Gas diluting engine oil

I have a new T25 high thrust Yamaha kicker.
I have been using regular grade marine gas. I have noticed that the engine oil shows higher on the dipstick over time, and a friend tells me it is because of incomplete combustion caused by burning low octane fuel, which he says causes the fuel to dilute the engine oil. He suggested I switch to premium gas. I run the kicker off the 100 gal tank on my boat, which I fill with regular marine gas at the dock (all that is available).
Should I be running my kicker with a portable tank filled with premium?
Thanks for any thoughts on this.

Make sure thermostat is in place and working ------------------check fuel pump for a leak------------------Make sure float valve in carburetor is working and not leaking.

only 5 things cause this

bad t-stat
bad fuel pump
valves not adjusted right
under-propped
or your trolling all day long and not running it hard at the end pf the day

Thanks for the help.
When you say underproped, are you saying the pitch isn't great enough, meaning it could be running at too high rpm's?
I am using the 9" prop that came stock with the motor.
Do you think I should try an 11"?
If that isn't the fix, I'll take it in for servicing......hopefully covered by warranty.

to low of RPM's when at WOT

so as JIT said, to large of pitch, instead of 11 a 7 to raise the rpm, but i would be looking at the other items first, personally i would be looking at the pump diaphragm.

Thanks. Will check out both possibilities.