Ercoupe project flies unstable in pitch and yaw

5 degrees down is almost twice the correct 3.5 degrees

www.ercoupe.info/uploads/Main/drawings/a-654.jpg

I'm pretty sure I am reading this drawing correctly, 3-1/2 to the right, 5 down. That raises an interesting conundrum; which is correct?

where did you find that drawing? I looked on ercoupe info and could not find it. The drawing that I am referring to is in the maintenance manual and clearly says 3-1/2 degrees down and 5 degrees right. The trim tab has been inspected.

According to Assembly Drawing 415-31913, down thrust is 5 degrees down from the airframe centerline. That may be within your margin of error, depending on how the angle was measured. And it doesn't include compressed lower engine mount rubber bushings which would increase the engine angle.

A tail too low can cause the plane to take off before you tell it to. The top of the vert stab should be about 75" above the level ground when static.

A mis-adjusted or seized trim tab can cause a surprisingly high AOA on departure which looks/feels like jumping into the air.

These are two things that are easy to check, that I haven't seen anyone mention yet.

The Ercoupe, by design, is almost impossible to get out of CG. all the seats and fuel tanks are in a straight line across the plane, your only way to move it aft is baggage.
You didn't leave your A&P in the tail cone did you?

Checked thrust line today and found that I have 6.5 degrees of down thrust! I don't understand why too much down thrust would cause the plane to want to jump off of the runway, but could see why it might be touchy in pitch.
We are checking the weight and balance this weekend to rule out an aft cg before doing anything with the engine mount.
If any of you can explain why too much down thrust would make the airplane want to pitch up, I am very interested as it seems counter intuitive.Any other suggestions appreciated.