Vibration and struggle under load

Already sought the expert advice of stepper459 on this, curious if anyone has had a similar issue.

Took the 93 sport out for a quick pull today. It started up and ran perfectly as it always does. Went out for a short ride and it got up and went with no issues, save for the usual drivetrain vibration I feel when coming out of the hole that evens out when on plane.

At the dock, I picked up 5 adults and we went out. I wakeboarded for about 25 minutes and everything seemed fine, except it did stall once as wife was putting it into gear to start one of my rides (it never stalls).

She said it started sounding "unsteady" but pulled me just fine.

I drove next, pulling a novice border who was struggling to get up and thus putting a lot of resistance on the boat. Something felt seriously off at that point. Major low frequency vibration felt in the seat/feet, and poor throttle response. Also it briefly sounded like either belt was loose and flapping around or like an empty solo cup was flopping around the engine bay (neither turned out to be true). We limped back in. I dropped off the passengers and went back out myself and everything felt fine, no more vibes, felt like a new boat. Steering was always good with no vibration in the wheel.

I dropped it off at a local nautique shop (race City) to have them look it over (respect that others would handle this on the trailer but I don't have the time coming up). Initial inspection notable for prop looking good, strut solid, tracking fins intact and strong, easy rotation of the prop shaft with one finger, normal trans fluid. I changed the sparks, oil/filter and fuel filter at layup last fall. Fuel stabilizer added too.

Thoughts on this? Stepper thinks spark/fuel related which sounds reasonable. I had been thinking trans or shaft alignment issue but perhaps not. Having a bunch of passengers/extra load on the boat seemed to be the major determinant.

KENO wrote: This must be a quiz of sorts to see if anybody knows what you have under the engine box I looked at your old posts and don't see any mention of a distributor or maybe a Pro Tec ignition system. Strictly a guess but I'll say you have a ProTec system and you also have a problem with one of the coil packs breaking down under heavy load. One coil pack feeds 2 cylinders and an issue like a breakdown of spark to two cylinders while the other 6 are good can lead to some bad vibrations. Hopefully I'm wrong and you have a distributor

Sorry about that - it's the original PCM 351. Pretty sure it's not a ProTec.

jimsport93 wrote: Would say you have a pretty good chance of having a Pro Tec ignition in that boat. Unless it has been changed out by previous owner. How about a pic of the motor.

I feel like a terrible boat Dad, but seems like I don't have any engine photos (and boat is currently an hour away).

jimsport93 wrote: How old are the plug wires? Have they been changed recently?

Can't say - having had the boat since last August, I have not changed them. I changed the plugs and thought the wires looked OK at layup last fall (but what do I know).

Here's a Pro Tec picture courtesy of somebody on CCF

Inside the circle is where there is a flat topped hockey puck looking thing is where the distributor would be if you have a normal non ProTec engine.

Inside the square are the ProTec modules with the plug wires coming out of them

No shame Tyler.
Get a pic when you can. Need to know what you have.

stepper459 wrote: I'm hoping the contacts on the distributor cap are just a bit crusty. New cap & rotor and off you go.

I'm going to be happy, while simultaneously regretting the labor hour charge, if that's the case.

DockDoc wrote: Concerning update here... the tech (who apparently is their older-nautique expert) found that cylinders 2 & 3 aren't firing, no compression

Since 2 and 3 are next door neighbors in the block, let's be optimistic and say it's gonna be a head gasket issue

Let's continue with the optimism and say that after the repair the boat will run better that it has since you bought it

We'll cancel that optimism then.   

I found an old post where you said it passes a compression check with flying colors when you bought it

Closing the chapter on this - lucky enough it turned out that the head gasket was blown. Shop replaced it, did an alignment, and along with a new acme 654 prop I just got back from lake test and she runs like a dream. Actually runs substantially better than previously, not a vibration to be felt and the power response night and day (I'm sure the prop helped). I'm suspicious that the head gasket was causing some loss of compression for a while.

Unfortunately, he did uncover some bad behaviors by the previous owner. Freeze plug had popped out, and they replaced it with a rubber one. Possibly related to that, the engine had badly overheated at some point. The muffler is damaged beyond repair from that so I'll be searching for a parted out muffler if anyone knows one. But, he felt like the carburetor was nearly brand new which I hadn't known, so that's a bonus!

For the amount of money I spent you'd think they'd have rebuilt the entire motor, but no they only did the starboard side.

I talked to the tech for over an hour (and for what it's worth the guy was amazing, really knows his stuff). He said he would probably do it if it was his boat, but didn't feel strongly about it.

I do have another gasket, I may just do it myself for the peace of mind.

KENO wrote: DockDoc wrote: For the amount of money I spent you'd think they'd have rebuilt the entire motor, but no they only did the starboard side. I talked to the tech for over an hour (and for what it's worth the guy was amazing, really knows his stuff). He said he would probably do it if it was his boat, but didn't feel strongly about it. I do have another gasket, I may just do it myself for the peace of mind. I'd say right about now, what's done is done, (or in this case would that be what's not done is not done) you're happy with the boat so drive it and enjoy it. If you have issues, you'll have a good idea where to start looking anyways

Yeah I think that's how I may approach it, we'll see. Runs so well right now I don't want to do much.