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1990 Ski Nautique Dying

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Trickinainteasy View Drop Down
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    Posted: September-14-2020 at 4:46pm
Hello,

I am posting to see anyone could help me troubleshoot what is causing my friend's 1990 Ski Nautique to decrease rpm, sputter, and die at high rpm. This problem has been persisting on and off for the past two years. He has done the following with temporary alleviation of the problem but it has popped back up.

End of 2019
-Rebuilt Carb
-Drained Fuel Tank & Cleaned
-Cleaned Fuel Pickup in Tank
-Replaced Fuel Filter
-Cleaned Points
-Replaced Spark Plugs

For the better part of this summer it has ran well, but in the last month or so at high rpm it will run fine for a few minutes and then lose rpm, and sound like it is back firing. If we do not pull back on the throttle it will die. I am attaching a video of the boat being ran at WOT then dying.


 We cannot figure out if it is fuel or spark related. If we should start with new cap, rotor, and spark plug wires? Any advice would be much appreciated.
Thanks,
Nate
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8122pbrainard View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: September-14-2020 at 5:10pm
Nate,
To me it sounds like the engine is running out of fuel. You stated he cleaned the fuel pick up tube in the tank but did he look at the anti siphon valve at the top of the pick up tube. It looks like a barbed hose fifiing but inside is a ball check. They can get clogged. 




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SNobsessed View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: September-14-2020 at 7:44pm
Also try leaving the filler cap a little loose.  It may be drawing a vacuum if the vent hose is partially clogged.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baileys140 Quote  Post ReplyReply Direct Link To This Post Posted: September-15-2020 at 3:42pm
Have yall checked the distributor? I bought a 95 sn 351w pcm and it would run great, get up to 45mph then die suddenly and randomly. I replaced the distributor and it seems to clear up the problem
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 8:29am
Nate,
Will the engine restart immediately - or does it have to cool off for a period of time before it can be restarted?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 8:55am
Definitely running out of fuel and lean surge with pops
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trickinainteasy Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 5:29pm
Thank you for the ideas guys.

Baileys140 - We have not checked the distributor, is there anything we can look at that might tell us it is bad?

uncle-buck - After it dies the engine will immediately start up again. I'm guessing this is probably a good thing.

SNobsessed - We took the boat out for some trick sets this morning and on our way back to the dock gave it WOT with the filler cap loose. Still same result after about 10-15 seconds of running.


I am leaning towards the probability it is running out of fuel and going lean as well. But, after hearing that might be the case I am concerned we may have been causing damage by leaning the motor out at such high rpm, multiple times(it has been a lingering problem for the past two years). Is my concern warranted or do you think the motor is okay?

We are going to try and get to the anti siphon valve and clean it this weekend.
I will report back our findings!

-Nate
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 5:53pm
Well, one thing you can do is to run the engine from a portable fuel tank using new fuel hose while also bypassing the fuel filter. In other words, run the new fuel line straight from the portable fuel tank to the fuel pump. 

If it runs fine that way, then run it from the portable fuel tank through the fuel filter and to the fuel pump.

If it runs fine, that way, the issue is likely the anti-siphon valve or the fuel tank pickup. You wrote in your original post that you cleaned the tank and fuel pickup tube. Did you remove them from the boat? (I think you have to remove the tank in order to remove the tube.)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 6:21pm
In my experience witnessing many live with that way too long, is that no harm was done to your engine
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 6:23pm
What exactly was done to the pickup tube? Was it disassembled, or just inspected?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baileys140 Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 6:24pm
Originally posted by SNobsessed SNobsessed wrote:

Also try leaving the filler cap a little loose.  It may be drawing a vacuum if the vent hose is partially clogged.

would you be able to hear this vacuum as a very faint whistle when the engine is running?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 9:50pm
I doubt it but have not had this problem myself.  Sounds iike a vacuum leak but that doesn't make sense for hi speed failure.  Keep testing to narrow down the possibilities.  Fuel pump, carb inlet filter screen, collapsing fuel hoses - you need test plan to eliminate them all.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: September-16-2020 at 9:57pm
Start with the anti siphon valve- a common well known failure point that has these symptoms.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: September-17-2020 at 1:36am
If you think it's the anti-siphon valve, you can temporarily replace it with a regular hose barb. If the issue goes away, install a new anti-siphon valve. You can purchase a new one from Amazon for about $23. It's probably a 3/8 X 3/8 NPT.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: September-17-2020 at 4:51am
Originally posted by 8122pbrainard 8122pbrainard wrote:

Nate,
 did he look at the anti siphon valve at the top of the pick up tube 
Originally posted by Gary S Gary S wrote:

Start with the anti siphon valve- a common well known failure point that has these symptoms.  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: September-17-2020 at 7:38am
Every anti siphon I’ve seen cause an issue was pretty easy to spot once disassembled. Agreed that should be the first place to look based on the symptoms.
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