User manual YS FZ91

[. . . ] Clearance adjustment should be done when the engine is cool. When the engine temperature is high, clearance is higher due to thermal expansion. The proper clearance setting should be at 0. 04-0. 1mm. The adjustment is achieved by loosing the locknut(fig. 3) and turning the adjusting screw. Tighten the locknut after the adjustment is achieved. [. . . ] Silicone rubber is used in many parts of the YS engine. Use only glow fuel or methanol for cleaning. Gasoline and other volatile solutions will damage the silicone if used. FEATURES The FZ91 is the most powerful 91 four cycle engine available. This engine offers many exclusive features that have been proven on other YS engines. Supercharged system with simplified structure to keep weight to a minimum while still retaining maximum efficiency. Air chamber that uses crankcase pressure coupled with a double throttle valve system which allows a bigger charge of fuel and air mixture to enter the intake valve for more power. Same proven piston design as the 140Limited which creates more crankcase pressure for a more consistent fuel flow to the regulator. Fuel injection system for superior throttle response. This system is unaffected by tank position or by the attitude of the model. PROPELLER INSTALLATION Due to the high torque of the FZ91 engine, we have equipped it with double locknuts for safety. Mount the propeller and tighten the rear nut. Next, tighten the front nut as shown in fig. 2. Select a good quality propeller that will turn in the 8, 000 to 11, 000rpm range. We recommend sizes 13~12-14, 13. 5~10-14, 14~10-14. LOW SPEED ADJUSTMENT This engine is equipped with a new low speed needle valve to adjust the mixture from low to mid throttle. This needle valve is located on the side of the throttle barrel opposite the throttle arm(fig. 1). Open the low speed needle to 1 1/2 turns from fully closed position. The low speed needle valve should be set after the high speed needle valve has been adjusted. Close the throttle gradually to a idle(approximately 2500rpm). Let it idle for 20 to 30 seconds and then slowly advance the throttle. The adjustment is satisfactory at low speed if transition is smooth at this time. If the engine is running rough on idle, the low speed mixture is rich. If the engine starts to speed up and dies on idle or starts to detonate, when advancing the throttle, the mixture is lean. Turn the low speed needle valve clockwise to richen and counterclockwise for a leaner mixture(note that the direction of the low speed needle valve is opposite the high speed needle valve). [. . . ] Pour several drops of fuel into the carburetor. Close the throttle to the idle position and connect the glow plug cord. The engine is now ready for starting. INSTALLATION . Connect the engine to the tank as shown in fig. 1. [. . . ]