I also own a 1984 gpz900, I experience the same problem. I have tried all that as well. The best things I have found to deal with the problem is keeping it in tune. You would be suprised the difference this can make. Also run a by-pass switch for the cooling fan, and turn it on as it starts to heat up(as soon as you see the needle move above normal temp) This has worked for me. I do alot of slow riding through traffic. Hope this is of some help to you.