mine were 1995 500HPs with 440hrs, ran excellent! just pulled them apart this past winter and they still looked new inside! very reliable and a better platform to build on than the 502-415

I had a twin engine 1999 38' Scarab AVS with over 400 hrs(flawless),sold the boat and the 2nd owner ran them another 2-300 hrs and I believe he still hasnt rebuilt them,but his mechanic told me they are now way over due.

changed my springs at 150 hours now have 527 hours did have to change 1 distributer and 1 water fuel pump assembly. haven't fired them up this year yet, hope to soon.

I fired mine off today! First time this spring. Heading out in the AM to SML.
Mine are 95's with around 275hrs. I did a top end job just before 200hrs. They both ran great, at that point,but I didn't want to take a chance. I changed everything in the valvetrain.
I run 89 octane, also.

My 98's had a valve lifter "issue". The tie bar between the lifters fatigues and breaks, the roller lifter rotates and breaks grinding cam in process. This happened at WOT in the middle of a poker run. Needless to say **** all thru the internals of that engine. I redid both engines with new style lifters and retainers and 525 cams, complete rebuild on problem engine. I have had to replace the power valves on the carbs. They fail and allow the motors to run way rich. But after 7 years and 500 total hrs I would buy these motors again.

I had a set in my last boat 2000 fountain No issues!

Had a pair in my 99 Fountain. Great motors as long as you tend to the valve train at the proper times. Upgraded springs solve these issues. As for the loading up on long idle periods, Merc has them set up pretty rich, warranty deal, but it is very easy to pull a jet size or two out and clean them up. I'd own them again, and wouldn't call them a fussy motor to own.

And its not that the valvetrain needs constant attention every 200 hours. It was the original valve springs that there was an issue with and it wasn't recommended to run them past 200 hours (if I remember correctly). If you have swapped to an upgraded spring, I wouldn't think you would need to change them every 200 hours from then on. Might be a good idea to pull a valve cover and give a good inspection though.

Mine run flawless as well. They start almost as good as an injected motor. I did have a problem last summer that appeared on the surface to be a lifter failure. Once we got the engines apart it seems that a stuck valve may have been the actual culprit. Either way, freshened both motors at that time and I haven't had a moments problem since. Actually, may be upgrading them over this coming winter!!!

Lots of great posts! Sounds like the HP500 is a wise choice!