Lost velocity when going from CO2 to AIR ?

[spyderon]

I am new to markers and picked up a very barely used MR1 which I used twice on CO2 and was Chrono'd to approx. 280 both times. When I returned to play for the third time, I cam with a new 3000 psi aluminum tank and I got chrono'd at just under 200. What gives?? Could it be the marker breaking in because it was hardly used, or something worse? I toy'd around with the velocity adjuster at home but didn't have a chrono. Visually it didn't seem to much different with the spring adjusted all the way in or out.

Any suggestions would be appreciated

Ron