I agree with the other responders an all counts. The park is NOT the proper place to fly a nitro powered plane. Even if space permits, you have no control of others walking into harms way. As for the engine, it definitely sounds like you're running too lean. I assume you have a 2-stroke. Lots of oil on the plane is a price you have to pay. You should have a "cloud" coming out of the exhaust at full throttle. To set the high speed needle correctly, bring the throttle to full and slowly turn the high speed needle clockwise until you reach the maximum rpm's. Then turn the needle back (counterclockwise) at least three "clicks". To test for the proper setting, pinch the fuel line closed. If the engine gains rpms before stalling, it is correct. If it loses rpms or quits suddenly without gaining speed, it is too lean. Richen the mixture slightly. Next, bring the throttle to idle and wait for the engine speed to settle. Then advance the throttle quickly. The engine should increase rpms smoothly, If it "spits and sputters" it is too rich. Hope this helps.
Please find a safe place to fly, and consider finding an instructor to help you.