3 If the engine is running rough at idle or too rich, turn the regula-
tor adjustment counter-clockwise to lean out the low end.
4
If the engine speeds up at idle, the low speed mixture is too
lean. Turn the low speed regulator adjustment clockwise to
richen the mixture.
TAPPET ADJUSTMENT
Tappet clearance is preset at the factory. Adjustment, if you needed,
should be checked after the initial break-in. For maximum perfor-
mance, 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 at not more than 0.002"
maximum. The adjustment is achieved by loosening the lock nut
( fig.3 ) and turning the adjustment screw. The engine must be
at top dead center on the compression stroke before any adjust
ments are made. This engine runs best with the valves set at a
tight setting. If the valves are set too loose ,power will be affected.
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 im-
pression 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 pointing slightly
to the left. This will allow the cam to turn to the right when prop-
erly installed. The dot should be pointing straight up when cam
is fully installed. Reinstall cam cover and timing is now set.
FUEL PUMP
I
f you must disassemble the fuel pump to change the diaphragm or
to clean, take care that the valves and springs are replaced in exactly
the same manner in which they were removed. Do not disassemble
the pump needlessly. Use care with filtering your fuel and keeping
the entire fuel system in good working order. It will help to prevent
fuel pump problems.
FEATURES
The DZ170 was developed for serious aerobatics competition and
large IMAC style aircraft. It differs from previous YS Engines in that
it does not use a high pressure fuel system but rather a true fuel
pump.
*Crankcase supercharging system unique to YS 4 stroke egines
*Fuel injected
*Convenient fuel pump adjustment
*High horsepower output with long service life
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 plug for
maximum performance. These are available from YS Parts & Service
or your favorite dealer.
INSTALLATION
WE RECOMMEND THAT THIS ENGINE BE MOUNTED ON A SHOCK
ABSORBING SOFT MOUNT
1 Connect the engine to the tank as shown in fig.1. The recomm-
ended fuel tank size is 18 to 24 oz. A standard clunk type fuel
tank may be used. If this type of tank is used, you must use the
special clunk supplied with the engine. Please note that with
this clunk,all of the fuel cannot be used from the tank.
As soon as any part of the clunk becomes exposed, the engine
will stop due to air entering the fuel pump.
2 Always use a fuel filter. We recommend YS filter ( YS1195 ).
With this filter, you must remove the cloth portion of the filter
and leave both the metal filter screens in place.
START UP
1 Always break the fuel line between the fuel filter and the tank for
filling.This will help to prevent dirt from entering the fuel pump.
To prevent flooding the engine, clamp the fuel line with a hemos-
tat or clip where it enters the fuel pump.
2 Open the high speed needle 2 turns from the closed position.
The engine should run very rich with the recommended fuel and
glow plug. We recommend YS 20/20 fuel ( 20% nitro / 20% oil )
which is available from several manufacturers.
3 An electric starter is mandatory for starting this engine.
Attempting to hand start this engine is difficult and dangerous.
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 maximize 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 containing 15% to 30% nitro, and oil conn-
tent of 20% to 24%. Synthetic oil only. If you use caster oil, no
more than 2% is recommended.
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 with
out the glow driver.
4 After the initial 20 minute break-in, mount the engine in the air-
craft 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 counter-clockwise, the mixture is richer.
A good starting position for the high speed needle valve is 2 turns
open from the fully closed position. At this setting the engine will
be very rich and may die when you remove the glow driver.
If this happens, turn the needle valve in 1/2 turn and try again.
The final running setting for the high speed needle will be approx-
imately 1 to 1-1/2 turns open from fully closed.
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.
REGULATOR ADJUSTING
DO NOT ATTEMPT TO ADJUST THE REGULATOR SCREW WITH
THE ENGINE RUNNING. STOP THE ENGINE BEFORE ADJUST-
ING THIS SCREW
The low speed adjustment is the regulator screw on the front of the
engine. Turning the screw clockwise will richen the idle mixture, and
counter-clockwise will lean the idle mixture. It is preset at the factory
but may require further adjustment depending on fuel and conditions
in your areas.
1 Wait until the engine is up to operating temperature before adjust
ing the idle mixture.
2 Close the throttle gradually to an idle( approximately 2,200 rpm ).
Let it idle for 15 -20 seconds and then slowly advance the hrottle.
The adjustment is correct when low to high speed has a smooth
transition.
OPERATOR’S MANUAL
DZ170
(Parts No. YS0089)
SPECIFICATIONS
Bore
34mm
Stroke
30.8mm
Displacement
27.95cc
Weight
955g
Practical rpm 2,000 -10,000rpm
fig.1
fig.2
fig.3
Fuel Filter
6
25
58
134
114
Regulator
Fuel Tank Clunk
High Speed Needle Valve
PROPELLER INSTALLATION
Due to the high output power of the DZ170 engine, it is supplied with
a double locknut system for added safety. If you use any other type of
spinner or prop nut device, make sure it is of the double nut type.
1 Mount the propeller and tighten the rear nut. Next, tighten the
front nut as shown in fig.2. The rear nut has an 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 7,800 to 8,800 rpm range.
We recommend sizes 17X13 to 18X11. Other prop sizes may
be used as long as the correct rpm range.
Tappet Clearance
