boat has hard time getting on a plane

[hyuncher]

I have 2001 Cobalt with 5.7 GSI/Volvo Penta DP-SMTD 1.95 (3869036) and having some issue with cruising RPM and getting the boat on plane. The engine has ~400 hours.

My boat never had any issues but last week I noticed slight RPM variation at the cruising speed of 25MPH. (3000RPM to 3200RPM, not much but noticeable)
I stop the boat and tried to plane again but that boat had hard time planning this time. It appears that something is gear drive is slipping. The engine would rev up but the boat would not go.

To be safe, I just put the boat on idle speed and trying to get back to shore. I cruised at idle speed for about 15 minutes or so and try to plane again and I was successful and came back to shore cruising lowest plane speed as possible. (~20MPH, distance of 2 miles) If I went higher, the RPM would go up and down again. (3000-3300RPM)

I was thinking it may be a fuel issue but I only use ethanol free fuel with stabilizer. I am leaning towards my dual prop or something is slipping on my outboard drive.

One incident happened last year on my prop last year that I want to point out. I moor my boat all year and one-time last year, the water level went down far enough, my prop hit the bottem rock and was bent slightly. I noticed this last year but I use the boat for 4-5 times this year without any issues.

Could this incident damaged the prop bearing? Could this cause prop to be our of balance to cause this type of slippage? If it is not a prop issue, what else I should check to resolve this issue.

Any input will be greatly appreciated to resolve this issue.

Thank you in advance...

 

[Starcraft5834]

thinking your prop hub might be slipping... take off prop and inspect hub for wear/slip

 

[hyuncher]

Thanks for your feedback. I am planning to take the boat out of the water this week and check the prop. Please let me know anything else I should be checking.

 

[Starcraft5834]

if your out drive gears were failing, you'd hear that problem loud and clear.. failing prop hub is my guess.

 

[hyuncher]

My problem may be the fuel pump. Look the discussed below. Sounds like my problem

Symptoms of fuel pump failure...?

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1997 Mariner 200xl

Returning from offshore when motor lost power in the inlet
Never died, will idle smoothly, will rev fine when not in gear, just has no power

When a load is applied, when I try to get up on plane, there just isn't enough power to get it done

I figure...
if there was a fire issue the motor wouldn't idle very smoothly, if at all
if there was a carb issue motor wouldn't idle smoothly

I have...
replaced all plugs
drained fuel water seperator
changed fuel filter

Problem still exists.

Any suggestions?????

Re: Symptoms of fuel pump failure...?

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On an I/O engine, with an electric fuel pump, at a steady setting of the throttle, you will see the RPM needle wander up and down very slowly. You might not hear any difference in the RPM's. This is the first signs of a "fuel pump going south"! I have the pump changed every two years, (going into the third season), as part of general preventive maintenance. A weak fuel pump can cause your engine to run lean and "lean" = "hot"!-------- Greg

Re: Symptoms of fuel pump failure...?

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I had the same problem. Idled fine but would not run under power. Turned out to be the fuel pump(s).

RE: Symptoms of fuel pump failure...?

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First thing to check is the anti-siphon valve located right off the fuel tank. They are a weak spring, little ball check valve that has caused many to scratch their head as you are.

Next I would ensure that you have no air leakage on the suction side of the fuel pump including hoses, primer bulb, fittings all the way back to the tank.

Next I would check the fuel pump. I believe your engine has a pretty accessable one that you can pull apart with a straight slot screwdriver. You will find (I think) a mesh screen filter right there as well just by taking off the center screw.

 

[hyuncher]

I think when I rev up, it tries to rev up but it can slow down and loses power. I don't think the engine speed stays high. It drops down. I need to check again in the water but I was not paying close attention when I try to get on plane.

 

[Shaper79]

So have you found any think out.