Tube (A)
High Speed Needle
Low Speed Needle
Check Valve
YS Fuel Filters
(YS1195/not included)
Tube (B)
112.5
25
63
128
58
FEATURES
The YS140 Limited was developed for the serious competitor in mind.
As aircraft increases in size, so does the need for power. With a few
modifications internally, YS was able to generate more power in the same
140 case. The YS 4 cycles are so unique, almost every square inch is
used in some way to produce power.
* Supercharged
* Fuel Injected
* Regulated and Pressurized Fuel System
* High and Low Speed Adjustments
GLOW PLUG
Select the most appropriate glow plug from those designed specifically for
4 cycle engines. Glow plug selection greatly affects the maximum engine
output and low idle. If RPM’s decrease or stop when the booster cord is
removed, replace the plug. We recommend The YS #4 or the OS Type F
plug for maximum performance.
INSTALLATION
1. Connect the engine to the tank as shown in fig.1. Since high pressure
is applied to the tank, tighten all connections carefully. Care must be
taken to prevent pressure leakage due to undertightening of the check
valve or by kinking the fuel lines.
2. Always use a fuel filter. We recommend YS filter.
3. Match the direction of the check valve arrow in fig.1, with the arrow
facing towards the tank.
PROPELLER INSTALLATION
Due to the high torque of the140L engine, we have equipped it with
a double locknut system for safety.
1. Mount the propeller and tighten the rear nut. Next, tighten the front nut
as shown in fig.2. The rear nut has a offset shoulder so the front nut
will secure itself to the rear nut.
2. Select a good quality propeller that will allow the engine to run at
maximum speed between 8,000 to 9,000rpm range. We recommend
sizes 14x14,(15x12 through 14),(16x11 through 14).
START UP
1. Remove tube A from the check valve, (CAUTION) Tank pressure must
be release first before tube B is opened. Remove tube B and begin to
fill fuel tank.
2. Open the high speed needle 2 1/2 turns from the closed position.
3. Open the throttle fully and slowly turn the propeller 10 times. This will
prime the engine and pressurized the fuel tank.
4. Close the throttle to the idle position and connect the glow driver.
The engine is now ready for starting.
DO NOT ATTEMPT TO START ENGINE AT FULL THROTTLE, AS THIS
IS VERY DANGEROUS. ALWAYS USE EXTREME CAUTION WHEN
ENGINE IS RUNNING.
BREAK-IN
To maximum engine performance and increase durability, please follow
this break-in procedure.
1. Use the same size (or slightly smaller) propeller than you intend to
use in flying.
2. Use a good quality fuel which contain 15-30% nitromethane and an
oil content of Low Viscosity oil 20-24% oil. Synthetic or castor oil can
be used, or a combination of both.
DO NOT USE FOUR CYCLE FUEL DUE TO LOW OIL CONTENT.
3. After the engine has started, slowly bring the throttle up to full.
Set high speed needle so it is running at a good rich setting without
the glow driver. Run engine at this setting for approximately 20
minutes with the throttle moving from low to high speed.
4. After the initial 20 minute break-in, mount the engine in the aircraft
and set the high speed to a richer than normal setting for the first 10
flights. This will help to lubricate all moving parts.
HIGH SPEED NEEDLE ADJUSTMENT
1. Adjustment of the high speed is done by the carburetor needle valve.
When the needle valve is turned clockwise, the mixture is leaner. When
it is turned counterclockwise, the mixture is richer. A good starting
position for the high speed needle valve is 2 1/2 turns open from the
fully close position.
2. When the engine is started, open the throttle gradually. Next, find the
peak position (highest RPM) by adjusting the needle valve. Then the
needle valve should be opened approximately 1/8-1/4 turns from
full RPM to achieve best performance. The engine may stop if the
throttle is opened to full immediately after starting. Wait until the
engine has warning up and pressure has developed in the tank.
LOW SPEED ADJUSTMENT
This engine is equipped with a new low speed needle valve to adjust the
mixture from low to mid throttle. See fig.1 for location.
1. Factory starting position is 1 1/2 turns open from the fully closed
position. The low speed needle should be set after the high speed
needle has been adjusted.
2. Close the throttle gradually to an idle (approximately 2,000rpm). Let it
idle for 15-20 seconds and then slowly advance the throttle.
The adjustment is set when low to high speed has a smooth transition.
3. If the engine is running rough at idle or to rich, turn the low speed
needle counterclockwise to lean out the low end.
4. If the engine speeds up at idle , the low speed mixture is to lean.
Turn the low speed needle clockwise to richen the mixture.
5. If the engine is to lean on the low end, it can detonate and stop when
transition from low to high RPM.
REGULATOR ADJUSTMENT
The regulator is preset at the factory. The top of the brass adjusting screw
is flush with the top of the regulator housing. Turning the regulator screw
will not change the pressure the engine develops. The adjustment screw
is used to adjust the amount of fuel to the carburetor. Turning the screw in
will decrease the amount of fuel and turning the screw out will increase
the amount of fuel to the carburetor.
SPECIFICATIONS
Bore
32mm
Stroke
29.0mm
Displacement
23cc
Weight
890g
Practical rpm 2,000 -12,000rpm
TAPPET ADJUSTMENT
Tappet clearance is preset at the factory. Adjustment if needed should be
checked after the initial break-in. For maximum performance, valves should
be checked as normal maintenance.
1. Clearance adjustment should be done when the engine is cool.
2. The proper clearance should be set 0.04-0.1mm or 0.002-0.004 in.
The adjustment is achieved by losing the locknut (fig.3) and turning
the adjustment screw. The engine must be at top dead center on the
compression stroke before any adjustment are made.
CAM GEAR TIMING
If for some reason you have to disassemble your engine, please follow
these important steps on reassembling the cam gear.
1. Remove the carburetor and backplate assembly. Notice the
impression mark or dot opposite the rod journal on the crankshaft. This
mark is to point straight down or lined up with the outer case seam line at
the bottom.
2. Reinstall the cam with the dot facing you and is pointing slightly to the
left. This will allow the cam to turn to the right when properly installed.
The dot should be pointing starting up when cam is fully installed.
Reinstall cam cover and timing is now set.
DIAPHRAGM AND CHECK VALVE DISASSEMBLY
Diaphragm;
1. Remove the regulator assembly by removing the two aline head screws.
2. Disassemble the regulator and clean with alcohol or appropriate cleaner.
3. When reinstalling the regulator, use a new gasket and note that the
small casting tab on the regulator goes towards the propeller.
Check Valve;
1. Open the check valve by rotating the body counterclockwise.
Note the small clear silicone disc. DO NOT LOSE.
2. Clean and reassemble. Check to make sure air will only past though
the check valve one way.
IMPORTANT!
Silicone rubber is used in the YS engine. Only use glow fuel or methanol
for cleaning. Gasoline and other volatile solutions will damage the sili-
cone if used. Do not use petroleum based oils as after run lubricants.
OPERATOR’S MANUAL
140Limited
Supercharged (Part.No.YS0095)
fig.1
fig.2
fig.3
Front Nut
Rear Nut
Tappet Clearance
WARRANTY
Strict quality control is implemented by our factory in all phases, from parts
manufacturing to final assembly. If performance deteriorates or a part fails with-in
one year of purchase due to a manufacturing error,YS will repair or replace the
engine at no charge. Warranty will not cover normal wear.
Should the engine be modified or incorrectly assembled, there will be a normal charge for
parts and labor. The use of four cycle fuel due to low oil content will also void warranty.
