2000 Challenger twin 787 loss of power and top speed

[janzalone]

I just replaced the impellers on my boat, put it in the water and everything was going great. It took off with great acceleration and hit about 53 MPH had great power even in a turn. After a few weeks I took the boat out one day and one engine will only get up to about 5000 RPM on one engine and about 6000 on the second engine. Now the boat looses power when I turn. It seems to have decent power when I take off out of the hole, but lacks any kind of top speed, all I can seem to get out of it is about 40 MPH. I took the pumps back off and one of the rattle cones had water mixed in with the pump oil, im not sure if that will make a huge difference. I did a compression test and got about 145 PSI out or each cylinder on both motors, I changed the plugs too and that didn't seem to work. The wear wrings are not gouged up or anything they are still the same ones that were in the boat when I bought it, I just replaced the impellers.

 

[Dr Honda]

Unless the bearings in the pump are seizing up... a bad pump will allow the engines to rev high, and lose top speed.

Since you are losing top RPM's... there is something else wrong.

1) Does your buzzer work? (possible over heating)
2) is your fuel system clean? (possible fuel starvation)
3) the pump with water in the bearings... does it spin free? (possible bearing seizure)

 

[janzalone]

Well I took the pumps off yesterday and the impellers spin nice and smooth although I noticed the exhaust pipe to the muffler pulled apart and I could see black exhaust where it was leaking. I'm thinking that with pressure built up in the cone on one pump that had water in the pump cone and the exhaust leak together might be the culprit. I'll fix all that and report back. If you can think of anything else let me know, thanks for you help!