Instructions for
FK 50 (no. 250, 250g)
In order to enjoy many years of flying with your KAVAN FK 50 engine, we recommend you to follow the operating instructions carefully. (read safety instructions)
  Mount the engine on a heavy duty test bench (solid table which will hold up to the power of this engine; add weight if necessary). Install a fuel tank (500 ccm/16 oz - No. 31A) directly behind the engine, at the same height as the carburetor. Be sure to use an in-line fuel filter (No. 19). Attach a pushrod to the carburetor arm and clamp it so that constant throttle settings can be maintained.

  The lubrication system of the KAVAN FK 50 is the same as that used in full scale engines. The inner parts of the engine are lubricated by an oil pump channeling oil from the sump to all movable parts. During inverted flight, lubrication of the connecting rod is assured through the downward flow of engine oil.

  A knurled, slotted screw, attached to the dip stick, is installed in the crankcase behind the left cylinder. Remove this screw and pour 30 ccm (1 oz) of four-cycle motor oil into the sump. Using the enclosed injection syringe will simplify this procedure. While the oil level should not be lower than indicated on the dip stick (lower mark on the stick), a maximum amount of 30 ccm (1 oz) should not be exceeded. When checking the oil first remove the dip stick, clean it and dip it into the oil completely. During engine break-in, the oil level must be checked after using the contents of one fuel tank, or after 15 minutes of operating time.

  As the FK 50 has a separate lubrication system, we recommend a fuel consisting of high quality, water-free methanol with 2% oil. During engine break-in (4 to 5 operating hours) no other oil but degummed AAA castor oil may be used. To use any other oil but degummed AAA castor oil (for example synthetic oils) will void the warranty.

After the engine break-in you may use synthetic oils (high quality only[), also for the oil sump, instead of castor oil in order to achieve a good mixture. Before stopping the engine you should run it at full throttle for at least a minute in order to prevent damage from corrosion inside the FK 50.

  A pressure relief valve, for crankcase ventilation, has been installed in the front part of the crankcase forward of the front bearing. The white plastic cover, which serves as protection for the pressure relief valve during transportation or storage, has to be removed prior to starting the engine. This pressure relief valve must not be sealed during operation. Keep the length of the air relief tube (silicone) as short as possible. Tile diameter of the air relief tube should be as large as possible - at least 3 mm ('0.1 '~) - so that the pressure inside the crankcase can escape.

  For long life and high performance the FK 50 requires the correct breaking-in procedure. All movable parts are manufactured from wear-resistant, hardened material and need an extended period of break-in. Not only the compression rings have to be run-in properly, also the important oil scraper-rings have to create their own cylinder path with a sealing effect. For breaking-in the engine, we recommend the propeller 20 x 10" (No. 333,252C). After the engine has been run in, end while it is still warm, retighten the screws and nuts on the flanges and crankcase because the screws and gaskets will be set due to the heat, and thus, the screws and nuts tend to loosen.

  Fill the fuel line and prime the engine by choking the carburetor intake with your finger and turning the propeller a few items towards the left; an engine primer bottle (No. 25) may be used instead if preferred. Close the carburetor barrel leaving an opening of approximately 1mm (0.04"). Connect both glow plugs to the battery. When sufficient fuel has been' pumped into the engine and both glow plugs are hot, the engine will start immediately after flipping the propeller a number of times. Gradually apply more throttle (half throttle) and disconnect the battery after approximately 15 seconds of operating time. Do not concern yourself with the idle or full throttle at this time, but set the carburetor so that the engine will run at between 5,000 and 6,000 Rpm (during break-in a rich fuel mixture is preferable to a lean one).

  A certain amount of time is required to familiarize yourself with the functions of this carburetor. It is basically set and adjusted at the factory. Therefore you only have to very carefully make fine adjustments at the adjustment screw (5) (f/4 - f/2 turn: clockwise = leaner, counter. clockwise = richer). You should never turn the screws (4a, 5a), since they were already set correctly at the factory.

After a total running time of 5 to 6 tanks of fuel has been accumulated, you can gradually set the carburetor for maximum Rpm. Slowly turn the needle valve to the right. Before setting the idle speed, mount the propeller that is intended for later use. Various aspects influence the choice of propeller size: the size of the airplane, wing-profile, available space between ground and crankshaft, as well as altitude. As soon as the oil scraper-rings have been run-in, the oil consumption of the engine will reduce drastically.

KAVAN Carb Setting

As with most carburetors, the air intake is controlled by a rotary throttle valve. A rotary throttle valve adjustment screw (1) is used to set the carburetor for the idle position. This screw should be set in such a way that the throttle is just closed when set in the idle position (check by looking through the air intake). The air flow required in the idle position is then sucked in through the idle-air-intake or 'air-bleed' hole (2). The idle air adjustment screw (3) regulates the effective size of the air-bleed. The basic setting for the air-bleed adjustment is with the end of the screw halfway across the air-bleed hole.

The fuel supply of this carburetor, which was specially designed for the FK 50, is regulated by a curve-control-system. With the carburetor correctly fine-adjusted and the glow plugs disconnected, the engine should run at 1,800 Rpm. If the engine will operate only with both glow plugs connected, the mixture is too rich. For the following fine-adjustments, please use the long socket head screw wrench supplied. Loosen the lower clamp screw (4) of the curve-control-arm (6) (steel spring). For readjusting, turn only the small idle-adjustment-screw (5):

For leaner fine setting: clockwise.
For richer fine setting: counter-clockwise.

These adjustments will cause the lower curve-control-arm to slide out of, or into, the carburetor body and thereby reduce, or enrich, the fuel supply. When the desired idle setting has been reached, tighten the lower clamp screw (4) to prevent the idle setting from accidentally being changed. With every idle readjustment on the curve-control-arm, the needle valve must be reset (leaner or richer, respectively)

  We recommend the first oil change after running the engine for half an hour. Remove the magnet oil drain plug from the bottom of the sump, using a glow plug wrench, and let the oil flow out. The magnet portion of the oil drain plug collects fine metallic particles abraded during the engine break-in and should be cleaned with cloth material. After reinstalling the oil drain plug, pour another 30 ccm (1 oz) of multigrade automobile oil into the sump.

After operating the engine, the oil will mix with particles of soot, of castor oil and condensed water from methanol. Therefore, we recommend (to prevent damage from corrosion):

1. An oil change after each day of flying with this engine or, alternatively, after 2 to 3 hours of operating time. It is better to change the oil while the engine is still warm.

2. Following every flying session, be sure and let the engine run at full throttle for at least one minute so that any water that may have collected in the sump can evaporate. Then pull the fuel line and let the engine run out dry.

  Let the engine cool down and remove the valve covers (with inscription 'Continental') which will allow easy access to the rocker arms. The required valve clearance is between 0.04 mm and 0.10 mm (0.002" and 0.004"). An effort should be made to achieve the minimum clearance of 0.04 mm (0.002"). With each rotation of the crankshaft, one cycle takes place alternately in the left and right cylinder. When turning the engine by hand you will observe which valve does not move as the piston is at the top of the compression stroke, i.e. when both valves are closed. Now check this cylinder using a feeler gauge; the valve clearance can be corrected with the adjustment screws. Important: Tighten the lock nut M 3, check the valve clearance again, then secure the lock nut in place.

  Besides the oil change, as described above, it is also very important to check and adjust the valve clearance. The first checkup and/or adjustment should take place after 2 hours, the 2nd one after 5 hours and further ones after 10 to 15 hours of operation.

  Only factory authorized service representatives (see warranty card) should be entrusted with the disassembly of your FK 50. Unnecessary dismantling is not recommended for any type of model engine and should be avoided. If you like to disassemble your engine by yourself please note you are doing that at your own risk - to do so will void any claim for warranty.

  Due to its large displacement, the FK 50 has a strong suction capability. Make sure that the engine cowl is suitably vented to allow plenty of air to reach the carburetor intake, as well as providing a generous through-flow of air for cooling the engine. Exchange the plugs only by hand and very carefully in order to avoid a damage of the thread in the cylinder head.

  The KAVAN FK 50 engine with integrated spark-ignition system offers many advantages in operation, including easier starting, reliable idle, higher Rpm and reduced fuel consumption. The micro switch (No. 278), which is mounted on the carburetor, retards the spark (for starting and idling) and advances it for full power.

The ignition system employs a Hall Effect (magnetic) pickup (no points to burn, oil-up or get out of adjustment) and solid state components throughout and is very reliable.

We recommend the continued use of methanol/castor fuel (as specified in the instructions) rather than a gasoline-based fuel. It is cooler running, safer and gives more power and greater reliability.

1. The ignition coil (which also incorporates the electronics) must be installed on the left side of the engine (when viewed from the front) since the screened spark plug leads are of appropriately different lengths. The three-core (red/blue/black) lead from the coil must be plugged into the four-pin left socket of the distributor (again viewed from the front). The similar (red/blue/black) lead from the micro switch must be plugged into the right socket of the distributor. Please note that the leads should be routed so that they cannot come into contact with the exhaust pipe, otherwise

insulation will be damaged - which will cause a short-circuit. From time to time, the spark plugs should be checked and, if necessary, adjusted to a gap of 0.2 - 0.3 mm

2. Ground (earth) the brown wire to one of the upper screw-5 of the intake manifold.

3. A 4.8 volt 500 ma NiCd battery pack (sufficient for approximately 1 hour of running between charges) or 4.8 volt 1,200 ma (approximately 2 hours) is required. This is not furnished with the engine and can be obtained from your local hobby shop. The battery should be connected to the two-core (black/red) lead from the coil via a regular slide switch.



red wire to battery positive (+)

black wire to battery negative (')m

Warning: If you mix up the wiring, the electronics will be destroyed.

Note: The ignition system must be operated from its own, separate NiCd battery; do NOT connect it to the receiver battery! it is also advisable to keep the RC components (receiver, servos, battery, slide switch and wiring) as far away as possible from the ignition system.

4. Recheck all connections before applying power to the system - as already explained, an incorrect hookup will result in damage to the system.

5. The spark timing is factory-set before delivery. However, it may be adjusted as follows: Start the engine and let it run for approximately 5 minutes (engine must be warm for correct setting). You are behind the engine. While it is running, the timing can be adjusted by rotating the distributor a few degrees with the 3 mm (0.12'~ dia. steel rod supplied. Counter-clockwise movement 0.e. to the left - against the direction of propeller rotation) advances the spark; clockwise (to the right) retards it. It is not necessary to loosen the distributor retaining screws; the distributor will turn with steady pressure on the steel rod (an internal O-ring and sealing washers prevent accidental movement).

Adjusting the timing is simply a matter of advancing the spark to produce the highest full-throttle Rpm. Having adjusted the needle valve to its optimum setting, slowly turn the distributor against the direction of propeller rotation no further increase in Rpm is obtained, then turn it slowly back towards the "retard" position, but not so far as to cause Rpm to fall. This is the best running position. Experience has indicated that, at this position, the engine fires when the piston is approximately 1.5 - 2 mm (0.06 - 0.08") before top dead center. Please note that the engine revolutions at which the micro switch changes from advance to retard (and vice-versa) should be approximately 2,000 Rpm.


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