OX66 Power Reduction in 1 Motor

I have 2 OX66 250's that are 10 years old and in great shape and well maintained. However, recently one of motors would automatically reduce power once it got between 3000-4000 RPM. Both throttle's were even and then the issues began. It would run at 4200 and then decrease down to 3800,3500, and then 3000 without touching the throttle???

I have run two tanks of gas with ring free as my tech told me it might be the O2 sensor but he was not certain.

Has anyone see this issue before?

Thanks in advance.

Stan in Tampa

[jb123]

run on an auxillary tank to see if its fuel restriction to that side

you can test or swap o2 sensors

have you ever cleaned vst tank filter?

have you ever replaced LP fuel pumps ?

ever changed out fuel filter on motor ?

changed plugs recently?

keep up on your maintenance or keep the mechanics number handy.

[jb123]

if it IS the lp pumps you will see fuel out of the prop. unhook both pump bolts, leave hoses intact and pump ball....if gas pours out then diaphrams are bad.