Motor Problem

[livetofish28]

So we have a 1989 Yamaha 150 pro v on the back of a 1999 stratos 273 vindicator. We normally run with a 23p merc trophy and run about 5300 rpms wide open at 57-59 mph. On a recent trip to the chickahominy River we noticed that the fastest we could get it to go was 52 and it was falling on its face trying to get on plane. After inspection upon getting home I noticed a small crack in the blade of the prop, and thought that might have been the problem. Switched the prop to the old 25p 3 blade that we used to run 59.5 on at 4700 rpms only ran 53.5 at 4300 rpms. I'm out of ideas guys. I have a huge tourney coming up on April 25-26 that I need it running good by. Any suggestions would be awesome.

Tight lines

Andrew

[Way2slow]

Help depends on how much you already know.

First thing is to do a leak-down test, or compression test if you can't do a leak-down. All six cylinders should be within 5% from the highest to lowest, absolutely no more than 10%.

The next thing is going to require be able to read plugs. After running at WOT, (down the lake) for about three minutes or more, then pulling the kill switch or shutting it off without letting off. It's best to do the shut down while heading toward the ramp. It's a lot easier when you are not used to pulling plugs on the water to load the boat and get it on dry land. You have to load without cranking motor. Pull each plug and check the color, they all should be the same color, usually about the same color as a brown paper bag or a little lighter. If any are dark or black, that cylinder has a problem. Keep track of the plugs so you know which cylinder each one came out of.

You might start with replacing the plugs, but not until you have read the old ones. New plugs are vry hard to read unless you are an expert at it.