hello,

i have a problem with my os 200 pump. On the ground, everything seems ok : 8000 rpm
with an apc 18*8. In flights, sometime i have the power and sometime not, and after few minutes, my engine stop...so, what's my problem with that engine ? how can i set it ?

thank's

stephane

Stephane,
I think you have an air pressure problem in flight, the pump regulator and carb intake must have the same atmospheric pressure. If your carb inlet or regulator inlet in the slipstream or receiving ram air and the other is not then an imbalance will occur and will drive you nuts. Try using an extension tube or placing a cowl in front of slipstream airflow and your problem should be solved.

Ciao,
Jerry

If your engine will run perfectly-well when it's on the ground or on a test stand, then there's nothing at all wrong with it. Something would then be wrong in the engine/airframe/fuel system combination. Many times, in the air, the airframe can vibrate enough to cause the fuel to agitate in the tank, which will add air to the fuel and lean the mixture. That is quite common. Also, cooling may be a problem once the airplane starts flying, and you get overheating.

You will have to check things very carefully.

Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.

One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.

To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.

At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.

With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.

Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.

thank you bax,

i have lean the engine like you said, but how can i set idle mixture ? today, 3 flights, and same problems...on ground, after few seconds, my idle varies. Could it be a problem with pump or regulator ? how can i know that ? is it possible to verify myself pump or regulator ?

thank you