On the Dingo just like all the other YS engines. A rich setting will maintain an RPM for a few moments say 2000-2300 and then start to fall off slowly. Another sign of being rich on the pump is dead sticks at idle or after a long idle and throttle up the engine quits. This is usually rich. Could be rich on the Pump and or rich on the HS. The pump and the HS are related and I’ll explain it below.

The Pump too lean will detonate or surge in the midrange. A throttle up and backfire in the mid range is too lean. I set the idle down low ( 2000-2200) and watch the rpms. If they surge up and up down about 200-400rpm this is too lean and you need to richen it. I tend to set the pump lean as I can get without detonation in the throttle up or surging at idle.

The Pump on the Dingo can be thought to control the pressure of the fuel. Again what it is really doing is playing with the bypass loop or kickback loop on the fuel.

The pump basically supplies the same volume of fuel every time it cycles. There is a bypass loop or I have heard it called a kickback line. This bypass line is internal in the pumps body and has a couple of check valves or really they are like a "Pop Off" valve in Boiler system. This Bypass goes from the outlet of the pump back to the inlet of the pump. Basically if it was Electricity it would be a short circuit. The pump adjustment screw controls the pressure inside this bypass line. Again its running off the pressure differences inside the engine similar to the demand regulator on the pressurized engines but this time its allowing the fuel to bypass the needle valve and injector line and short circuit back tot he inlet of the pump. This keeps the pump happy. He is in there just pushing fuel. Pushing the same little drip of fuel each time he cycles. Some is being bypassed back to the inlet and some goes to the big boom. Think of Electricity the bypass line has a resistor in it the adjustment screw is adjusting the restriction. The higher the restriction the more that goes to the BOOM and the low the restriction the more fuel that goes back to the front of the line and gets pushed by the pump again. The more restriction in this line the higher the pressure on the pump outlet side needs to be to push fuel through this bypass line. So when you tighten the screw CW rotation, you are putting more force on the spring which is putting more force on the diaphragm. The diaphragm controls two little check valve or pop off valves. If the pressure in the outlet of the pump is big then the pop off valve opens and allows the fuel to bypass. If the pressure is lower in the outlet of the pump the pop off valve stays closed until the pressure is higher.

The pressure in the outlet of the pump is changing every time the intake valve on the engine opens. The pump can be thought of as a piston that is always pushing the same volume of fuel. The spring tension on the diaphragm tells the pop off valves when to open and when to close. So if you turn the pump in to apply more pressure on the spring then the "pop" off will happen at a higher pressure in the pump outlet line and close sooner. This means more fuel in the injector line and less in the Bypass line. In plain old NASCAR American redneck talk, she gets a bigger gulp of fuel to the engine when less is being bypassed. This also means on the other side that less of the fuel is going through the bypass or kickback line.

A lean situation means that the pop off valves are opening sooner and staying open longer allowing the bypass to happen. So in relation more fuel is bypassing and the engine is getting less fuel to combust.

The High Speed needle valve controls how big the hole is the fuel is being metered through. So it is also affecting the pressure in the pump outlet line. This is why on the DZ motors the HS needle and the pump pressure affect each other. Really the screw is adjusting the bypass line and the HS is adjusting the size of the opening the pump is pushing through. A richer setting on the pump means the hole could be small but I'm going to get as much in there as I can for as long as I can. This means that you can set the HS needle and get the engine to run great at high speed even if the pump is way off. Example you have a really rich pump. So your HS needle is closed way down like 1/2 turn open. For High RPMs the fuel to air is getting mixture at the right ratio and all is good but slow the engine down and the high pressure in the pump outlet is pushing just way too much fuel for the idle rpm and the heat generated at idle and the engine goes cold and the fire is killed.

Now let us take a big step backward. Setting of the motor. We are talking about raw fuel. Not fuel air mixture like in a 140FZ sport or any of the other YS pressure system motors. So when you re dumping raw fuel on the piston and there is too much of it the first thing that happens is the temps go down right? Richer means cooling down. However the principles that make our engine operate are similar to that of a Diesel. Temp and pressure with a little catalyst from the glow plug. So if the temp goes down now things are not operating right and you are putting out the fire. So what happens is at full power all is fine because it has lots of heat being generated, and the extra fuel is burning. But when slowing the engine down now the heat is much much more critical. The engine needs that heat to make its big boom. But you are at idle not making the heat and the extra fuel is slowly smothering the fire. So after a long idle and you throttle up quickly is like smothering the fire. As the RPMS increase the fuel gets there almost instantly and the temps don't come up as fast so the fire just washes away.


By the way this is one reason the YS engines have such great throttle response and transition. The two systems the Dingo and the Pressure system always have plenty of fuel there and ready to burn when the throttle body asks for it. On the pressure system its being force fed by the tank pressure. Anyone pulling the pressure line and seeing fuel squirt 10ft across the flight line has seen this. But the DZ does something similar in the positive displacement pump and the bypass loop.

If you think about the pump on the Dingo you will now see why we use the foam fuel clunks with them. Fuel is a liquid and is pretty non-compressible. So the pump outlet pressure is constant up and down as long as the fuel flow is steady with no air bubbles. Now Air on the other hand is a compressible fluid. A little bubble in the fuel line and the pressure ration for the bypass loop and the injector line are all messed up. This makes the pump still pushes the same volume but now less of this volume is fuel and that makes the engine not gets proper drink of the good stuff. It goes lean if only for a split second. Now lean means more heat, and heat means again pressure changes. So it becomes a never ending battle to maintain the right heat to make the boom and not get too much.


So if you made it through this thesis and you understand I did a good job. If I confused you even more then add glow igniter, and flip prop. Turn the HS needle in to make lots of heat and out to reduce the amount of heat being made. Enjoy!

Troy Newman
Team YS Perfomance