I had an '82 900F for several years. It was a great bike and gave me no problems. I put about 20,000 miles on it if I remember right. The main problem I heard about on the 81's was that they would pop out of gear. Honda had a modification that year that fixed the problem. Others have complained about cam chain tensioners, but I had no problem with mine. The engine was a lot quieter running than my '75 750F. Good power and smooth running. I had a Kerker 4 into 1 exhaust on it, with a SuperTrapp baffle with no discs in it. It sounded great and went like the proverbial raped ape.
My main criticism was that it had more motor than chassis. The brakes are fairly good (I used Ferodo pads) and the suspension wasn't bad for the day, but the frame wasn't any more sophisticated than the SOHCs, but there is a lot more power there. I believed the swingarm was inadequate. My experience with that bike has made me dis-inclined to hotrod my 750.