2002 225 ox66 surging

I have a 2002 225 ox66. Most of my time is spent *****ing between 1600 and 1800 rpm's. When I try to bump it up above 1800 the rpm's will fluctuate between 1900 and 2400 and will not hold steady. The rpm's will hold steady once I get the throttle to about 2400 and above. Any ideas on what is causing this and how to remedy?

[Aleutianwest]

With all that *****ing the O2 sensor is probly plugged up and needs to be cleaned and check the tube in block