Last year, I acquired this 1992 Yamaha 4AC. The previous owner only used it for about 5 hours each year. It came with the original manual and tool kit. Not a bad deal for €90 I would say.
I changed the impeller, and when I pulled down the lower unit, I noticed that it had not ever been previously removed. All edges and bolts were still sealed with the factory paint! The impeller was of course shot (what else do you expect after 31 years), but luckily, all pieces of it were found.
I also adjusted the carburetor, put in some fresh gear lube, gave everything a good clean, and I put new water resistant grease on all moving parts.
It starts very easily and it runs well. I did a compression test and got 160 psi. This motor still has all the factory honing marks visible in the cylinder. My other 4AC that saw a lot more use produced 163 psi, so I think this low hour motor could increase its compression a little after some running. The 4hp models have slightly higher compression than the 5hp models. This motor has a factory reccomended mix ratio of 100:1 with TC-W3 oil.