Demon Fuel Systems 5563020GC - Manual (Page 9)

9
Curb Idle Speed and Mixture Adjustments
Fine tuning of the idle speed and mixture must be done with the engine at or near operating
temperature. A good rule of thumb is to not attempt adjustments until the engine has achieved 160
degrees water temperature. Adjusting the engine cold will usually result in a rich mixture at normal
operating temperature. It is also helpful to use a tachometer and/or a vacuum gauge for setting the
idle speed and mixture.
If you have set the butterflies open for fast idle during warm up, return them to their original closed
position as discussed in the preliminary set up instructions. If the engine stalls as you close the
butterflies, it is usually an indication of a lean idle condition. Turn all 4 mixture screws out 1/4 to 1/2
turn from the start up setting and re-fire the engine. Also check to be sure that with the engine idling,
there should be no fuel visible dripping from the venturi boosters. If fuel is visible from the boosters,
then the floats may be too high, the butterflies are still too far open, or the fuel pressure is too high.
Do not attempt to correct the idle mixture until the necessary adjustments have been made to stop
fuel flow from the boosters. You may now evaluate the adjustment of the idle mixture screws.
Adjusting the idle mixture usually takes two or more trips around the car. Turning the screws in,
clockwise, reduces the amount of idle fuel and leans the idle mixture. Backing the screws out
increases idle fuel and enriches the idle mixture.
Begin by turning each screw in 1/8 to 1/4 turn at a time. If idle speed decreases, back the screws out
1/8 to 1/4 turn. If idle speed increases, adjust them in again. Adjusting the screws to less than 1 full
turn open can result in an off-idle stumble. However, some engines may respond well and not
stumble with less than one turn.
The goal for best idle quality and throttle response is to have the engine idle with the butterflies
closed, at the correct RPM, with the highest manifold vacuum, and the mixture screws adjusted
between 1 and 2 -1/2 full turns out from fully closed. Again, your particular combination may function
correctly outside of this range.
If you have any further questions concerning the tuning of your carburetor, please contact the tech
staff for more information.
Fuel Pressure
Most gasoline powered engines usually require between 6 and 7-1/2 PSI fuel pressure. Gasoline
carburetors can be run either at idle or wide open throttle at these pressures. Be sure your fuel
delivery system is properly adjusted and able to maintain volume flow at these pressures. Improperly
adjusted or inadequate fuel delivery will result in poor performance and possible engine damage.
General Tuning and Component Information
Once you have completed the initial installation, and preliminary adjustments, you are now ready to
test the vehicle and evaluate any other possible tuning adjustments. Information on changing the
configuration or fuel metering of your Demon is also included in this section.