Onan 5500 Marquis Altitude Adjustment
I have the same generator and altitude adjustment knob. The only time Iíve adjusted it has been a few times the generator has been surging and not running smooth and Iíve changed the altitude setting just a bit and it corrected the condition and ran smooth. To adjust all you do is turn the black knob on the bottom. Thereís an indicator on the side of the knob. Itís not an exact measurement, but itíll get you in the ballpark. Iíd say donít touch a thing if your generator runs fine, but if itís not running quite right adjusting the altitude knob may correct the problem.
Kirk - "Fly Navy"
98 Fleetwood Pace Arrow Vission
Itís not old - Itís Vintage