Why does my 25 horse Mercury Outboard Motor accelerate and plane out about 1/3rd of the time?

Question

Out on the boat the other day and when I gave it gas it sounded loud...but didn't plane out. Only about a third of the time when I gave it gas does it "sound right" and accelerate and plane out. The other times it sounds like it's sick (loud but not "humming") and doesn't accelerate up to plane? Any suggestions?

Answer 1

Take a look at the clutch pack between the lower unit and the engine.  It could be wearing out and slipping.

Answer 2

I'll go with cavitation, which happens if you give the engine to much throttle to fast.  Check the prop, but accelerate a little slower.  Good Luck!!

Answer 3

try new spark plugs

Answer 4

What throws me for a loop is the fact that it doesn't do it all the time- could be a clutch in the prop slipping, What it sounds like to me, is thick vegetation is getting on the prop and causing cavitation to occur- are you in grassy waters when it does this? Has the angle of the motor on the transom been changed? Prop changed out? Anything at all any different now then it was when it was running O.K.? Check prop for any damage, but we go back to the fact that it doesn't do it all the time- I think if you don't find it, give more information and let's try again.

Answer 5

Fuel Filter/Lines could be clogged or crimped.

Answer 6

sounds like cavitation   the prop could be damaged or the wrong size

Answer 7

Loud but not humming.  Don't understand.  Loud the same loudness?  just not fast?

sounds almost like cavitation or ventilation.

Have you made any changes in the hull?

Done any recent maintenance to the motor?

Check the prop and lower unit for any kind of damage or irregularity.

check the fuel tank for debris.  and water.

Make sure the tank vent is clear.

And a compression test.

What other symptoms?  starts ok?  runs good when it accelerates?