I have an 03 F90.its pretty easy.drain plug in rubber boot on back of upper case. I hang a bucket on the back of the motor w cowl off to catch the oil.might need a filter wrench,I did.I believe you can view the owners manuals @ yamaha outboards website for your year motor,im not sure they are the same.
I got it used in 07,on a g3 1860sc jon boat.i like it alot. its quiet.kinda important as i can put my palm on the motor when im steering its right behind me!and You can barely hear it at idle from the bow.it starts instantly when im fishin.takes a few trys when it sits for 2/3 weeks.i had some issues before installing a water/fuel filter.03 f90 has 4 carbs.the new ones are fuel injected?It runs strong w a new alum 4 bld.it is a heavy 90 horse 370lbs.but i dont think thats an issue on fiberglass boats.my boat wieghs bout1600 when loadd.and it will jump on plane w the shallow v.I havnot seen any bad posts about them.
Great motors... basically the F80, F90 and F100 are the same, all 97 cubic inch four cylinder DOHC EFI four strokes. Yamaha have a great reputation here in Australia (although we don't get the F90, only the 80 and 100) and are the country's biggest selling OB manufacturer despite their products being more expensive than their competitors. We're a cynical lot, and unless it's good, we won't buy it. Yamaha also have a good dealer network and good spares supply as well as four year private use warranties on their four strokes. I'm not attached in any capacity to Yamaha, yet I don't hesitate to recommend Yamaha four stroke outboards - I'm on my second - and I know what brand I'll be sticking with for number three:~
