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YS 91SR S Operator's Manual

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1

2

3. Tube(C) should be set exactly at 3 15/16” or (10cm)

between the engine and check valve. DO NOT use

any other type of check valve. The check valve is

designed exclusively for the 91SRS.

4. Adjust your throttle linkage and curve using the align-

ment indentations on the carburetor body located on

the throttle arm side of the carb body.

PLEASE NOTE that the hover position is at 40% see

FIG 2.

START UP

1. AlwaysremoveTube(A)atthecheckvalverstbefore

fueling. The fuel tank is pressurized and you need to

relieve the pressure first. Disconnected Tube(B) at

 thelterandllthetank.ReconnectTube(A)and(B).

2. From the fully closed (clockwise) position, turn the

needle valves counter clockwise as follows.

STARTING SETTING / OPERATING SETTINGSTARTIN

●

Hover 1.75 open 1.75 ~1.50

●

Low 1.25 open 0.75 ~0.50

●

Full 1.25 open 1.25 ~0.75

3. Close the throttle to the idle position and connect the

glow plug driver. The engine is now ready for starting.

SPECIFICATIONS

Bore 27mm

Stroke 26mm

Displacement 14.89cc

Weight 553g

Practical rpm 2,000 ~17,000

OPERATOR’S MANUAL

91SR S

(Helicopter Engine/ Part No.YS0074)

FEATURES

The 91SRS is the latest in helicopter engine technology

from YS.

●

New stroke design for superior operation

●

New carburetor design for easier adjustments.

●

Factory preset fuel regulator.

CAUTION

Using gear ratios higher than 9.0 to 1 may result in en-

gine damage from overspeed.

GEAR RATIO

You should be using an engine to main rotor gear ratio

of 1-7.5 to 1-8.0. Please check with your helicopter man-

ufacturer to obtain the correct gear ratio.

INSTALLATION

1. The fuel lines should be connected to the fuel tank as

shown in the above figure. Be careful to install the

check valve in the correct direction. Since the tank is

exposed to high pressures, be sure that all connections

are tight to prevent pressures leakage.

2. Since the engine is sensitive to dirt in the fuel, a fuel

 ltermustbeused.(WerecommendtheYS1195fuel

 lter.)

BREAK-IN

It is not necessary to mount this engine on a set stand

for break-in. However, the engine should be adjusted

slightlyontherichsettingfortherstfewightstoinsure

proper break-in. Always use a good quality fuel which

contain 15 ~30% nitromethane and an oil content of 18

~23% low viscosity oil.

NEEDLE VALVE ADJUSTMENT

Idle, Hover and High needle valves all work the same

way. Turning the needles clockwise will lean the fuel mix-

tures and counter clockwise will richer the fuel mixtures.

1. Set needles as described in START-UP.

2. Start the engine and check idle. Adjust as needed.

3. Lift helicopter into a hover and check for the correct

rotor RPM recommended by the kit manufacture.

Once this is done take note of the amount of smoke

 beingproducedbythemufer.Themixtureiscorrect

for hover when there is a steady stream of smoke

being produced.

4. Land the helicopter for approximately 20~30 seconds.

Lift the helicopter into a hover again taking note of the

transition from idle to hover. If the engine exhibits a

large amount of smoke and the throttle response is

sluggish, you will need to adjust the idle and or the

hover needle leaner to achieved a smooth transition.

If the engine detonates and the smoke is inconsistent

or a small amount is produced, the mixture is too lean.

5. Thehighspeedneedlerenesthefuelmixturefor

forward flights without affecting the hovering adjust-

ment. After the engine is started and warmed up, lift

off into a hover and check that the engine is running

smoothwithagoodtrailofsmoke.Ifeverythingisne,

open the throttle and enter forward flight. Take note

of the amount of smoke like we did in a hover adjust-

ment. It is correct when you see a noticeable steady

smoke trail. Adjust the high-speed needle valve to ob-

tain slightly rich but consistent setting.

STOPPING THE ENGINE

1. Fully close the throttle barrel to stop the engine.

2. As soon as the engine stops running, be sure that a

fuel line clamp is used in Tube(B) to prevent fuel from

 owingintotheengine.

3. Onthenalightoftheday,thefuellineclampshould

be used to stop the engine in order to prevent rust

and corrosion.

FUEL AND GLOW PLUG

We have found that the fuel and glow plugs listed below

will give the best engine performance.

Fuel

Powermaster 30% Special Heli Blend

Cool Power 30% Special Heli Blend

Glow Plug _ YS #2 Enya #3 OS #8

IMPORTANT!

Silicone rubber is used in many parts of the YS engine.

Use only glow fuel of methanol for cleaning. Gasoline

and other volatile solutions will damage silicone if used.

WARRANTY

Strict quality control is implemented by our factory in all

phases,frompartsmanufacturingtonalassembly.

If performance deteriorates or a part fails due to a manu-

facturing error, YS Parts and Service will repair or re-

place the engine at no charge in the period of one year

from date of purchase.

Warranty does not cover normal

maintenance.Shouldtheenginebemodied,incorrectly

assembled or abused, there will be a normal charge for

parts and labor.

Fig.1

Fig.2

High speed 100%

Low speed 0%

Hover 40%

52mm

43.5mm 25mm

Hover Needle

Fuel Filter

Tube (B)

Tube (A)

Check Valve

Tube (C) 3 15/16"(10cm)

Low Needle

High Needle

Factory Set

Do Not Adjust

STARTING SETTING / OPERATING SETTING