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YS four-strokes general information                                                                                     Basic aticles by Rick Mattie

 1. Recommended fuel

a)

15 to 20% nitro and 20% oil by volume.

b)

use 100% synthetic, but 18% synthetic and 2% castor is also a good mix.

c)

YS 20/20 Power master or THE's 700R, FH-20,FH-25   

 

 2. Initial settings

a) 

Low end needle 2.5 turns out from full in (91 and SC only)

b)

Regulator flush

c)

High end needle 1.5 turns out.

 

 3. Fuel tank

a)

Watch for leaks, especially ones that only appear under full pressure. This can cause surging.

b)

replacement every 150 flights.

 

 4. 

Surging Could be worn out piston. Piston life is about 200 flights.

 

 5.

Regulator tab goes forward.

 

6.

Always replace all gaskets upon re-assembly. Possible exception to this rule: valve cover.

 

 7. 

Regulator edge may cut diaphragm. Knock the edge off this or return Futaba in U.S.A

or Yamada in Japan.

 

8.

Replace head gasket if burn ring visible. Okay to keep if clean.

 

9.

Cleaning. Use soap and water or methanol. DO NOT USE GASOLINE! Ultrasonic cleaning  recommended.

 

10.

C-clips wear excessively if not adjusted correctly. Replace every 150 flights. When adjusting valves

it is best to adjust on the  tight side.

 

11.

Never use petroleum-based after-run oil. Klotz okay.

 

12.

Plugs. Use OS F only.

 

YS 91

 1. Initial settings

a)

Low end needle 2.5 turns out from full in

b)

Regulator flush

c)

High end needle 1.5 turns out. Note that this engine richen slightly after it warms up. Do not re-  peak

when  this happens   as  it will begin to lean as it heats further.

 2.Recommended RPM : 9200 max.

 3.Loss of power when heats up : may be loose liner- send back to Yamada in Japan or Futaba in U.S.A..

 4.Can't shut off or can't set top end needle

a)

Look for vacuum leak in valve cover. Could be gasket or ground off head.

 5.Loss of power

a)

Ring

b)

Rear bearing : Should be replaced every 150 flights.

 6.Recommended prop : 14x10  (13x11,13.5x10~13 propeller are not bad, too)

 

--------------------------------------- New FZ 140L(Limited) engine ------------------------------------

 

* The YS140 has no timing marks.

  * Note that the fuel injection system only injects fuel at speeds exceeding 2000 RPM.

     Below this, fuel is inducted in the normal manner. This is valuable information for troubleshooting!

  

  * Small bubbles in the regulator line are normal at idle and typically go away at higher throttle settings.

     Bigger bubbles are symptomatic of diaphragm or regulator gasket problems.

 

YS 140

1.

Availability : due out at the end of the year for about the same price as the SC. It is 10gm. lighter than

the SC and shares  many  parts.

2.

Prop. : try 16.5x13.5. Don't over-nitro!

 

Setting up a YS 140

1.

Always set up the top end first and see that it runs consistently there.

2.

Go to a 2000 RPM idle. If the RPM slowly goes down, then the low end needle is set rich.

3.

Set the low end needle so that there is about a two second delay in transition to full throttle

due to richness. Engine should  not  immediately bang to top end.

4.

Set the Regulator at 3000-4000 RPM. If speed slowly drops in this range

then the regulator is rich and needs to be leaned.

 

Breaking in the YS 140

1.

about 10 ounces of fuel through the engine and then puts it into the plane. Use a prop that maybe runs in

the 8200 to 8300 range.

2.

Note that the low end needle is an air bleed type and its action has limited after about 4 & 1/2 turns out.

3.

Note that the rotor screw is a backward thread. Upon reassembly, use a dab of green Locktite on it.

It's okay to bottom this  screw out.

4.

YS claims that the rear nipple in the 140 back plate is a bleed that helps keep the regulator open longer

than the connection  used in previous engines.

5.

Conrods are not symmetrical.

6.

The hole for the crank pin has a wider taper on the crankshaft side.