96 XP Revival

[JeremyD615]

Lol. Well I feel like the world’s biggest moron right now. I’m pretty sure I found the problem, and it’s the rectifier. There was no E-Box in this ski when I got it, but I had one in my bin of spare parts that came with the 95. The previous owner used to have a 96 as well, and said some of the parts were spares for that ski. Sure enough, there was a complete E-Box for a 96 there. I only opened it up to verify the part number on the MPEM and didn’t pay much attention to anything else in there. When I just pulled it to test the diodes with a multimeter I noticed that there’s an empty space where the rectifier should be. That would explain my battery not holding a charge long, and I’m assuming it could cause the high rpm issue, but on the other hand, it really should run strong until the battery voltage drops enough to cause a weak spark. Do you guys think this may be it, or should I keep digging into the fuel system as well?

 

[Matt Braley]

I'd try it with a good rectifier in there. The lack of one definitely wasn't helping.

 

[JeremyD615]

I just finished putting a new one in. I had ordered one to keep as a spare since they seem to fail fairly often. Looks like I’ll need to order another spare!

I really didn’t want to post anything when I found it was missing, but it’s the stupid mistakes that we seem to learn the most from, so I’ll take some heat in the interest of spreading some knowledge...

If the weather cooperates, I’ll try to put it in the water tomorrow and see what it does.

 

[JeremyD615]

Well I finally had a chance to mess with this thing and get it back on the water. I installed a new rectifier, bypassed the fuel strainer and selector valve by connecting the reserve line to the carb inlet with an inline filter in place, and I went ahead and pulled the carbs again just to make sure the filters were clean and I didn’t miss anything. Everything checked out in the carbs. The pop off is 35psi on both carbs. It was about 38psi, which is at the higher end of the range, so I massaged the arms slightly until they were even with the carb body. They both hold pressure indefinitely, and the pulse line fitting holds 3-4 psi indefinitely as well. I set the low speed screw to 1-1/2 turns out on both carbs, and the HS screws to 1/8 mag, 1/4 pto. Since i was showing some lean symptoms before, I wanted to richen things up and make sure I had my bases covered.

The result: hesitation from just off of idle to 1/2 throttle, and it ran great from 1/2 throttle to wot for about 10 minutes, and then started the random shut off at full throttle again.

I pulled the plugs when I got it out of the water, and they both look lean now, with the mag side being a little leaner than the pto. This has got me really confused since I went quite a bit richer on the carb settings across the board. I was hoping the missing rectifier was the issue, but it definitely appears to be fueling now. The only modified part of the ski as far as I can tell at this point is the choke plate removal, but I can’t see that alone requiring the carbs to be adjusted farther out than they already are. I guess my next step is to pull the fuel baffle and double check the screen in there, but I have a feeling that’s not going to be it. Anyone have any other suggestions?

 

[mikidymac]

Well I finally had a chance to mess with this thing and get it back on the water. I installed a new rectifier, bypassed the fuel strainer and selector valve by connecting the reserve line to the carb inlet with an inline filter in place, and I went ahead and pulled the carbs again just to make sure the filters were clean and I didn’t miss anything. Everything checked out in the carbs. The pop off is 35psi on both carbs. It was about 38psi, which is at the higher end of the range, so I massaged the arms slightly until they were even with the carb body. They both hold pressure indefinitely, and the pulse line fitting holds 3-4 psi indefinitely as well. I set the low speed screw to 1-1/2 turns out on both carbs, and the HS screws to 1/8 mag, 1/4 pto. Since i was showing some lean symptoms before, I wanted to richen things up and make sure I had my bases covered.

The result: hesitation from just off of idle to 1/2 throttle, and it ran great from 1/2 throttle to wot for about 10 minutes, and then started the random shut off at full throttle again.

I pulled the plugs when I got it out of the water, and they both look lean now, with the mag side being a little leaner than the pto. This has got me really confused since I went quite a bit richer on the carb settings across the board. I was hoping the missing rectifier was the issue, but it definitely appears to be fueling now. The only modified part of the ski as far as I can tell at this point is the choke plate removal, but I can’t see that alone requiring the carbs to be adjusted farther out than they already are. I guess my next step is to pull the fuel baffle and double check the screen in there, but I have a feeling that’s not going to be it. Anyone have any other suggestions?

Those plugs in the picture look almost perfect if not a little rich. If they were lean they would be dry and white.

 

[JeremyD615]

Those plugs in the picture look almost perfect if not a little rich. If they were lean they would be dry and white.

They look quite a bit darker in the picture than they do in person. The plug in the first photo is pretty close to perfect, but looks a touch lean to me. The electrode on the second one looks good, but the insulator is like an off white rather than brown.

I may just run my other motors richer than I need to, but these look way lighter on the insulator than I’m used to seeing.

 

[GGuillot]

I set the low speed screw to 1-1/2 turns out on both carbs, and the HS screws to 1/8 mag, 1/4 pto. Since i was showing some lean symptoms before, I wanted to richen things up and make sure I had my bases covered.

Go a little richer on the highs, see what happens, can't hurt to run it a little rich to see if you can get it to stop shutting off at WOT. Same issue last year for me on a newly completed resto on the 97' GTX, I did this, eventually backed the highs all the way to 1 turn, the no change revealed a problem with a brand new fuel selector as soon as I bypassed it. I know you've bypassed, but I'd at least try it.

 

[mikidymac]

You should never have to go any further on the highs. If it is shutting off something is wrong and richening up the highs isn't going to fix it.

 

[JeremyD615]

I just can’t figure out what else it could be. The only other things I can think of that I haven’t checked and double checked are the fuel baffle, the coil in the rear ebox, and the Y on the fuel return lines. When I did the carb rebuild, they passed the pressure test individually, but wouldn’t hold pressure when they were all reassembled. I found a crack in the plastic Y on the fuel return, so I replaced it with a 1/4in T fitting, and everything held pressure then. I can’t imagine going from a Y to a T fitting would cause enough flow restriction on the return to cause this, but it’s the only thing that’s changed since it ran right on the big end. Any thoughts on that or suggestions where else I might look? I think the hesitation from idle to 1/2 throttle can be tuned out, but the shutdown and lack of rpm up top is what has me stumped.

 

[GGuillot]

You should never have to go any further on the highs. If it is shutting off something is wrong and richening up the highs isn't going to fix it.

From a trouble shooting prospective, that's the whole point of richening and backing the highs out more, to see if there's an effect or change. Not to necessarily fix it, but to see if it's a variable or not.

In my case it had absolutely no effect, so I turned my attention elsewhere.

 

[Matt Braley]

Well it's time to look at a couple other possibilities. These things do happen.....

1- Broken baffle in the waterbox. Sometimes they come loose in there and clog the flow.
2- Soft rear exhaust hose. They can delaminate and get real squishy so pinch it and make sure it still has some integrity.
3- Ignition pick up bracket. The first series of brackets would/will break off sometimes. Before they do they will crack and be half torn. This makes them run but do crazy things.

 

[JeremyD615]

Well it's time to look at a couple other possibilities. These things do happen.....

1- Broken baffle in the waterbox. Sometimes they come loose in there and clog the flow.
2- Soft rear exhaust hose. They can delaminate and get real squishy so pinch it and make sure it still has some integrity.
3- Ignition pick up bracket. The first series of brackets would/will break off sometimes. Before they do they will crack and be half torn. This makes them run but do crazy things.

Well you might be on to something there. The rear exhaust hose doesn’t appear to be torn or leaking, but it is pretty soft. I can grab it between my thumb and index finger and squeeze it shut with very little effort. Has anyone come up with a replacement part that works? It looks like the hoses aren’t readily available anymore.

I shook the water box around to see if I could hear anything moving around, and didn’t hear anything, but I have another water boa for it in my parts bin, so I may just go ahead and swap it to check that off the list as well.

Is there any good way of checking the pick up bracket without pulling the mag cover? I’ve never had to remove a cover with the motor in a ski, but it looks like it’s quite a job.

I also did a compression test just to rule that out again, and it’s perfectly even between cylinders. I just have a cheap harbor freight gauge that reads WAY low, so I can’t verify an exact number, but they are even and read significantly higher than my perfectly running 717, so I think I’m in good shape there.

 

[Matt Braley]

A good used rear hose is probably about 40-50 shipped. Westside Powersports had 100% silicone ones made once but I think those all sold. He will have a used one though I'm sure.

I'd try everything else before the bracket check. If you take it on you can pull the front mount and wedge it under the engine to keep the front up so you can get to the bolts.

 

[JeremyD615]

Well I ordered what appears to be a good used hose. I’m going to go ahead and replace the water box as well since I have a spare. On the subject of the water box, I noticed that at idle the line from the regulator to the pipe is partially full of water, but it doesn’t start flowing until the throttle is opened. Is that how they normally operate? I was under the impression that I should have a steady flow until the revs get up to the point that the valve starts restricting the volume. I don’t want to burn up a new hose, so I figured I’d ask the question.

 

[mikidymac]

At idle the cooling system flows very little water, You need to get the rpm's up a little to see good flow.

 

[JeremyD615]

Well I’ve been going back through everything trying to catch anything I might have missed, and something caught my eye. The water flow from the regulator just seems too slow to respond to throttle, so I dug up the cooling system diagram and I think the lines are backwards on the WCV. The top fitting, closest to the red cap, is routed to the T fitting on the larger hose, and the bottom fitting is routed to the pipe. It should be the other way around should it not? I did change those lines out, but I’ve been super careful to only take one off at a time and put them back exactly where they came off. They must have been routed this way from the start, so I bet it’s been overheating the exhaust the whole time I’ve had it.

I’ve only run it long enough to test each change I’ve made, and since I’ve never had it running right, it’s only been run for short periods each time it’s been out. I’m surprised I haven’t completely melted a hose yet, but I’m sure if I had kept going it would have. How stiff should the exhaust hose be? It’s really soft now, but it’s not completely collapsed. With any kind of negative pressure, I’m sure it would close, but I would think the exhaust would create positive pressure, especially at higher RPM where the ski is shutting off. I’m going to fix this as soon as the parts come in, but it seems like an odd cause for a high rpm shut down, so I’m probably still going to have a gremlin to chase down.

 

[Matt Braley]

Yes water goes in the bottom and out the top. There are arrows molded into the plastic on the regulator. That is a breakthrough.

The rear hose is laminated. The inside will bubble up and flop around in there when it's running. We know yours has been hit with too much temp many times so I would definitely swap it out.

 

[JeremyD615]

I’ve got a new hose on the way, so hopefully that will get me back up and running! I can’t say enough how much I appreciate all of the insight and help you guys have given! I’ve probably still got some bugs to work out, but I couldn’t have gotten this far without the support I’ve gotten from everyone here!

 

[JeremyD615]

Well I got the new exhaust hose and water box on today, and no change at all. It’s still breaking up at lower throttle settings and shutting off up top. I’m at my wits end with this thing. Before I pull the mag cover off and check the pickup bracket I think I’m going to go through everything one more time. It seems like I’ve gone through everything that could cause this problem, but I’m about out of ideas. I did notice that if I hold the throttle at a steady position, say half throttle, it seems like it moves between two distinct power levels. It will go from a steady 5000rpm for a few seconds and then drop down to 3500rpm and stay there until I blip the throttle. It’s not a surge, as it doesn’t go back and forth. Power just falls off like a switch was flipped, and it comes back as soon as you open the throttle plate more. I also realized today that I need to get another dess key programmed. I’ve only got one key tied to this Mpem, and it’s got a crack in the rubber that seems to be growing. Anyone have any ideas before I start going through the carbs and rave valves again?

 

[GGuillot]

Well I got the new exhaust hose and water box on today, and no change at all. It’s still breaking up at lower throttle settings and shutting off up top. I’m at my wits end with this thing. Before I pull the mag cover off and check the pickup bracket I think I’m going to go through everything one more time. It seems like I’ve gone through everything that could cause this problem, but I’m about out of ideas. I did notice that if I hold the throttle at a steady position, say half throttle, it seems like it moves between two distinct power levels. It will go from a steady 5000rpm for a few seconds and then drop down to 3500rpm and stay there until I blip the throttle. It’s not a surge, as it doesn’t go back and forth. Power just falls off like a switch was flipped, and it comes back as soon as you open the throttle plate more. I also realized today that I need to get another dess key programmed. I’ve only got one key tied to this Mpem, and it’s got a crack in the rubber that seems to be growing. Anyone have any ideas before I start going through the carbs and rave valves again?

It seems it ran fine earlier in your thread, but I'd try clipping the spark plug wires back a little and see what that does. I think it's a stretch, again, it seemed to run fine, but the check rotary valve timing, it could be slightly off. Or check for excessive play in the rotary shaft, this could cause run issues also.

I'm only brainstorming ideas....understand that level of frustration chasing an issue.

 

[Matt Braley]

Ride it with the seat off and look for smoke or water spraying out. If water is not close then try to rig the hose to feed the system like the pump does. Tie it in behind the water regulator and see how things look as the engine is running with good water pressure on it.

Take lots of pics too. Give us something to study and we can better point things out. A video while riding would be great but that can be hard to do safely. If this is in the thread somewhere then oops. I'm just popping back in and didn't go through the whole thing.

 

[mikidymac]

Keep in mind that the 787 will act funny around 4,500 rpm where the engine sounds different and bumbles and stumbles a little especially if you try to get it to do it. This is the throttle position where the RAVE valves are opening and the carb is transitioning between circuits. I can get every single one of them to do it but it is just the way they are.

 

[JeremyD615]

Thanks guys! I’m in the process now of going back through the carbs again and making absolutely sure all of the internal passages are clear.

I did trim the spark plug wires, are there was no change. I haven’t checked the RV timing since it started acting up, but that will be on my list.

I ran it with the seat off for a few minutes yesterday. There’s no smoke or water leaks that I can see. I also seem to have good water flow from the regulator now. I’ll try to get out and take a video. We will see if I can manage that without dropping my phone in the lake! There’s a fishing tournament at the ramp where I put in this afternoon, so I’ll have to try to get through these carbs and beat them out there.

I know the raves cause some changes in that 4-5k range when they open up, but this is far more significant than that. It will literally drop 1500 rpm all of the sudden cruising with a constant throttle position.

 

[JeremyD615]

So I pulled the carbs again today and ran ran a full can of carb cleaner through the low speed adjuster, the high speed adjuster, the pilot jets, and the main jets just to be sure something wasn’t partially plugging the circuits. No real change on the water, though I did seem to get one or two good passes without it shutting down. The low throttle position hesitation is as bad as ever though. I managed to get a couple of short videos, so maybe you guys hear something that points me in one direction or the other.

The first video is right after I got it warmed up and out past the no wake zone. This is a gradual pull on the throttle so that you can really hear the stutter. Once it got past that point, it picks up immediately for a few seconds before there is that rpm drop. It goes from about 4700 to 3600 instantly.

The second video is with the throttle pinned from idle with the shutoff coming quicker than it normally does, but it shows how it happens. Normally I can let off and it will catch itself at about idle rpm and stay running, but it dies completely here.

This last video was immediately after the shutdown. I pinned the throttle again and it ran fairly smooth without shutting down. Notice that I’m only pulling about 6300 rpm with it pegged though.

Any ideas?

 

[Matt Braley]

Your oiler is oiling right? Just making sure that you have seen smoke and confirmed the flow.

My next move would be to try different carbs. I've had some that just would not run for some reason so I make sure to mark or discard those carb bodies. It's rare but it does happen. There is still the spark pick up possibility also. With that one you could put a cheap spark tester inline and watch it while it's running before you tear in.