94 Ski Nautique Engine hesitation

The dirty plug is 1% towards being a problem, IMO.

Keep looking.

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

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.

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.

I plan to do it in gear. Seems to idle well in neutral then chug and die when in gear.

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.

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

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.

Well the most obvious reason is that it's hard to dunk the carburetor in cleaner unless you have a really big tank

A few other reasons though are

You can't check the tightness of the screws that hold the throttle body to the main body. There are 8 screws and there's a gasket between the main body and throttle body. It would be one of those leftover parts in your kit. I've seen plenty of screws that were not very tight at all allowing the gasket to leak. some. You find those 8 screws when you turn the carburetor over.

As mentioned before the gaskets on either side of the spacer should be checked and there's only one way to do that.

Did you take the secondary metering plate off so the secondary idle passages and main passages could be cleaned

Some gaskets, especially on the secondary metering plate are a royal PIA to get apart and scrape when the carb is on the bench and harder than that when it's still on the engine.

You get a lot better look at the idle transfer slots and curb idle discharge ports when the carb is upside down in your hands.and you can blow air backwards through them

There are other things too, but you get the idea

As far as power valves go, if you put back in the same size you took out, you're not screwing with the Holley calibration and that's generally a good thing.

If you don't know what it had you can find the Holley list # on the front of the air horn and post it and somebody will tell you what the original power valve was.

By 1994 there's a good chance it was a 2.5 but it's worth verifying.

Been away for a few days but still lots of good info.

First off, rebuilding the carb: You can pull both the primary and secondary bowls off the main unit, giving access to the metering plates and associated gaskets. Metering plates were cleaned/blown out, needle and seats replaced, power jet replaced, and jets cleaned/ blown out. The passages into the main body were cleaned with carb cleaner and blown out. Then reassembled with new everything. The carb body does not need to be removed to do that work. I did not remove the nozzel or j-tubs as there is noting to service. They appear to be flowing fuel just fine. For those that have done this rebuild, please tell me what part of the rebuild cannot be completed with the main body attached (other than the obvious manifold gaskets)? I'm not arguing, but I don't understand what part of the rebuild was missed by not removing the body. (again, excluding the manifold gasket).

With that said, the manifold gaskets could be an issue and I need to remove that from the equation by replacing it. No argument.

What is the consensus on the power jet size? I've read a ton and there doesn't seem to be agreement on one size.

Regarding the siphon or pick up tube: My thoughts were upon acceleration the engines immediate demand for fuel from the tank (pre fuel pump) would be at its highest for a second or two (highest vacuum on the fuel line). Once the fuel flow is stable (and not accelerating) any pick up issues might not be as noticeable.   Lightly suck on a straw with a hole and you might not notice the hole. Take a strong pull and you will suck air into the straw.....Might be flawed thinking but it made sense in my head. I need to try hooking up an auxiliary tank and see if that helps.

I can check these basics when I get to the boat but after that, I may be at the limit of my skill set. I can R&R parts but I still can't compare my abilities to those people that really know these boats and systems. There value is recognizing the minor issues that affect performance in a big way.

Thanks again.

You rebuilt the carb without removing it from the engine? I think we are all suspicious of this method or rebuilding a carburetor. A full removal and full rebuild would be a good first step. If you do this and it still hesitates, then we can move on to the fuel pump or the Pro-Tec. The write-up on how to install a Pro-Tec is linked in the FAQ.

+1 on what KENO said. Sure sounds like an accelerator pump issue. As recommended, I would take the carb off and do a complete re-build. Not terribly difficult and lots of material on the internet on the Holley 4160. Summit Racing also has good Holley carb videos.

I know that the ProTech system takes a lot of flak, but its justified in many cases. My 1994 had the "double trouble" of ProTec and the throttle body EFI. A ProTech system that is going bad can exhibit a wide variety of symptoms. And like many electronic components, the failure may not always be consistent nor predictable. It's a fairly simple change-out to replace the ProTech to a high performance distributor -- such as a DUI or Davis Unified Ignition HEI system. Lots of info here on that.

JQ

One test for vacuum leak is to spray carb cleaner on the suspect area, with engine running. If there is a leak the engine will sound different suddenly.

CRPilot wrote: ... Which gasket are you asking about? The float bowl, metering block, and primary to secondary tube o-rings were all replaced. ...

I assume Kevin is talking about the carb > manifold gasket. Or potentially, the carb to spacer gasket.

A bad (or flimsy) gasket there can cause a vacuum leak, which could give similar symptoms to what you are experiencing.

http://www.skidim.com/GASKET-CARBURETOR-SPACER/productinfo/RM0054B/

Quick question - did you replace the gasket when you installed the rebuilt carb?