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Clunking sound in gear when just above idle


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2007 247 LSV with 383 hammerhead- 775hrs

Need some suggestions on what I need to check out to see what my issue could be.

Last weekend the boat ran great all day on Sunday, except one time while I was surfing the boat would not get above 10.6 mph when trying to get up on the surfboard. After dropping and the boat circled around it ran flawlessly the rest of the day.

Fast forward to this Sunday, I got one good surf set in then the boat started having issues.  Trying to pull the next surfer up, the boat struggled to get above 10.6 and started making a clunking sound right at initial take off then went away as the boat finally past 10.6 on up to eventually 11.4 mph.  After the surfer dropped, we really started trying to figure out where the noise was coming from. Sounds like either the floating wedge hatch or wedge is slamming down/up against boat a few times (except it's not the hatch or wedge since I locked it up) but doesn't cause vibrations and no smoke from the motor. When putting in gear, just above idle, we can hear it, then goes away as rpm's increase. Eventually the boat wouldn't crank, it turned over but would not start. Had to get towed in.  First I assumed it jumped timing or something, but today it fired right up in my driveway running with a water hose attached. Could rev up in neutral and never heard the sound.

I've checked the prop shaft, all bolts are tight. All oil levels are fine and are not milky looking.

The sound doesn't exactly sound like a rattle (been reading up on damper plate failure), but haven't ruled that out yet.

Any thoughts on easy items to verify before pulling to the dealer?  I did see 1 inactive code that said System 1.

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Found an old thread where someone had a clunking noise and replaced the cap/rotor which solved their issue.  Figured for $120 at Bakes it was worth it to give it a try.  Hopefully will water test one day next week once the package arrives.

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Still waiting on the distributor cap and rotor to come in, but did test the fuel pressure today.  Getting the 60 psi at keyup that is shown in the manual for the 383 hammerhead. Only ran it on a hose, so after replacing the cap and rotor, will check the fuel pressure while underway when I water test it.

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Changed the plugs, distributor cap and rotor.

Cap looked a little corroded.  Plug #3 was somewhat dry compared to the other plugs, and #7 was not even hand tight when I went to remove it.

I will be lake testing it tomorrow and crossing my fingers that this resolves the knocking noise I heard last outing and the no start.

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Water test went great, the knocking noise is no longer there.

I guess it just needed a new distributor cap and rotor along with some new plugs (NGK TR5's gapped at .045).

I guess with the 383 hammerhead, it may be worthwhile carrying spares.

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2 hours ago, justgary said:

Maybe spares, but a regular schedule to change them before they fail.  Then you can keep the most recently pulled one as your spare. 

I do plan on probably changing them every year even though I only put 50-75 hrs a season on.

Bought this boat last August and the plugs, cap and rotor had been changed in May.  The p.o. gave me the old ones.  Plugs did not look that bad, neither did the cap and rotor.  But, the cap and rotor looked just like the new one I installed from Bakes made by Quicksilver.  The one I just removed with all the corrosion did not, so guessing it was an automotive distributor cap and maybe that is why it corroded so fast?  I plan to clean the terminals to see if they were brass or what probably this week. I haven't seen any brands labeled either of the old ones, but the new one from Bakes came in a Quicksilver box.

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