I have been having a bear of a time getting my os 50 hyper to tune. It run perfect the first two years. last year I could not get it to run right. so I just flew my other aircraft. This year i want to fly my evo 50. the transition is the problem. I can set the low speed nice. the transition and the high speed are the problem. The high side wants to be way lean to even make the transition, then it gets hot and dies...once the engines warms up its a bear to run. I can get about a 1/4 tank of fly time before it starts to act up.

I have gone through the entire fuel system and carb several times to find ANYTHING wrong... I dont see any problems..no dirt or crud..no holes in fuel tubing..(replaced that twice)..my last thought was maybe the carb is leaking air...I dont know, I think I am grasping at straws any more.

If you have ran the engine lean too many times, it might be time for a rebuild. I can't make a more educated suggestion without looking at some pictures as a minimum. </p>

Rafael</p>

You could try using a carb smart system. Are you using the correct glow plug + fuel? Check the muffler fitting for the back pressure line to fuel tank. Is it clogged?

Could the backplate be loose or the backplate "O" ring be damaged. With this condition it could be tuned for a decent low throttle speed, then suck to much air at higher speeds. I've seen this many times.

I found that a #7 os plug did wonders for the operation of the engine... I now have my engine back at full power!  wish I would have thought of it sooner...