceleration.
9. The Quick Set Adjustment will allow you to tune for variations in traction, weather
conditions, etc. How your engine responds to these conditions will determine where
the adjustment screw should be set. This will require experimentation on your part;
however, the Quick Set Adjustment will enable you to achieve the best performance
possible under all conditions.
Quick Fuel Technology
129 Dishman Lane
Bowling Green, KY 42101
1-270-793-0900
P/N 99-19
©Quick Fuel Technology 2002
(1 pages)
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