94 Ski Nautique Engine hesitation

I'm looking for some help from the local experts. I've been chasing an engine hesitation for more than a season now and I've given up with the local dealers who "can't duplicate" the issue.

94 Ski Nautique PCM 351 Carburated with about 450 hours. The engine starts and idles good but can be a little cold blooded typical to carb'd engines. Once warm, but not completely head soaked, the engine will have a very distinct cut out when pulling a slalom skier up. More throttle = more cutout.   After a second to two it catches and pulls up to and maintains cruising speed. Hard acceleration from 25-36 will trigger the cutout as well. A slow, low load acceleration will not cut out.

It feels like someone pulls the tether for a second (checked that though ans its tight).

After skiing for a bit the cutout gets worse as the engine completely heat soaks. At its worse I can't even pull skiiers up. At that point it feels like its missing on a cylinder or two.

The carb's been rebuilt (by me) which had no impact on the issue what-so-ever. I wouldn't rule out carburation thought as it feels like a fueling issue to me.

I've read a ton and there seems to be a list of potential issues but I honestly don't have the right tools or in some cased the mechanical expertise to diagnose the problem if I'm staring right at it.
-Fuel pump - original
-Fuel filter (replaced last year)
-Fuel tank check valve?? (not sure what that is)
-Accelerator pumps?
-Probably many other possibilities...

That's where I need someone that is good at trouble shooting. I'm located just west of Milw Wi. Does anyone have a recommendation for a person/mechanic that I can take this too? Or anyone close by and willing to meet me on a local lake and trouble shoot (when the ice goes out)?

I don't want to loose another summer to frustration.

Looking forward to getting this solved.

Jim

I'm not from around there, lots of people in your area. But, when you say you don't have the expertise, I'd be very surprised if someone who successfully rebuilt a carb can't do all of the above troubleshooting themselves. Nothing of course wrong with getting some help though!

Thanks for the vote of confidence on my abilities! I've raced motorcyles and rebuilt my own 2-stroke and 4-stroke motorcycle engines for 20+ years so I have the basic skills to attack some of these issues. What I lack in the specific knowledge of how the 351 fuel and ignition systems work. Not the same as a single cylinder thumper...

Forgot to mention this is the Proboss HO so it has the protec ignition. No points to check and to my knowledge no wear parts to replace. Not sure if there are other validation checks for it.

Yes, I reset the accelerator pump squirt per the spec'd gap. Don't recall what the spec was but it was checked and there is a solid squirt of fuel when moving the throttle open.

My boat is currently in storage but I'm taking notes of what to check when I can get to the boat:
-Recheck accelerator pump adjustment
-Anti-Siphon valve (hoping there is a "how-to" on line somewhere)
-Fuel pressure - What pressure should it be and are there any in-line gauge kits that would be recommended?

It'll be 3-4 weeks before I can get to the boat to start looking at this but if anyone is looking for a fun spring project I have one....

It took 14 minutes for somebody to blame it on the Pro Tec system.

Slow day on CCF

For CRPilot google 'Correctcraftfan Pro Tec and do some reading.. You've got a few weeks to get thru it all   

Whether it's the problem or not, it'll scare you

I'll read more about the Protec as the thought has certainly crossed my mind. Right or wrong, the reasons I haven't concluded its it protec:
1. The issue exists when stone cold, right off the trailer. But the issue does get worse as everything heats up.
2. The dealer "tested" the protec ignition after an hours worth of run time on the boat (fully up to temp) and didn't detect any issues with the protec (and to be fair found no issue at all. ...)    

Did this issue come on like a switch or was it a gradual progression?
When not towing a skier if you ease into the throttle just right will the motor eventually allow full throttle at some point?
From what I've read it sure sounds like fueling, when you rebuilt the carb did you use a "Holley" marine rebuild kit? If so that kit would've likely came with two power valves so I will assume you replaced your old one with one of the new ones.
If you know four stroke motocross bikes than you well know the awesome Keihin FCR-MX carburetor. That carbs accelerator pump tuning is absolutely critical, so try to treat your boats Holley in the same fashion.
Just my 2 pennies!

Good luck man!

Gary S wrote: There is a saying, 90% of carburetor problems are electrical.

And about an equal number of ignition problems are carburetor/fuel

Lots of great info guys. Thanks. I have a growing list of stuff to check.

Answer a few of the questions:
1. The engine only hesitates for a few seconds or less. Once it pulls through it has never had an issue revving right to top speed (~47 ish).
2. It has never gone into limp mode.
3. Yes, it was a Holley Marine rebuild kit. but it only came with one power valve. I don't recall if it was the same as what I pulled out but I do know that there was a ton of online chat about which one to use. If it was changed by one size, would that trigger an issue? The hesitate was there before the rebuilt and was actually the reason I rebuilt it. I didn't notice any performance change after the rebuild.

I never had to deal with the FCR. I ran two strokes (38PWK) until the 4 strokes were EFI. EFI just makes life easy vs jetting for weather and altitude.

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

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/

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.

+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

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.

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.

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.