Demon Fuel Systems 4402020VE - Manual (Page 9)

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Changing the float level is accomplished by loosening the locking screw and rotating the adjuster nut
on the top of the bowl (Fig. 13). To prevent fuel leakage during the course of adjustments, only loosen
the locking screw enough to allow rotation of the adjuster nut. Rotating the adjuster nut clockwise will
lower the float level setting; conversely, rotating the adjuster nut counter-clockwise will raise the float
level setting.
It’s important to note that, although increased fuel levels are immediately visible in the sight glass,
lowered fuel levels are not. The excess fuel in the bowl must be consumed before the fuel level can
stabilize at the new lower setting. When lowering the float levels, allow the engine to run for a few
minutes, or gently rev the engine until enough fuel is used to establish the new lower setting. For this
reason, setting the floats a little low (
.500" or more) during the ‘dry setting’ procedure, then raising
them to the correct operating levels with the engine running, will prevent flooding at start up. It will
also shorten the time necessary to reach the correct setting. Experimenting with float settings a little
above or below the startup setting is also acceptable.
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 160º
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 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.