I have the same motor, same year, had the same problem last year (and same lack of preventive maintenance up until last year). I'd lose RPM's at or above 4200, though it would reach and hold 4200 for a minute or two. Learned everything from these guys on here, you can do it, I did. You will gain a tremendous amount of confidence the more you work on it. Everyone here can and will help you out. You should start with the 3 low press fuel pumps, change them out with new one's. Take the O2 sensor off and clean it AND the exhaust tube. Lastly, change or clean the VST filter.
The exhaust tube (according to Yam) has been redesigned to cut down on clogging, the VST filter has also obviously been redesigned to filter more (I have a photo of the new one I put on mine). The motor hasn't ran this good since new. I recommend picking up the service manual, I have 2, one from Clymer, one from Yam and I like the Clymer better since it has photos as well as step by step instructions.
I think if you do the maintenace mentioned here, you will be presently surprised (and save a TON of $$$$$$).
If you need help, votes of confidence, I and others here will be happy to help. Lastly, if you have access to a fax machine, I could probably photo copy the pages you'd need in the manual and fax them to you. TomS and Megabyte helped me enormously as they have the same or very similar models.
Tim
