Guys i would need some help for a friend of mine who owns a 3 year old Saito 50.

Well this is what happenes....It starts up with full rpm but as time passes it loses power/rmp. after a few minutes the max rpm is so low it cant even pull up a 20 sized aircraft. we have tried tuning and all but still no improvement(cant be the tuning as the engine has good rmp when the engine is just started)
But the engine does not cut off but still runs with very little rpm(like its idling at open throttle)

SO what can be the problem? And what should be done.
Thanks for the replies and help guys.

Some additional information would help, like what plane is it mounted in, is it enclosed in a cowl, and/or it's mounting position.

Initially it sounds as if it might be overheating...

Mike

Sorry for not including those details....

Well it used to be on a Kyosho Tiger Moth(40 size) and was enclosed under a cowl......It was mounted inverted.It use to fly well since it was brand new till a few months back when it started its present problem.

Hope you guys can help out here.
Cheers.

The engine is definintely getting HOT.

First, you need adequate cooling airflow over the engine, or it will overheat no matter how the needle is set. The key to cooling airflow is to open up the area BEHIND the engine, to allow the hot air to get out. You need at least twice as much exit area as entry area for cooling air. The air expands as it's heated. Try flying with the cowl removed.

If having the cowl removed doesn't help, you're too lean, period. You're trying to compensate for the inverted engine by closing the main needle valve too much. Instead, adjust the low speed needle valve for a smooth idle, and open the main needle valve somewhat. You may need to resort to onboard glow or a fuel regulator because the carburetor is lower than the fuel tank. Try to lower the tank in relation to the needle valve if you can.

THanks Matt but any other ideas......
as it was flying well on that plane for over 2-3 years and why is it suddenly having this problem... what i mean is that it was always mounted inverted and was enclosed under a cowl(the cowl has enough area for it to breath as well i think) and why is it only now getting over heated??

Thanks for the help.

It sounds like the exhaust valve may have carboned up. If you feel comfortable, try removing the ex valve and scrape the excess carbon away. You don't need to get rid of all the discoloration, just eliminate the black caked on stuff.

Good luck!

Also run a pipe cleaner through the pressure nipple on the muffler.