6
ENGINE PREPARATION
Yokomo 18 engines are compatible with most aftermarket engine parts (muffler, plugs, air filters, etc.) that fit OS engines. We recommend
an OS #8 glow plug, a foam-type air filter (Yokomo #ZE-656), and a muffler that has a fitting to provide pressure to the gas tank.
FUEL
Use fuel designed specifically for R/C cars. Do not use fuels blended for R/C plane or boat engines.
ENGINE BREAK-IN
Proper break-in of this engine is very important. The engine can be destroyed if broken-in improperly. It is very important that THE CAR NOT
BE DRIVEN FOR THE FIRST TANK OF FUEL! Allow the engine to idle while set extremely rich for the first tank of fuel. After the engine has run
through a full tank of fuel at idle, drive the car very slowly for the next 3 to 4 tanks. Make sure that the carburetor is set very rich to allow
extra cooling and lubrication while the piston is breaking-in. The muffler pipe should emit a blue/white smoke at full speed. After the break-in
period and 10 tanks of driving, the engine will be MUCH FASTER! So be patient, and allow the engine to be broken-in properly.
PULL STARTER
Pull about 12” each time to prevent the rope from breaking. Do not pull the rope out completely. If an electric starter box is used, it MUST
spin in the proper direction to prevent damage to the pull starter. Accidentally spinning the flywheel in the opposite direction will damage the
pull starter!
BREAK-IN SETTINGS
AFTER BREAK-IN
NEEDLE VALVE
(Adjusts high speed air/fuel mixture)
Turn the needle valve 2 to 4 clicks CLOCKWISE
(lean) until the exhaust smoke is light at high
speed under load.
If you do not see exhaust smoke at high speed,
turn the needle valve 2 to 4 clicks COUNTER
CLOCKWISE to richen the mixture.
The normal needle valve setting for a fully
broken-in engine is between 1 1/2 and 2 1/2
turns.
NEEDLE VALVE
(Adjusts high speed air/fuel mixture)
2 1/2 TURNS COUNTER-CLOCKWISE from closed.
To find the fully closed position, slowly rotate
clockwise until it stops.
Do not try to turn the needle valve once it stops
(forcing it beyond this point can damage the
needle valve.)
IDLE ADJUSTMENT SCREW
(Adjusts engine speed at idle)
With the throttle lever in the 'closed' position, turn the
screw 1 1/2 TURNS CLOCKWISE from 'slightly open' throttle
opening. The opening should be about 1.5mm or .07".
THROTTLE LEVER
(Opens/closes carburetor)
When starting the engine,
adjust the throttle-trim on
the radio to set the throttle
lever at 20% open to provide
extra fuel when starting the
engine.
These settings will provide a good starting point for breaking-in the engine. During break-in, the exhaust should always
emit EXCESSIVE blue/white smoke. Remember that new engines may be difficult to start because the piston and sleeve
have not broken-in yet. If the engine is too rich and cannot sustain an idle, it may be necessary to lean out the needle valve
a few clicks CLOCKWISE if the engine is too rich.
IDLE ADJUSTMENT SCREW
(Adjusts engine speed at idle)
If the engine idles too fast with the throttle lever fully
closed, turn the idle adjustment screw 1/4 turn COUNTER
CLOCKWISE to close the opening slightly.
THROTTLE LEVER
(Opens/closes carburetor)
Adjust the throttle servo trim
to adjust idle speed.
The optimum settings for the carburetor will depend on the fuel, glow plug, muffler pipe, weather, etc. We recommend that
the engine always be tuned slightly rich to prevent overheating and damage to the piston and sleeve. Always look for a
slight amount of exhaust smoke to indicate a slightly rich mixture.
MAINTENANCE
Proper maintenance will extend the life of the Yokomo 18 engine. The air filter should be cleaned or replaced frequently. Use new fuel whenever
possible. Old fuel is likely to have absorbed water, which may cause erratic engine operation. After you have finished driving, remove all fuel from
the tank and fuel line and use an 'after-run' oil to prevent internal corrosion. Use denatured alcohol to clean the exterior.
