YS Engine Setup
Posted in May 21st, 2008
Tuning the YS 4 stroke pressure system engines.
These engines are not Pumped as some believe. Rather the engines send crankcase pressures back to the fuel tank. With the use of a check valve in this pressure line the tank maintains its pressure. Under pressure the fuel in the tank is forced to the engine. The regulator is nothing more than the door man of the system. When the pressure in the case gets to a certain level that exceeds the pressure created by a small regulator adjustment screw and spring tension on the plunger it will open up allowing the fuel that is already under pressure in the tank to flow freely. This is the door man reference, when the pressure on the diaphragm pushes on the plunger it tells the door man to open up and let the fuel come through. The system is as simple as this. Because the engine is force fed fuel it does not suffer from problems with tank location (within reason), and upright or Inverted installations do not matter. The engine does not know the difference. If the engine runs fine while upright yet flipping it inverted it wants to load up. The mixture was too rich to begin with. This is the only affect inverted installs will show different than upright.
The problem is there are several possible problems or pitfalls with this system. Dirt and dirty fuel is the number one. If a chunk of dirt or debris gets in the way the door can’t close. If the adjustment screw is not putting enough spring tension on the door it will open sooner and stay open too long.
The symptoms of this are dripping fuel from the carb while at idle rpm. So you have two possible problems regulator too rich and not closing soon enough or dirt and debris in the regulator keeping it from closing.
PROP SIZE RECOMMENDATIONS:
YS 53/63 — 11 x 7, 11 x 8, 12 x 6, 12 x 7, 13 x 5, 14 x 4.
YS 91/110 — 13 x 12, 14 x 10, 14 x 12, 15 x 8, 15 x10, 16 x 6.
YS 120’s – 15 x 8, 15 x 10, 15 x 11, 15 x 12, 16 x 8, 16 x 10
YS 140 FZ, 140L, and 140 Sport - 15 x 13, 16 x10, 16 x 11, 16 x 12, 17 x 8, 17 x 10.
These above are just general in the range prop choices. You will need to run a prop and fuel that gives the target rpm numbers from the list below. These are the rpm numbers where the engines are best in performance and loads.
YS 53/63 — 10,500 to 11,500
YS 91/110 — 8,800 to 9,800
YS 120 – 8,200 to 9,200
YS 140 – 8,000 to 9,000
YS 160 – 7,800 to 8,400
YS 170 – 7,800 to 8,400
Now various versions of these engines will be more powerful than others. You may need to change props based on which versions you have.
In order from the lowest power output to highest. These ratings are a little subjective but get the idea. A worn out engine that is higher on the list might be the same or weaker than a lower rated engine. This guide is simply a general guideline when the engines are performing at their peak.
53FZ
63FZ
63FZ-S
91AC
91FZ
110FZ
110FZ-S, 120SF, 120NC
120FZ
120AC
120SC
140FZ
140FZ –Sport (140 Sport)
140FZ-Limited (140L)
140DZ
160DZ
170DZ
Down and dirty this is how to set YS Pressurized engines. This does not apply to the DZ or Direct Injection Dingo engines.
Follow the prop chart above. OS #F or YS #4 Plug.
Fuel Cool Power 30% Heli fuel. You can choose your own, but make sure it has at least 20% oil content, and is 100% synthetic oil. I feel that many problems with getting the engines to operate properly is poor choices in fuel. So run the Cool Power and you don’t have to worry about it.Start it warm it up slowly…about 4000rpm for a say 30secs to a minute.
Then throttle it up Using a Tach set the Peak rpm and back it off about 200-300rpm. One click at a time waiting a few seconds for the change to take affect. The fuel has a long way to go before your change will take affect.
Next go to 4000rpm with your tach. This will be a 1/4 throttle position or about. Hit 4000 rpm and watch the tach. Surging up and down is lean. Loading up and slowing down over time at the 4000rpm is rich. Watch it for about 30-45secs….and see if its lean or rich. The regulator screw works the same as a HS needle valve. IN or CW is Lean. OUT or CCW is rich. Any changes you make to the regulator will affect the other settings so re-set them. Do the HS again and then check the midrange or regulator adjustment again. 1/8th turns are good here. Normally the regulator is not really super sensitive unless its really far off. Starting locations for the engines is flush with the case housing on the YS engines. The newer style external regulators on the 110S and 63S are slightly different. The system works the same way but the default start point is usually slight in from flush with the case.
I need to make a special note here…the regulator is factory set. It should be close and only need a slight tweak one way or another on very few engines. 90% of the engines out of the box the regulator is correct. Often guys start messing with the regulator and it will affect both the top end and idle mixtures….There is a time to adjust the regulator, but usually these adjustments are for minor tweaking. The instruction here tell you how to set it properly. If you find you are making major adjustments to the regulator something is wrong.
I do not subscribe to the theory that the regulator is perfect don’t touch it.
However I will say that most engine problems with YS engines are operator induced and start with not understanding what the regulator does and how it affects things. The instructions I give here are to explain it and tell you how to make a change if it is needed. As the engine breaks in the HS needle will change, perhaps the air bleed low end will change too, but the regulator should not need any adjustment. Its just not that critical until you start turning it a bunch off its setpoint.
Another NOTE: NEVER bottom out the regulator screw. NEVER and I will repeat NEVER screw the regulator screw all the way in to count the turns open. The regulator screw has a small spring on the backside of the screw. This spring puts pressure on a small silicone stopper, similar to a toilet stopper. If you bottom out the regulator screw it can damage the silicone stopper. The reference that you need to use on the regulator screw is relative to flush with the regualtor housing.
Idle mixture is fine tuned by the air bleed screw in the throttle barrel. The rpm where you set this mixture adjustment is at 2000rpm. This screw does nothing above about 2200 rpm…and its all regulator above that. So the same test surging up and down or dropping to a high reving idle then cutting to the low 2000rpm is also lean. Hitting a 2000rpm solid then loading up and slowing down is rich. Now since this is an air bleed screw and not a Needle valve it controls air flow. More air (Opening it) will lean the mixture and Less air (Closing it) will richen….So CW is rich and CCW is Lean. This air bleed screw is backwards the direction of the HS needle and Regulator settings.
Now once you get this all set this way its really close. If you get a slight detonation on throttle up…and the engine is warm and up to temp…then richen the regulator screw just a little…maybe 1/8th or less.
OK one more word of warning. Don’t run the engine for long periods of time on the ground unless it is at low 4000rpm and below. It will get hot quickly and any changes you make will not be correct when it’s too hot. My rule of thumb is get it close and then let it completely cool off then check the mixture again…Fine tuning it all along.
When the engine is cold and the tank pressure is not up to the proper number it will act a little lean on a thrown open throttle. The pressure in the tank is what delivers fuel. The engine SUCKS zero fuel unless it is at 2000rpm. Above 2000rpm the engine relies on the fuel to be pushed through the pressure regulator to feed it. So if you throttle it up too fast and the pressure is not built up it will detonate and go lean on you…
A single needle setting is not magic and works for all the engines…it will vary a bunch with conditions. Fuel choice will play a role. The less nitro the leaner the mixture will need to be. The lower your elevation and ambient temps the Richer the mixture will need to be
Troy Newman
Team YS