I don't understand.
What exactly in that picture do you think might be a problem ?
And at what speed does it choke at 2500 RPM ?
My first guess is that you are lugging the engine; that is trying to make it "pull" at too low a speed for that gear.
2500 isn't much above idle. The only time my engine is turning that slow is in 1st gear just coming off the line.......and most of the time not even then.