Lack of rpm

[Locke]

I went out for a cruise in the boat yesterday (2000 Sea Ray 270 7.4L Mercruiser Bravo 3). The lake that I keep my boat on has some floating debris due to recent rains; this may be coincidental to my problem but maybe not. I left the slip and the boat got right up on plane and cruised at around 4000 rpm. After 20 minutes I dropped back to 1500 rpm for an hour, during this time at low speed I heard a few minor bumps from submerged logs I assume. When I pushed the throttle forward I could only get around 3500 rpm and couldn?t get on plane. I felt a little bit of vibration but only when I attempting WOT. I tilted up the outdrive and inspected the props and no apparent problems, the props are SS.

I had some friends with me so I couldn?t spend much time troubleshooting but when I go back to the lake what should I look for to figure out the problem?

Locke

 

[Don S]

Re: Lack of rpm

Check the fuel filter for any water. When was the water seperating fuel filter replaced last, last tuneup etc.?

 

[Locke]

Re: Lack of rpm

I just purchased the boat and prior to putting it in the slip I had the engine/outdrive gone through so probably I have about 10 hours since all new fluids and filters.

 

[Don S]

Re: Lack of rpm

Still check the fuel filter. Water in the tank will get into new filters just as well as old.

 

[Locke]

Re: Lack of rpm

Will do

 

[magster65]

Re: Lack of rpm

Yep... sometimes the water seperator is skipped during maintenance... ya' never know. Have a closer look at the props again too. Turn them by hand and see if they wobble or anything. If you heard debris bumping against the boat, you may have hit your prop and bent a blade slightly or (hopefully not) bent a prop shaft.
We get the same thing here during high tides or storms... it's like a slalom course sometimes

 

[Mischief Managed]

Re: Lack of rpm

If your 7.4 is anything like mine, bring some fuel on board to pre-fill the new fuel filter. Mine won't self prime.

 

[Fireman431]

Re: Lack of rpm

Also check the hull of the boat, if you were bumping logs & debris in the water. Why couldn't you get on plane @ 3500 RPM? That should produce enough speed to do it. Were you properly trimmed?

 

[Locke]

Re: Lack of rpm

This is a relatively heavy boat and when I want to get on plane I trim the bow down, go WOT until about 4300 rpm and then trim the boat more bow up and pull back to around 4000 rpm. When I noticed the problem WOT only got me to around 3500 with some vibration and I wasn't gaining anymore rpm. I'll do a little more investigation on the outdrive and olso check the water seperator.

Locke

 

[Don S]

Re: Lack of rpm

Are you sure the drive was actually trimming up when you hit the button?