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94 Ski Nautique Engine hesitation

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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: March-17-2018 at 8:19pm
Good points on the carb. I rebuilt it the first time without know exactly what I was lookinf for.

From the last post, no, I’ve never had issues starting it. Fires right up every time. I was just pointing out that with the carb it can be a little cold blooded until it warms up good. Like others mentioned, if I dropped it into gear when cold it will stall out sometimes. Once it’s warm it typically doesn’t do that. I thought that was normal but maybe not.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: March-17-2018 at 9:52pm
Carburator issues can be baffling - there's quite literally dozens of possibilities. If it's not a vac leak, could be jet issues. If not that maybe acc. pump or perhaps needle seats. A buddy chased an issue for 2 whole seasons only to find out his electric choke was malfunctioning - after a carb rebuild (twice) and replacing pumps and fuel lines and filters.
Anyway, I know absolute zero about the protec so I can't speak to that. But honestly, it sure sounds like a fuel issue to me, and specifically sounds like an over-fueling issue in some respects (loading). Have you checked the condition of the spark plugs when you're having these issues?   Didn't think I read anything to that effect. Might not be anything but it only takes a few seconds to pull a plug immediately after an episode. Normal? Or wet.....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: July-23-2018 at 1:16pm
Hi Guys, Sorry for the long hiatus. Its been a cold spring in WI and it took a while to get the boat in the water. So here's the latest:

I pulled the boat out in spring and dropped it in the water to test. Yup, the hesitation and rough idle were still there. I drained all the fuel and replaced it with fresh gas. At the same time I pulled apart the anti-siphon valve and checked it. No issue there as it was clean and moved freely with very little pressure.

Test drove again with new fuel and still hesitated with rough idle but I could slowly nurse it up to full speed.

I was lacking time and patience so I decided to take it to a local repair shop that seemed to have a good reputation. The owner also owns a 93 prostar 190 with the same PCM 351 so he was familar with the engine and its characteristics. They checked the basics like fuel pressure, compression, spark, and it all looked good. When checking the carb they found the throttle valve bushings to be worn which was allowing a vacuum leak. While they said it can be repaired, but recommended replacing as the parts and labor to do so were almost as much as a new one..   

I was happy to hear they "found" the problem so I authorized the repair.

I took the boat out after words and right off the trailer it wouldn't idle. In neutral, it was ok but drop it into gear and it would sputter, chug and quit. I'm pissed at this point. I take it back and explain the issue. They water test it and "can't duplicate the issue". I get the boat back and find they turned the idle up to 1100 rmp and it now pushes a wake at idle. Not good for maneuvering around down skiers....

I then found out they never tuned the carb. Bolted it on and called it done. (stated they come preset). Long story short, I turned the idle down and manually adjusted the idle mixture screws out (counterclockwise) 1/8 of a turn each and it will now idle at 900 in neutral and 700 in gear. Better. The idle is still a little rough but it works. I plan to buy a vacuum gauge and set them properly.

So I hop on dry land, grab a quick dinner and decide to put the boat back on the trailer for the night. When heading out to the boat launch I accelerate hard like pulling a skier and the engine falls flat and misfires for 4-5 seconds (just like before the new carb) and then picks up and runs strong til top speed. I repeated the test a few times and it hesitates every time now. Friggin back to square one and the carb does not appear to have been the problem at all!

I will say that with the new carb the engine runs really smooth and strong once past the hole shot. It easily pulls 46-47mph with a nice consistent pull. So the new carb isn't a total waste, but it didn't fix the issue I've been chasing.

So when it hesitates it feel like its missing cylinders and does not accelerate. Then like someone flips a switch, the power comes on and it pulls strong and smooth. It does not "transition" it just switches from flat to full pull.

So I need to ask: What does limp mode feel like? I'm now back to the protec and intermittent issues. The dealer is also out of patience as they "can't duplicate the issue" and I'm tired of paying them $100 an hour to not find anything.

I'm thinking of just replacing the protec but I guess I'm hesitating as I really don't know for sure thats the problem. I could easily spend another $500-700 on the ignition and not solve anything.

In the ignition and electrical space, I'm out of my league. (little to no working knowledge to test those systems)

What the recommended next step?

Thanks for listening

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: July-23-2018 at 1:30pm
Long shot, since you're having a similar issue with both the old and new carb, but it's a free and very simple fix.

Have you dialed in the adjustment for the accelerator pump on the new carb?
Specifically the clearance between the accelerator pump diagram arm and the operating lever screw: https://youtu.be/k-Nx5HEzvlY?t=1m20s
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: July-23-2018 at 3:14pm
I skipped a little bit of the story in that I had the boat in the water 3 times with the new carb and the acceleration was perfect. Just chasing the lack of idle/rough idle issue. Because of that I think the accelerator pump setting is ok. It came out of the hole just fine for three trips to the lake.

Then when I adjust the idle mixture screw 1/8 a turn and I get a hesitation.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: July-24-2018 at 2:03pm
I've seen some say it's better to get your idle dialed in with the boat in gear (under load).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: July-25-2018 at 11:09am
I plan to do it in gear. Seems to idle well in neutral then chug and die when in gear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bri892001 Quote  Post ReplyReply Direct Link To This Post Posted: July-25-2018 at 11:19am
Also, make sure you double check for a vacuum leak, as mentioned by Snobsessed on page 1. Not sure if this was mentioned, but it's preferable to use the marine specific base gaskets to help to avoid vacuum leaks https://www.skidim.com/GASKET-CARBURETOR-SPACER/productinfo/RM0054B/
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: July-25-2018 at 8:06pm
On the Holley carbed boats I have owned I found the ski boat idle worked better when I left it slightly rich. The adjustment screws on either side of the carb could be adjusted for a good idle on the trailer but in the water I would open them up maybe 1/2 to 3/4 turn each and the in water idle would be much stronger and not die or chug.
It also started better without touching the throttle.   Slightly rich but seemed to be the answer in my Holley carbs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: July-26-2018 at 11:14am
Exactly...and generally good advice for all carbs

Adjusting idle mix No-load by max max idle rpm method will produce an off-idle lean stumble and warm starts requiring throttle input.

setting idle mix in forward gear set the most , stable, resilient and torquey idle, which produces minimal delta in rpm when placed in and out of gear.



decades ago, if your car had an automatic transmission, idle and idle mix was set in gear, precisely for this reason
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."

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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: July-30-2018 at 1:40pm
Thanks all.

I set the idle on the trailer and then dropped in in the water to reset it in gear. Its much better but not perfect. I think its just my tuning may not be dialed in yet. (First time ever setting the idle with a vacuum gauge). It no longer dies but it does drop a little rpm. I'm finding that the best vacuum while in gear pushing through water comes at about 3/4 turns out from full in. That sounds off from just about every "how to" I've read that suggests the sweet spot should be 1.5-2.5 out. This is starting out at the lowest idle possible without stalling to avoid pulling fuel through the transfer slots. Its nets a healthy vacuum of 16-17 inches.

Even with the idle set I'm still getting an intermittent engine miss on hard acceleration. Its only after I follow this routine:
-Start up cold off the trailer (no problems)
-Warm it up good/use it for skiing 30-40 minutes (no issues)
-Shut is off and go swimming/whatever for 25-30 minutes so the whole engine bay heat soaks.
-Start it up and it will no longer accelerate smoothly. Off idle the engine sounds like its missing cylinders for 3-4 seconds then clears up and appears to run ok. I can run it top speed and repeat and it still hesitates (just to make sure its not a fuel load up issue).

I'm thinking about just ordering a new ignition and pull the protec. While I can't seem to prove that's it for sure, I also can't prove its not. Another summer 1/2 gone and its still not right.

Now DUI or the SKIDIM package: I need to read pros and cons about each.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2018 at 2:24am
No disrespect to Vince and the folks at Skidim, but the DUI is a much better system in my opinion.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-31-2018 at 9:07am
Originally posted by Jonny Quest Jonny Quest wrote:

No disrespect to Vince and the folks at Skidim, but the DUI is a much better system in my opinion.

JQ


You must have some reasons you could list for him JQ

By the way you might notice that SkiDim sells the DUI distributor now for 351 RH rotation engines. Strangely enough they don't have the normal rotation version listed on their website
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CRPilot Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2018 at 11:39am
ok. Spent some more time yesterday just checking the basics so I can throw the boat in the water and test/disconnect the oil pressure, water temp, and knock sensors to see if that eliminates the issue. I also pulled the plugs to check condition and gap. I found something that looks strange to me but not sure if its normal. The two plugs on each side towards the front (of the boat) are perfectly clean, almost new looking. The rear two plugs are brownish. I would have expected them all to be very similar.

Is this normal or a sign of a tuning issue?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2018 at 2:45pm
The dirty plug is 1% towards being a problem, IMO.

Keep looking.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: August-02-2018 at 10:27pm
Originally posted by KENO KENO wrote:

Originally posted by Jonny Quest Jonny Quest wrote:

No disrespect to Vince and the folks at Skidim, but the DUI is a much better system in my opinion.

JQ


You must have some reasons you could list for him JQ

By the way you might notice that SkiDim sells the DUI distributor now for 351 RH rotation engines. Strangely enough they don't have the normal rotation version listed on their website


When I started my ProTec swap-out project a couple of years ago, I started out by ordering the Skidim kit. After getting the kit, I was unimpressed, particularly when I compared the Mallory distributor to the DUI unit. I returned the kit back to skidim and went with DUI. One 12V feed wire and 1 tach output wire. Done.

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2001 Ski Nautique Open Bow
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Aqua skiing, ergo sum
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