Can't Reach WOT and Top Speed anymore

[jasmo123]

Hello,
I have 97 Sea Ray 175BR with a Mercruiser 3.0LX. When I first got the boat it would reach a Top speed of about 42-43MPH with engine taching 4800RPM. This is at the top of the WOT range. I installed new plugs and wires after it started running a little rough. Still reaching same WOT just fine. Last trip out at the end of the day, I hit a hard wake and the boat started running rough again and would barely get to 4000 RPM. I changed fuel filter (went from ceramic to paper element), cleaned carb screen, and cleaned flame arrestor. I took the boat out again yesterday and it ran just fine all day low RPMS, high RPMs, pulling a tube, idling in gear, it turns right off when shut down. BUT now it will only reach just below 4400 RPMs and tops out at 38-39 MPH. The only thing I see is that there is a CAP missing from the top side of the outdrive directly above the prop where you access a bolt. This opens about a 1 inch hole where water can enter but gets trapped. Could this be creating enough drag to slow me down 3-4 MPH and consequently reduce my WOT by 400 RPMs? Please help I am kinda stumped. The boat runs fine but I've lost a little topend. I guess the only thing I haven't checked since start of season is compression but it was fine then all were right at 160psi.

 

[45Auto]

Re: Can't Reach WOT and Top Speed anymore

That little cap over the anode bolt isn't even in the water when you're on plane, so I doubt if it's slowing you down ...........

Was the boat loaded differently last time out? An extra person or some extra gear could easily make a difference of 3-4 MPH on a 3.0.

 

[jasmo123]

Re: Can't Reach WOT and Top Speed anymore

Hello ,

No boat was not loaded any differently. 2 adults and 2 small kids which is about what I normally have onboard. Even if I couldn't reach top speed though it still should have reached WOT. I would think. The only thing I can think of is when I installed the fuel pump the gasket contained holes that maybe were not oriented correctly? Now it is possibly restricting fuel flow? I don't know. I've heard of problems with accelerator pumps? The boat ran slick as a top its just not as fast and doesn't reach the top of WOT anymore.

 

[jerryjerry05]

Re: Can't Reach WOT and Top Speed anymore

Acclerator pumps are not in use at WOT.They come into play on acceleration.
Is the boat in the water or on a trailer? Has the prop been damaged?Has the fuel filter been changed? Check for water in the fuel.Re-do the comp test(if you can get 4400 then it's probably good).Jerry

 

[Out of Bounds]

Re: Can't Reach WOT and Top Speed anymore

have the prop redone. If it is alum the ears open up and will lose mph.

 

[mthieme]

Re: Can't Reach WOT and Top Speed anymore

Barnacles ?

 

[mcleaves]

Re: Can't Reach WOT and Top Speed anymore

I hit a hard wake and the boat started running rough again and would barely get to 4000 RPM. I changed fuel filter (went from ceramic to paper element), cleaned carb screen, and cleaned flame arrestor.

Sounds like you may have stirred up some crap in the tank and clogged the fuel pickup tube. Pull it and check.

M

 

[jasmo123]

Re: Can't Reach WOT and Top Speed anymore

The prop is Stainless steel. I recently pulled it and regreased it seemed ok. I just waxed the bottom of the boat no barnacles. When I installed the new fuel filter, I also removed the fuel tank pickup and cleaned with carb cleaner and it wasn't dirty. So I am at a loss. I used to go to 4800 and 43mph and now I only go to 4400 and 39 mph. I don't run the engine any higher than about 2500 when on the trailer. I only run it to WOT when under way on the water. Does anyone know if those little holes in the fuel pump gasket needed to be oriented a certain way? Maybe that is restricting fuel flow.

Again, boat runs great I can nail it from idle and it just takes off but just doesn't go as fast anymore. I guess I should just leave it alone but I know it can do better so I must tinker.

 

[chiefalen]

Re: Can't Reach WOT and Top Speed anymore

What the fuel pump giving you. 4-6 psi is what it should give you.

Hows the plugs look?

Hows compression?

It doing anything else running hotter than usual?

 

[jasmo123]

Re: Can't Reach WOT and Top Speed anymore

I changed the plugs at the begining of the season. They have maybe 20 hours on them. I haven't looked at them recently. I haven't checked compression since this started. As I said the boat ran very rough until I changed fuel filter, cleaned carb screen, cleaned fuel tank screen, and cleaned flame arrestor. Now it runs as smooth as a top it just won't reach full WOT or Top speed it used to reach. Like somethings holding it back? I don't have a fuel pressure gauge so I don't know what fuel pressure is. I will check plugs and compression maybe this weekend. I am just at a loss.

 

[mcleaves]

Re: Can't Reach WOT and Top Speed anymore

Interesting problem.. Could the timing have jumped with the hard pounding? I am just trying to think of things that can happen from big bounces and impact. If the distributor wasn't tight it could have moved.

M

 

[jasmo123]

Re: Can't Reach WOT and Top Speed anymore

I am not sure about the Timing. But you would think if the timing was off that the boat would run rough at some other time? I will put my hands on the distributor though and see if it is at all loose. That is a good thought.Thanks.

 

[jasmo123]

Re: Can't Reach WOT and Top Speed anymore

Ok so the distributor is tight but I don't have a timing light so I didn't check that yet. I did check compression and for me all were right at 150psi (155,147,145,144) which I think is fine for the 3.0. So anyway, I am still wondering if I put that fuel pump filter bowl gasket in improperly and am somehow restricting fuel flow. The manual did not really show any particular way of orienting it so maybe it doesn't matter.