Okay, I have the Century Hawk with an O.S. engine with less than 20 flights. When I first start to fly the heli everything seems to be fine but after a while the engine seems to loose power and I have to increase the throttle to keep it hovering and then eventually i cuts completely off.

Hi,
As the engine runs it begins to bed in and turn over freely. This effects the rpm's and therefore mixture.
As the flight proceeds the engine heats up and you loose power.
You will need to re-tune the engine. If you look on the engine fourm you will find really good info as to the method to use.

Hope this helps,

Sounds like your needles are set too lean. Richen them up and then adjust your throttle curve to open the barrel more at the 1/4, 1/2 and 3/4 points on the curve.

Note that the idle screw is important in the hover, it usually needs to be opened for a richer setting then from factory settings.

What OS engine?

you may not be able to make your motor ever run right again as you might have run it to lean and scored the piston or sleeve try to rich'en it up at 2 1/2 turns and run it for a few seconds then lean it a click or two at a time until it is running good but if you start to see it die then land quickly and rich'en it up 2 to 3 clicks if it wont build power or just bogs out then you'll probably need to head to your local hobby shop for a new one.. Oh also change your glow plug sometimes that will cause a strange problem too

hope this helps

i also got a same problem...