1989 nissan 90 hp... what is the purpose of the oil cap on top of motor?

[Wrecking Crew]

I know the fuel/oil mixture servers as both fuel and oil for motor. What's the purpose of the the oil cap on top? Am I missing something here?

 

[GA_Boater]

Welcome aboard.

It's the filler for the oil reservoir.

You need this - http://www.nissanmarine.com/tech_talk/pdf_files/Nis60C_70C_90A_120A2_140A2.pdf

 

[flyingscott]

Your motor is oil injected no need to mix unless someone took it off.