This engine runs rich at low to mid throttle openings. Low speed needle is already leaned out as far as possible before lean stumble. I'm trying to avoid leaning out the high speed needle as I already have it set near peak. I'm stumped!

Any ideas or sugestions please pass them along.

Hi there,

What glow plug are you using?
A friend of mine has had almost the same symptoms with his Evo and was told by one of the shop owners to only use the Evo glow plugs with the Evo motors. Apparently they have a longer reach than the other brand plugs. At the time of his troubles he was using a O.S 8 plug. The motor is now sorted and is running as good as ever before, after changing to the Evo plugs.

Best of luck.

This is the gas forum.
he needs tu tune the carb. Lean out the low needle bye and bye, whilst (IMPORTANT!!) opening the high needle as needed for best power. When transition starts to suffer, the low is too lean, so go back to the previous setting.

Thanks Pe, I'll give that a try.
I have a couple of questions for you, if you don't mind:
1.) At what degree, or point, of throttle opening does the high speed circuit of this type of carburator start to play a significant roll?
2.) I have found that leaning the low speed needle, with aircraft static on the ground, to the point of lean stumble does not necessarily equate to lean stumble ocurring when airborne. Does this sound correct to you?