Demon Fuel Systems 1905 - Manual (Page 9)

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Ensure the engine is at idle with the choke fully open and at operating temperature. You may now evaluate the
adjustment of the idle mixture screws (Fig. 9). Turning the screws in (clockwise), reduces the amount of idle fuel and
leans the idle air mixture. Backing the screws out (counter-clockwise), increases idle fuel and enriches the idle air mixture.
The idle mixture screws are preset at the factory and SHOULD NOT need any adjustments, however some engines may
require more or less fuel at idle. To adjust the idle mixture, begin by lightly seating both screws and then turning out 2 full
turns as a beginning point. Next, turn each screw in 1/8 to 1/4 turn at a time alternating between each screw. If idle speed
decreases, back the screws out 1/8 to 1/4 turn. Turn them equally until you achieve the highest possible manifold vacuum
or highest idle RPM reading. Adjusting the screws to less than 1 full turn open, can result in an off-idle stumble. Once your
idle mixture screws are adjusted properly, you can now adjust the idle set screw to achieve the desired idle RPM (Fig. 10).
Figure 9 Figure 10
Fuel Pressure
Demon recommends between 5 and 6 PSI fuel pressure at idle. 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.
Complete the following steps to tune the electric choke:
Figure 11 Figure 12 Figure 13
1. There are two primary adjustments: the fast idle adjustment screw and the choke timing. The fast idle adjustment
screw controls how far the primary butterflies are open when the choke butterfly is closed or partially closed. It
controls how fast the engine will idle during cold engine warm up. The fast idle adjustment screw is located on the
bracket that is screwed to the throttle shaft, behind the choke housing (Fig. 11). Fast idle can be increased by turning
the fast idle screw clockwise, or decreased by turning it counter-clockwise. It is important to note that when the choke
butterfly is open completely (vertical up and down), the fast idle adjustment screw must not be holding the primary
butterflies open at all. In other words, when the fast idle adjustment screw is at the lowest step on the fast idle cam, it
must not be touching (or making contact) the fast idle cam. See Figure 12 for a view of how the fast idle screw rides
on the steps of the cam.
2. Rotating the black choke cap controls the choke timing. To rotate the choke cap, loosen the three screws that secure
the choke cap to the choke housing (Fig. 13). Rotating the choke cap clockwise will decrease the amount of time it
takes the choke to open, while counter-clockwise will increase the time it takes. This adjustment will depend on your
climate and the vehicle it is installed on. The factory setting can be referenced by making note of where the index
mark is positioned in the cap in reference to the marks on the casting.