Born2Fly

My Feedback: (21)

Hi,

I need you help because I am confused with the engine setup I have. I bought used DP Ulitmate equipped with O.S. FS-120S engine. I think it has a Slimline Pitts muffler on it. The fuel system setup; is the fuel dot and the tee on the fuel line, the ventilation is just the line on the bottom of the cowl (it is not connected to the muffler pressure tap). The engine I have does not has a pump, so how the fuel going to go to carburetor???? Also am I going to flood the engine during fuelling? How I can use the chock valve, and in general what is this thing is for? Those questions might be simple, but I could not find any explanation in the manual. Please help.
Thank you in advance.

Bax

My Feedback: (11)

With your O.S. FS-120 Surpass w/o pump, you basically plumb the fuel system like any other engine, four or two-stroke.

The fuel line from the clunk in the tank goes to the carburetor. A pressure line goes from the muffler to the vent in the tank. This should go to a top-forward location in the tank.

If a third line for fueling is used, it should dump in the bottom-forward location in the tank. You'd then cap this line with a fuel dot or similar.

Do not use a check valve anywhere in the fuel system. It's not needed. If you plumb the system properly, you need no "tee" or anything similar.

Born2Fly

My Feedback: (21)

Thanks. But first, I have to use the tee to put the fuel inside the tank.I do not have a third line for the fueling and I do not have access to the engine/fuel line and I do not have the ability to disconnect the fuel line from the carburetor because of the cowl. Will I flood the engine with this setup? Second, I read in the manual and on the page 3 (bottom, left) it says that you can use pressurized and non-pressurize systems? Could you please explain what non-pressurized system means? (I am not talking about the engine with the pump; I read this in the manual for non-pumped OS 120S-E) Also I really want to know what is the choke valve is for? Thank you for your help.

Dr R H Malik

The setup explained by BAX is simple and fool poof. However if its not possible to plumb a 3rd line from the tank (for fueling/defueling) then use a Du Bro fueler. Using a T will flood your carb.
regards
riz

Bax

My Feedback: (11)

If you can't use a 3rd line for fueling, add a fueler fitting to the fuel line. This will prevent fuel from flowing towards the carb when fueling.

A non-pressurized system means that you're not using muffler pressure to the tank. The tank is just vented to the atmosphere, and the engine draws fuel from carburetor suction.

Born2Fly

My Feedback: (21)

Thanks, Bax. That is the system I have here. Is it ok to use non-pressurized system for 3D? Will the engine get enough fuel on the high Gs? Thanks

Bax

My Feedback: (11)

There's no way to know if the fuel system's "right" until you fly. Generally, the standard setup is fine for almost all types of flying, but some specialized types may not find it suitable. 3D flying, with its emphasis on low-speed, high-alpha maneuvers may cause a problem with cooling, fuel draw, and so on. You won't know until you fly and see what happens.

Born2Fly

My Feedback: (21)

Thanks, I was personally thinking that the pressurized system is more suitable for 3D flying. I understand it hard to say what will happen, but on another hand I do not want to risk $1200 plane and figure out that my engine does not work good without the pressure. Will the fuel consumption is better with the pressurized system??? Thank you.

Bax

My Feedback: (11)

There's really no difference in fuel consumption whether you use muffler pressure or not. If the engine's turning the same RPM, it will use the same amount of fuel. The main difference is that when the fuel system has muffler pressure, the high-speed needle will be slightly leaner than when straight suction is used.