Does anyone know what the copression reading should be on a 1999 500 hp? I'm getting different stories from different people. Thanks.

The problem is that it will change as the engine ages. It also has to do with the compression ratio. I'd be guessing in the 140-160psi range. That said, I really don't think the compression reading is a statement of a engine's health. I've seen a 20psi difference equate to a 40% difference in leakage. If you are looking to do the test to help sell your boat, I'd wait and have the buyer do it at their cost. The leakdown test often reveals problems that you didn't know that you had. If the buyer does it, then you still have no (first hand) knowledge of any problems. Sometimes ignorance is blissful.

Well I thought I had a big motor problem but I'm hoping it will turn out to be just a carburator issue. I was putting the boat on the trailer on a faily steep ramp and all of a sudden a very dark brown smoke began billowing out of the starboard motor. I immediatly shut it down and took it to the mechanics. He did a compression check and found all 8 cylinders to be between 170-174. I thought that was good but he made the comment that the compression was way too high and that I should be running av gas in that thing. He said he's been doing this for 30 yrs and has never seen merc motors with that high of compression. I again started to get worried, but I talked to several other mechanics and they all said that the readings indicate a should have a healthy motor. So now I'm just hoping its something thats no big deal...like the carburator.

BTW, I called Mercury Racing as well and they say the out of the box reading should be 175.

Boat on a steep ramp = improper float setting if it's a carbed motor. Compression seems a little high, but if its not been an issue in the past, don't worry. Is it possible the ramp was so steep, the oil level in the pan was slanted WAY towards the back of the pan causing excessive crank windage? Extra oil thrown onto rear cylinders, pistons and oil scrapers cannot remove that much oil?

Just some thoughts...

does it still do it with the boat parked on a level surface?

Z

Todd,
Just a thought, since everything was ok all day long and it only happened at the ramp I would tend to think it is carb related. The black smoke seems to me to be excessive fuel. White is water, blue is oil. If it was just the way it was elevated on the trailer it could be an overflow of fuel down the intake. Check the oil to make sure that it is not full of fuel and if not take the boat for a sea trial and see how it goes.

You maybe ok.

Rick

readings like that should make you happy. Just cause your macanic has been in the biz for 30+ yearshow familiar is he with the blue HP motors? I get 200+ readings out of my 409 and it runs on super unleaded I also thick it is just the carb go now and fire it up on the trailer with the garden hose. Charlie

Well just got off the river. everything seems to be just fine. BOat ran fine. Guess it was just something with the ramp and maybe the carburator. Learned something neww this week thats for sure.

cranking pressures are directly related to camshaft profile. primairily overlap. your #'s look good