FUJI-IMVAC BT-5SB Operator’s Manual

Operator’s Manual for BT-50SB

SPECIFICATIONS

Displacement: 2.84 cu in [46.5cc]
Horsepower: 5.2 hp @ 9,000 rpm
Ignition Style: CDI Automatic

Timing Module

RPM: 1,200 – 9,000 rpm
Fuel: Gas/2-cycle engine oil
Weight w/muffler: 4.8 lb [2.2kg]

Manufactured by FUJI-IMVAC INC.

YOKOHAMA, 235-0005 JAPAN

Worldwide Distributor (except Japan): Hobbico, Inc.

Champaign, IL 61826 USA

www.fuji-imvac.com

Fuji-Imvac is not related to the original Fuji Engines sold by Mecoa.

™

SAFETY TIPS AND WARNINGS

Always use a balanced spinner and a balanced prop. An unbalanced spinner

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and prop combination will cause high levels of vibration and may cause the
propeller shaft to break.

Always use a lightweight spinner on your engine. Lightweight spinners are

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considered to be those with a cone wall of 1mm or less. Heavy spinners could
cause the propeller shaft to break.

Securely tighten the spinner and prop on the engine to prevent it from being

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thrown off the engine while running.

Never use a prop that has hit the ground. Even though it may look good from the

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outside, it may be cracked on the inside which may cause it to disintegrate while
in use. Do not use a nicked, cracked or split propeller.

Keep foreign objects away from the propeller. Make sure that nothing can be

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“sucked in” by the propeller. Never start the engine on loose gravel or sand.

Keep onlookers away from the running engine, especially small children.

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Do not attempt to stop the engine by throwing anything into the path of the propeller.

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Make sure the fuel line is well-secured to the engine and to the fuel tank so that

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it won’t come off in flight.

Do not use silicone fuel line because it will be attacked by the fuel. Use vinyl or

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neoprene rubber fuel line.

Always secure the fuel line away from the cylinder head. The engine’s heat can

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damage the fuel line.

Never touch the engine after a run. The engine will be hot and it may burn you.

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Before transporting your model, remove all the fuel from the fuel tank and fuel lines.

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Always use high quality oil intended for 2-cycle engines.

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Use only low-octane, alcohol-free gasoline. The carburetor diaphragm will

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gradually deteriorate if you use gasoline with alcohol. You will need to replace
the diaphragm in about 80 hours of operation if you use gasoline with alcohol.

Muffler pressure to the fuel tank is not required.

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Do not install your throttle servo or kill switch servo inside the engine compartment.

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Doing so could cause radio interference. Install all electronic radio devices at least
12" [305mm] away from the engine. The throttle pushrod should be non-metallic.

In case the engine is not to be used for more than a month, drain the fuel tank

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and remove any fuel from inside the carburetor. Do this by running the engine
at idle until it quits by running out of fuel. Keeping gasoline inside the carburetor
over an extended period of time will damage the diaphragm valve and clog
passages inside the carburetor.

Because the carburetor is more complicated than those used in glow engines,

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keep the fuel clean by using a fuel filter. Use a filter intended to be used with
gasoline engines. Metal filters intended for glow engines are too coarse and will
not screen out finer particles. Always filter your fuel by using an appropriate filter
before putting it into the airplane’s fuel tank.

If you intend to run this engine on an engine stand, or on any other rigid mount,

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use rubber mounts. The crankcase and other parts of the engine may crack if
you do not provide some kind of vibration absorption mechanism. A rubber
mount is not necessary if the engine is mounted on a model airplane.

Do not operate the engine in a closed room or where ventilation is not adequate.

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Gasoline is extremely flammable. Keep it away from an open flame, excessive

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heat or sources of sparks. Do not smoke near the engine or the fuel tank.

This engine was designed for use in a model aircraft. Do not attempt to use it

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for any other purpose.

Always install a kill switch that can be operated both manually and with the RC

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transmitter.

AUTOMATIC IGNITION TIMING MODULE

The BT-50SB engine ignition system is a combination of an electronic system and
a mechanical system. The working principle for the Automatic Timing Module is that
it gradually advances the ignition timing as the ignition pulse increases with
increasing engine rpm. The mixture is ignited when the piston is near top dead
center for idling and the timing is gradually advanced as the rpm increase.

PREPARING THE ENGINE

1. Check to see that all screws and bolts are tight. Check carefully for any cracks,
broken or missing parts. Tighten or replace before proceeding.

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2. Install the prop shaft on the flywheel.

3. Install the spark plug in the cylinder head.

SPARK PLUG

The recommended spark plug is a Champion RCJ-6Y. To avoid improper operation
or possible engine damage, do not use any other type of spark plug. The plug gap
should be 0.016" to 0.024" [0.4mm to 0.6mm]. If the plug gap is incorrect, adjust
it with a spark plug gapping tool, wash it with gasoline and allow it to dry
completely before you reinstall the plug in the engine.

PROPELLER

Always use a well-balanced, high-quality propeller.

The recommended propellers are:

18" x 10", 18" x 12", 20" x 8", or 20" x 10"

High Performance Wood Prop

20" x 10" or 21" x 10" Carbon Prop

During our tests, our Fuji-Imvac BT-50SB turned a Bolly 20" x 10" carbon prop at
7,600 rpm. The engine was new with 90 minutes of breaking in. The test conditions
were: Temperature 50°F [10°C], Humidity 40%, elevation at sea level. Performance
may vary depending on atmospheric conditions.

INSTALLING THE FUJI-IMVAC BT-50SB ON YOUR AIRPLANE

Note: The Fuji-Imvac BT-50SB must be installed on a 1/2" [12mm] lite ply firewall
or on a 3/8" [9.5mm] birch ply firewall. The firewall must be securely glued to the
airplane. Use triangle stock and pin the firewall with hardwood dowels to reinforce
the firewall glue joints. Never install the Fuji-Imvac BT-50SB onto a firewall thinner
than specified because it may fail due to the power of the engine.

1. Use the supplied template (on the back cover of this manual) to drill the engine
mounting bolt holes and the necessary clearance hole on the firewall.

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2. Install the engine on the firewall using four 1/4" x 1-1/4" [6.4mm x 32mm] socket

head cap screws, four 1/4" [6.4mm] flat or lock washers and four 1/4" [6.4mm]
blind nuts. Use some threadlocking compound, such as Great Planes® Pro™
Threadlocker (GPMR6060), on the screws.

3. Install the fuel tank in the airframe. Use only gasoline-safe fuel lines. One line
should go to the carburetor and the other is to be used as a vent. You can fill the
tank by using the carburetor line as the fill line if you have access to it or install a
third line to be used as the fill line.

4. Install a kill switch such as the Great Planes Gas Engine Ignition Switch Harness
(GPMG2150). Install the kill switch servo at least 12" [305mm] away from the engine.

5. Install the throttle servo at least 12" [305mm] away from the engine. Make sure
that you get the carburetor's full range of rotation with your servo travel.

6. Cut all necessary clearance and cooling holes in the cowl.

7. Make sure the cowl is secured to the airplane and that the spinner to cowl

clearance is at least 1/8" [3.2mm].

BEFORE OPERATION

1. Prepare only the amount of gasoline needed. Aged gasoline could damage the
engine and cause it to overheat.

2. If the engine was just run, make sure you allow enough time for it to cool down
before you run it again. Also, wipe any residue the engine may have thrown on the
airplane on the previous flight.

3. Check to see that there are no foreign objects in the path of the propeller.
Secure any loose articles of clothing so they cannot be drawn into the propeller.

4. Go through the safety tips and warnings at the beginning of this manual to
ensure a successful and safe engine run.

5. Fuel the airplane with the adequate gasoline mix.

BREAK IN THE ENGINE

To break in your Fuji-Imvac BT-50SB you need to run the engine for about one

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hour with a fuel mixture that contains a 25:1 (4% oil) fuel/oil ratio.

Do not adjust the high-speed needle on the carburetor to break in the engine. If you

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do so, carbon will accumulate in the spark plug and that will make ignition difficult.

Do not run at full power for extended periods of time while breaking in your engine.

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Make sure that the engine has adequate cooling. While breaking in, the engine

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may run at slightly higher temperatures.

If you wish to do so, you can break in your Fuji-Imvac BT-50SB while flying your

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airplane. Just make sure you observe all recommendations above.

RUNNING THE BT-50SB ON YOUR AIRPLANE.

Once the engine is broken in, use 40:1 (2.5%) fuel/oil mix.

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