|
Table of Contents:
Understanding the fuel system on all YS 4 Cycle engines, FZ53 ~ FZ140. As you know the YS 4 cycle engines work with a pressurized fuel system. This system is what delivers the fuel from the tank to the engine. I will start with the pressure coming from the engine to the tank first. How the engine produces pressure will be another topic. As the engine turns, it will develop pressure. Part of this pressure is fed into the tank via the (return line, or pressure line, or tank overflow line). This is where the check valve is located. The job of the check valve is not to let pressure return back into the engine and keep pressure in the tank. The amount of pressure an engine develops is between 6~9 lbs. at full throttle. Now that we have a tank full of fuel and pressure, we need to control it before it floods out the engine. This is done with the fuel regulator. The regulator is just an open or closed valve that is like a gardening hose sprayer, on or off That’s it. The regulator does not control tank pressure or any air pressure at all. Controlling when the regulator
opens and closes is the next thing. If you take off the regulator assembly, you
will see a cavity in the engine case with two holes "Except for the FZ140". The
center hole is where the pressure comes in from the crankshaft. The hole that
is drilled at an angle is for the pressure going to the tank. As you turn the
crankshaft, you will notice the center hole will open up. This is when the
crankcase pressure will push on the diaphragm. At that moment the plunger will
open and fuel will pass throw the regulator and into the carburetor. As the
crankshaft’s hole passes the opening, this will drop the pressure in the
cavity and the regulator plunger will close stopping fuel from passing to the
carburetor. Propeller Selection The choice of propeller is of great importance. Here I will try to explain in a simple way to choose prop for aerobatic use Over the past 10 years, APC has almost been dominating the aerobatic scene. APC is a very efficient propeller design, especially the tips, which make them very quiet and efficient. We want good static force, used during long vertical climbs, which keeps the model climbing without loosing too much speed. The static force should be greater than the weight of the model. This force is very much dependant on the diameter of the propeller, the largest volume of air as possible should be set into movement by the propeller. One more advantage of using large diameter is that the "rotating disk" acts as an air brake during vertical dives. Speed is needed to make the plane fly, but we are not looking for as high speed as possible. We want a speed fast enough to make the plane fly steady, but not too fast which will make the turn-around program feel and look very stressful. The speed is dependant on the propeller pitch. The maximum engine RPM used during flight is about 8000 - 9000 rpm. With this criteria in mind we can select a good propeller size. At our disposal is the engine power (EP), which will be loaded by the propeller. An increase of propeller diameter (D) will increase the engine load. The greater the propeller pitch (P) will also increase the load of the engine. A simple formula would be like EP = D x P. So we must make a compromise between static force (diameter) and speed (pitch). (Source Data Swedish F3A Web site) Suggested propeller sizes for YS four strokes are as follows: - YS63FZ YS 120 AC YS 120SC YS91FZ YS 140FZ YS140L Most common fuel system problems:
Using in-line fuel filters is a good way to prevent junk from getting into the carb but remember, anything that can go into the carburetor can make it’s way to the fuel regulator. I have seen the following stuck in regulators and inside engines:
Starting Procedure
I have heard, listened, talked about and even shock my head from side to side hearing some of the methods on how to set carburetors on model airplane engines. All I can say is WOW. For the most part, I think some people really don’t know what Pre-detonation is or what it sounds like. Let me tell you that IT IS BAD…….. Detonation is when the piston is coming up on the compression stroke, the fuel will explode and the expanding gases will push down on the piston. This explosion will happen around 42 degrees before top dead center. This means that the fuel is starting to burn before the piston reaches the top. Pre-detonation is when the fuel is starting to burn before 42 degrees or way too soon. This is when the engine will start working against it’s self. If the explosion is too soon, the piston has to work harder to reach the top. The sound you hear is a pinging or rattling type noise usually just before the spinner and prop start to fly off. Yes the YS engines are fuel injected but it is a different story when the engine is at idle. The fuel system changes from injected to sucking the fuel. When you first fire up your engine you always want to run it rich........But after break-in you start to lean out the top end to the max RPM's. Hopefully you are not exceeding 9,000rpm's ????? That is for the 140, 120 and 91. The 53's and 63's like to run at 11,000rpm's. Next you want to bring your engine to an idle. The proper idle is 2,000rpm's. Not 22 or 25 or 3000, set at 2,000. This is when the engine starts to suck the fuel Via vacuum. Above 2,000 it will start to inject the fuel. TOP END After you warm it up and slowly bring the engine up to full throttle, set the top end to it's max rpm's and back off or richen up the needle 3~4 clicks. LOW END After top end is set, bring it to an idle 2,000rpm's. From full throttle set your trim so it will hit 2,000 instantly not drop slowly like 35,30,25,22, 2,000. NO it has to hit 2,000 BANG.........After about 3 seconds, the engine will start to let you know if it is to lean or rich. If the mixture is to rich, the rpm's will start to slow down 2,000 19,18,17. Lean the low end. If the mixture is to lean, the rpm's will start to speed up 2,000 21,22,23. Richen up the low end. Remember, after you adjust the low end, always bring it back to full throttle and back to an idle to test your adjustments. DO NOT CHASE THE MIXTURE. make the adjustment within 5 seconds when you hit idle, Do not let it idle for 10, 20 seconds and try to adjust again. You must bring it to full first and back down to check the adjustment. After adjusting the low end, it should idle at 2,000 consistently for about 20 seconds. After the 20 seconds, bring it back up to full throttle by rolling the throttle stick up. DO NOT NAIL IT TO FULL !!!!!! THROTTLE............ Roll it. It should take you just over 1 second to go from idle to full. Another trick to test if the mixture is correct is to pull off the fuel line at the carburetor at idle. There should not be any fuel coming out of the fuel line. If you do, you are still to rich. This is best done on the bench and not on the plane. With this last test, many other factors can cause fuel to come out of the fuel line at idle.
140 Limited with YS Soft Mount the YS Soft Mount Part number YS0001 for the FZ140L
Well I hope this is of some help. Till next time Rick Mattie  Updated February 28, 2004 |
