Most of the people I know who have problems with generators - whole house and portable - don't service them properly...
They basically install them and forget them or store them and forget them...
Mine cycles every Saturday morning at 11:00 am and runs for 10 minutes
When I had a 8000w portable with a generlink cable - I always cranked and ran it for about 10 minutes each month and changed the fluid in it annually like I do the zero turn mower