I have both the 180 and the 210. My motors are cowled and a lot of my flying is during the summer. Here in Louisiana the summer is always in the high 90's and the humidity is 150%.
I use the Cline regulator for the Moki motors.

This past weekend a friend was helping me with a test flight of a new airplane. I ran the motor up and asked him to hold the plane pointed straight up, straight down, and side to side.

After the test he commented that something was wrong.
What? I asked.
He said it didn't pick up rpm's when it was pointed straight up. Well no! Thats what the regulator is for. Constant fuel flow at all angles.

In your case your motor is probably going a little lean when you fly at an up angle.

I want you to know that I am NOT a MOTOR EXPERT. This is just my opinion.

Hope this helps.
tonyc