1993 Sport Nautique grief - Help

[laddski]

Newbie here,

I have a 93 Sport Nautique that I have owned and loved for 4 years now. It has the ProBoss 351 HO with the Pro-Tec ignition and Holley carb.

I did the usual plugs, oil change and impeller at the beginning of the year and got 3 great morning runs out of it. On my 4th trip out, we pulled away from the doc and it ran fine until we hit exactly 2400 rpm and then the motor ran like an out-of-balance washing machine. Regardless of how much gas I gave it, it just got worse. I put my tail between my legs and loaded up and went home. I pulled the plugs and they were black after only 8 hours of running. Carb is too rich which I knew since this is a CA boat running in Utah but I ran plugs all last year with NO fouling at all. I replaced the plugs again, thinking I might buy time but to no avail. Still hitting the 2400 rpm barrier and it is exactly the same every time. I have not messed with timing or anything else, yet...

Anyone have any ideas? It starts and seems to run perfect right up until I hit 2400. Carb gone bad? (Holley 4bb) Ignition problem? I just want to get back on the water. Any ideas or help would be greatly appreciated. There is a long back log at the boat repair shops and I am a DIY'er anyway. Thanks.

Ladd

[efox]

I had similar problems on a 92. The point that mine started to falter was at 3000rpm.

First question, did you find that there was any backfiring noises? If you did, you will certainly need a new power valve in the carb. Also, check to be sure all of your plug wires are on the correct plug. You can check by removing one at a time while the boat is running. Any on that does not cause the engine RPM to drop is in the wrong place or is not firing. In that case you need to replace the coil pack.

Eric

[laddski]

Thanks Eric,

I don't get any backfiring. I thought about pulling the plug wires but got nervous as I've been shocked before. I think I will do it anyway. The coil pack is a good possibility.

Ladd

[efox]

It's of small consolation, but it only hurts a little...16 times! Hopefully you find the culprit quickly. They happened to be the last couple I checked. I have now made a diagram and have a digital photo. SKIDIM told me the wires are good for a 1000 hrs, though I think there are a lot of people changing more frequently. Good luck.

Eric

[M3Fan]

Could also be a distributor problem. The timing should change ever so slightly with increases in RPM- I think this is done with small weights spinning around on the distributor shaft. Just a thought.

[laddski]

Problem Solved (I think) thanks to SKIDIM. I have two posts on here, one is the above and the other is that my Red Light is on that signals an oil pressure or temp problem. Called SKIDIM this morning and they said the two are related and that Nautique has built in a limp mode to prevent damage and that either my temp sender or oil pressure sender are bad and quickly told me how to check. Cudos to SKIDIM. They know their stuff. I will post tomorrow with the result.