Demon 625 Street Demon Carburetor 1900 Instruction Manual
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Contents
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9The idle mixture screws are preset at the factory and SHOULD NOT need any adjustments, however some engines mayrequire more or less fuel at idle. To adjust the idle mixture, begin by lightly seating both screws and then turning out 2 fullturns as a beginning point. Next, turn each screw in 1/8 to 1/4 turn at a time alternating between each screw. If idle speeddecreases, back the screws out 1/8 to 1/4 turn. Turn them equally until you achieve the highest possible manifold vacuumor highest idle RPM reading. Adjusting the screws to less than 1 full turn open, can result in an off-idle stumble. Once youridle mixture screws are adjusted properly, you can now adjust the idle set screw to achieve the desired idle RPM (Fig. 10).Figure 9 Figure 10Fuel PressureDemon recommends between 5 and 6 PSI fuel pressure at idle. Gasoline carburetors can be run either at idle or wideopen throttle at these pressures. Be sure your fuel delivery system is properly adjusted and able to maintain volume flowat these pressures. Improperly adjusted or inadequate fuel delivery will result in poor performance and possible enginedamage.Complete the following steps to tune the electric choke:Figure 11 Figure 12 Figure 131. There are two primary adjustments: the fast idle adjustment screw and the choke timing. The fast idle adjustmentscrew controls how far the primary butterflies are open when the choke butterfly is closed or partially closed. Itcontrols how fast the engine will idle during cold engine warm up. The fast idle adjustment screw is located on thebracket that is screwed to the throttle shaft, behind the choke housing (Fig. 11). Fast idle can be increased by turningthe fast idle screw clockwise, or decreased by turning it counter-clockwise. It is important to note that when the chokebutterfly is open completely (vertical up and down), the fast idle adjustment screw must not be holding the primarybutterflies open at all. In other words, when the fast idle adjustment screw is at the lowest step on the fast idle cam, itmust not be touching (or making contact) the fast idle cam. See Figure 12 for a view of how the fast idle screw rideson 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 securethe choke cap to the choke housing (Fig. 13). Rotating the choke cap clockwise will decrease the amount of time ittakes the choke to open, while counter-clockwise will increase the time it takes. This adjustment will depend on yourclimate and the vehicle it is installed on. The factory setting can be referenced by making note of where the indexmark is positioned in the cap in reference to the marks on the casting.3. The 14” Demon air cleaner (Part # 786004) is designed to clear the choke plate linkage on all Demon carburetors. Ifyou use another brand of air cleaner / air cleaner gasket or air cleaner spacer, it is necessary to make sure that thefull range of motion of the choke shaft and butterfly are realized. Failure to do so could result in the choke not |
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