I just serviced our 7.5 Onan QD and the spark arrestor was between the two mufflers up inside the cabinet. Not sure if this helps or not but I had to unscrew that as part of the service and then start the generator - boy did the carbon fly then.
Rick and Larrie Dee
1997 40' Newmar London Aire DP CTA 8.3 (Mechanical) 325 Spartan MM
Bringing her back to her glory.
'08 Jeep GC Overland.