Hi Jim,
I am guessing this is a Moki 1.8, it doesn't sound like it is broken in yet they seem to take quite a while.
I am running Bryons 5% with a 20*8 schimitar and it turns right at 6800 and seems happy enough.
since speed is not an issue with this plane I was thinking of a 20*6( think Zinger makes one), lots of static thrust.
Set the low speed where ever it needs to be to run right. mine is between 2&3 notches lean.

If it is not to much trouble let me know where you have it balanced, just looking at the wing I would think
the cg needs to be further back than the 1/2 in. from the spar that the plans call for.

Mike,

Bringing this thread back to life:

Has anyone had their Extra snap in half right in front of the leading edge.
Have had two club members have this happen to this summer.
They now have the planes back in the air with mods to the front.
From motor mount back and going around the LE with 1/8" ply for stronger support

Anyone else with this problem?

One is powered with a MOKI 2.10 and other is MDS 2.18 with Perry Pump (mean motor with this pump on)

I haven't seen that happen, but that does seem to be the weak spot at low throttle my 1.8 shakes back and forth about an inch.
and all of the motion stops at the leading edge. So how did they mod it to make it stronger ???

Mike,

PS: this is the best torque rolling plane I have ever flown. It just hangs there and turns!!

Yep.it happened to me,I made the same mod that your friend did. There is no ply at all in the plane,all balsa. I can't understand the gas engines on these planes,they are simply not built for it. Especially when a $250.00 1.60 performs so well on this plane.
Mike