1978 Ski Nautique Problem

Alright guys...I need some help here. My girlfriend's family has a 78 Ski Nautique with a 351 Commander in it. Here's the problem: We start it up and run it for 30-45 minutes and everything is fine. After it heats up for a while, it'll start to idle rough, and eventually sputter, and eventually die. If there is an load on it (someone skiing), When you give it gas to pull the skier up, it sputters and hesitates pretty bad. They just replaced the carb on it and have it tuned up, and her brother replaced the water intake hoses on it today. We took it out for a while, and it's doin the same thing. We tried to pull my girlfriend up and her brother gave it gas and it hesitated, and so she dropped. He left the throttle wide open and it took about 200 feet for the boat to actually catch up to where the throttle was. We've been working on it all day and can't figure out what the F the problem is. Any ideas?

Thanks!

 

Sounds like the carb is not jetted correctly??

 

when you say it heats up does the temp gauge go sky high? or what do you mean?

 

Or could be the wrong carb all together. In my last job I saw people constantly putting on carbs that were way to large for the application.

 

Was this an issue before the carb was replaced?

 

does it run 100% for the first 30 minutes? because i'm thinking it might be that its not getting enough water.

 

It runs perfectly. Crank it up and gun it, and it's fine. Feels like nothing is wrong with it for the first little while. It can pull up a skier, stop, idle, gun it again and it's fine. It doesn't start doin all that until later. Like I said, they replaced the temp sensor tonight so they're gonna take it out tomorrow while I'm at work and run it for a while and see if the temp shoots up while they're skiing. We played around with it tonight and it seemed like there was plenty of water comin in to cool it. That's why I'm so confused.

They found some ethanol free gas and have been running it in it for the past couple tanks, but that hasn't helped. I thought maybe the ethanol has been gumming up the engine/fuel lines? They put some Sta-Bil through it last week but it didn't help anything. I'm lost on this thing.

 

but if it was a fuel problem you would think that it would be instant not take 30 min to start sputtering. you got a weird problem.

 

EXACTLY. Haha. We can't figure out what the heck it is.

 

well good luck. get back at us when you figure it out.

 

Thanks. Will do. I'm hopin they get it figured out while I'm at work tomorrow so I can get some wakeboarding in this weekend.

 

I don't know why but for some reason I am thinking electrical or maybe they put the distibutor in wrong if they removed it.

 

Hmmmm...possibility.

I know I smelled it today, but we had just filled it up a little earlier, so I figured he might have spilled some or something. I honestly haven't paid that much attention to that any other time. What was your problem?

 

No rush. It's bed time for me, anyway. . Thanks, though! I'll check back in the morning.

 

I've had spark plug wires that were cracked do this kinda thing. Runs fine, then heats up and sputters (it's grounding on something)

I don't know.. take a look, actually found this at night one time.. saw the spark.

 

Thanks guys. I told him to check all of that this morning. I haven't heard anything from them, so I don't know if they got it runnin or if they've checked those or not yet. I've been at work all day so maybe they got it runnin. I'll find out tonight I guess. May have to spend my Friday night goin over there to help work on the boat.

 

Sounds like you just need to cut your ties, accept that it's a lost cause and just give me the boat, I'll dispose of it for you

How's the spark plug gap? Distributor cap and rotor?

 

I'd check the plug wires with a multimeter and check the plugs.

 

Does it continue to runrough after you start it back up or does it smooth out? If it is still rough I'd still be looking at vapor lock. Check the routing of the fuel lines and see if some insulation is neded.​

 

Distributor cap was just replaced. They replaced the plugs a couple years ago...way before it started acting up.

They checked the plugs yesterday and everything seems fine. Checked the wires for cracks or anything weird and didn't find anything.

Yea, it still runs rough unless you park it for a little while and everything cools down. There's a fuel overflow outlet on the side opposite the gas cap, would that not act as a release valve, too?


I've got a wedding to go to today so I won't get to help em with it, but whatever they did to it yesterday really screwed it up. They took it out this morning after they replaced the coil and it died on them and woudln't crank back. Got back and realized it was out of gas. All the gas leaked out somewhere. When the Bilge pump kicked on it was mostly gas coming out. This is according to my girlfriend who is NO WHERE CLOSE to mechanically inclined.