75 mercury 2 stroke losing rpm’s under load in water

[Connerbrown56]

I’ve got a 1999 75 mercury 2 stroke, it doesn’t run WOT when I started Saturday was only getting 3500 rpm’s, since then I’ve done every basic repair that can be done. Near fuel pump diagram, new spark plugs, a coil pack, new fuel lines going to fuel pump, new gas new oil, compression check was 100 psi on all 3, cleaned carbs out. Took it back out yesterday ran better was getting about 4800 to 5000 rpm’s still lacking about 1200 rpm’s. Outside of being put in the water it runs and sounds great without being put under load, as soon as it gets put into the water it doesn’t do the same as on land with the water ears on it. I did notice a small chugging noise at idle speed about 1500 rpm’s where it sounded like the engine was struggling to get enough gas or air but I’m at a stand still now not sure what to check or do next. Any help or advice would be great thanks in advance.

 

[racerone]

Check the reed valves.

 

[Connerbrown56]

Check the reed valves.

I checked the reed valves they were good and intact. Took it out yesterday had it bog completely down on me. Only way to get it to 5000 rpm’s was to lower the trim all the way and then bring it back up slowly to level run

 

[racerone]

How did it run for you last season ?-----Run with a timing light to check for spark as you speed up.------Run with cover off the front of carburetors.-----Use a STRONG flashlight and observe fuel coming up from nozzles.----Compare the amount.-----Then again it could be an issue with cylinder sleeves.

 

[Connerbrown56]

It would run full speed, had an issue with the motor Turing off on occasions but start back up believe that was related to the bad coil pack I found. It’s 24 years old so I don’t expect it to run top notch speed anymore but just a few weeks ago it was running 40-45 mph and yesterday it was only running at 25-28 mph. We’ve had issues with water in the fuel in the past I’ve treated it and ran new gas threw it already 2 or 3 times. Just trying to understand why it runs so good out of water and so bad under load in water it’s definitely frustrating

 

[racerone]

Well----It is NOT running good out of the water.----It just sounds like it is to you.-----It will bark / roar like a lion on 2 of 3 cylinders.----.-----But the prop does NOT need to do any work spinning in air.----Sounds like it is running on 2 of 3 cylinders.----In my opinion it should be easy to figure out where the issue is.

 

[Connerbrown56]

I’ll get some videos and upload them in a few days