2002 0x66 225 loss of top end

[WVTERP]

I noticed about 2 months ago that my boat is topping out about 64 mph, sometimes even at 60 mph. This spring it would run 72mph. Only thing I have had done to it between those times is, I had the water pump and impeller replaced. It still comes out of the hole like I am being shot out of a cannon. The prop (fury 25p) is a little dinged but it was that way when it was running 72. I am going to have it worked on in a few weeks at Propeller Dynamics. Runs fine throughout the rest of the throttle range. Just stops gaining any oomph beyond 60mph. 90 percent throttle 60mph. 100 percent throttle. still 60 mph or so. only turning 5000 to 5300 rpms. in va, temps are below 50 for most of these runs, when I first noticed it was in Nov and it was about 65 degrees out that day. the motor does make a singing sound nnnnnNNNNnnnnnnNNNNnnnnnnNNNN instead of a constant sound. That is the only thing I have noticed that is different. Any clues? I just bought new fuel line and a new bulb yesterday, but I have not replaced them yet. I forgot, I did have the ignition switched replaced a few weeks before I noticed the drop in speed. I don't normally run the boat much over 60 so I don't know if this started before or after the switch was replaced, but I don't think it would be a contributing factor in the loss of top end.

[ClarkBird]

Compression test first and foremost, if it were mine. Then the usual suspects of O2 sensor, fuel filters and pumps, injector cleaning, new plugs, etc.

[CJ1]

Compression test first and foremost, if it were mine. Then the usual suspects of O2 sensor, fuel filters and pumps, injector cleaning, new plugs, etc.

Yep, a good complete service to start with and if it is running lean I would not run it like that or you risk cooking it. CJ

[WVTERP]

thanks guys. I appreciate the ideas. I will start with a compression test. Service guy who works on Yammahas also suggested that I check the spark as well, although it does not seem to be missing.

[CJ1]

thanks guys. I appreciate the ideas. I will start with a compression test. Service guy who works on Yammahas also suggested that I check the spark as well, although it does not seem to be missing.

Doubt it is spark. I found 3 bad boots on mine and it still ran fine. Andy at sim said he rarely finds electrical problems in the ing. On these engines. That is what it acted like and in my case was a injector out of spec at low rpms. Go through your fuel system including low pressure pumps. I am betting either them or a plugged screen. The 02 usually pulls hard then cuts back to 5k or so. If the 02 hasn't been replace in awhile it needs to be done as a maintenance item. Cj

[DLAB]

If the compression test checks out, it’s deff an O2 sensor issue, Low Pressure Pumps, or VST filter issue. In the very rare case that it’s an ECU issue, I actually have a known good spare that you could test, and buy if that ends up being the issue.

I’d start with the Low Pressure pumps. Loosen the 2 bolts on each pump, one at a time, and pump the bulb. If gas comes out the back you have a bad pump and should replace all 3. 90% sure this is your issue.

I have mine sealed off with an external fuel pump now, but before that I just changed all 3 every year, poor design, amd causes the headaches your describing