air fuel ratio

[paulmars]

air fuel ratio question.

On my oil heater adjusting the air band and shutter I see the flame getting larger and larger as i decrease the air. Set to the smallest air intake the flame is the largest. I never see smoke.

I did a complete tune up last season and noticed this condition, then and again this season.

Your thoughts?

thanks,
paul

[paulmars]

between 0 and 1 on smoke spot test. 475° F flue temp before barometric damper.