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Discussion Starter #1
Purchased a 2004 XLT 1200 in February- had been winterized, power valve servo recently replaced, and cat d-plate kit installed, new spark plugs.

Ran great first two weekend outings, then this past weekend while running at speed RPM drops to 4000 rpm at WOT. Back at the dock a simple feel of the cylinder head indicated that rear cylinder had dropped out- it was warm while others were hot to the touch.

Pulled the spark plug and it was wet. Cleaned and dried the plug, back on the water and all was good for about 100 yards of running and then same thing. I have repeated this twice now.

Servo is actuating the power valves during cranking and power valve on rear cylinder is ok.

Suspicion at this point is coil pack, but would a coil pack fail intermittently? Any suggestions on what to check next?
 

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How many hrs on the ski or motor?
Have you checked compression on that cyl?
Is it still oil injected? If so check around in the bottom of the hull for oil. The line to the rear carb may have come off.

With this being an 04, I'm just betting the oil lines have never been replaced. And are quite hard and shrunk up and pulled off.
Of course this is just theory at the point based on experience.
 

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Thanks Dave for the reply.
I should know the hours, but I'm going to have to check to be sure. The ski is at my weekend place and I'm nowhere close for the next few days.
Compression on that cylinder is 120psi- consistent with the other two.
Still oil injected.

I'm new to PWC's so I welcome info on things such as brittle oil lines, etc. I know engines in general but the nuances of oil injected 2-strokes are new to me.
 

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The oil injection is pretty much bullet proof if properly maintained. That maintenance includes replacing the hoses from the pump to carbs every couple years. This is the systems weak link. As I said they get hard and shrink and break.
The pump is a variable ratio pump. Connected to the carbs by cable. At idle it's around 200/1. Helps keep from fouling plugs in low speed zones, and saves oil. At wot it's around 30/1. It also has a safety feature if the cable fails it opens up and over oils to save the motor and make you aware of issue.
 

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What's the compression on all 3 cyl's?
There's two possablities for your issue if that cyl is ok. It's either spark related or fuel. Fuel over delivery could be clogged fuel return orifice in carb, stuck needle valve. Or carb pop-off set wrong. Electrically it could be the ignition coil. Or the lighting coil that signals your ignition coil.
 

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Discussion Starter #6
I will definitely inspect the oil injection hoses first chance I get.

All 3 cyl show 120psi. I feel pretty good about the condition of the rear cylinder because just before that cylinder starts dropping out the ski runs like a scalded dog.

Can you get to the coil signal wire connectors from outside the electrical box? If so and the #3 hi-volts wire will reach to #2 cyl I thought I would try to swap #2 and #3 coils and see if the problem moved to #2 cylinder.

If not I guess I remove the electrical box to get to the coils? Can you pull the electrical box without removing other parts (exhaust, etc.)

I figure this will be an easier check than the carbs so do it first.
 

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Discussion Starter #10
Sorry for the delayed response. I have this pesky distraction called my job that has kept me away from troubleshooting.

My 2004 XLT is equipped with the crimp-terminal plug wires- not the type with screw-on boots. Since changing the plug wire required removal of the electrical box anyway I changed both the rear cyl plug wire and coil pack. Took the ski out for a test run- some warm-up laps around the cove and then WOT in the open water. For about 1 mile all seemed good at 7000rpm then when blasting back into the cove the RPM drops to 5000 rpm. Problem is back. I did notice that during half-throttle running there seems to be some "skipping" heard in the exhaust.

I can get WOT 7000rpm momentarily if I idle, move the fuel valve to OFF, let the engine starve and shut off, then move valve back to RUN, start the engine and go.

I'm thinking at this point I have fuel delivery or contamination (water) issue. Maybe siphon the fuel in the tank, replace with fresh, and replace the fuel filter?
 

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Maybe some crap in the tank getting picked up as it's getting sloshed around. You might need to empty the tank and clean it.
 

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May want to pull the fuel delivery unit out of the top of the tank and remove the flapper valve from the bottom of it. Sometimes they warp and get stuck closed and starve motor of fuel. That would explain the momentary rpm after turning ski off.
 

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Discussion Starter #14
Ok- I replaced the fuel in the tank with fresh and no change.

HOWEVER, after some more online reading and research I've believe I've pinned this down to a power valve servo problem:

Observing the power valve shaft during starting, the servo motor cycles as expected. Next, I placed a zip-tie on the power valve shaft so I could clearly see the position of the shaft. With the front seat cushion removed I took the ski for a test drive and during my first WOT run the power valve shaft moved to the "valves open" position and ski runs perfect. During this WOT run the power valve shaft rotated to the "valves closed" position (which from my understanding of the system it should not do this) and RPM immediately drops from 7000 to approx 4500. After this happens the servo will not move the shaft to the "valves open" position again- only after a cool-down period and then the problem repeats itself.

I'm convinced if I could somehow manually move the valves back to open position during the WOT run, RPM would go back to 7000.

I checked and cleaned the servo motor wiring connector and removed and inspected the servo motor. It was clean inside but the dc motor does have an overheated odor to it. The motor wire harness was routed such that the wires were pulled tight where they enter the servo motor housing, possibly causing a break in one of the wires. I disassembled the unit, cut the lead wires back and re-soldered to the circuit board inside the unit. Re-installed everything, ran the ski and the power valves still go back to closed position during WOT.

So- either the motor is bad or the signal from the CDI to the servo motor is bad.

Motor or CDI? Place your bets.
 

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Just purely a wild ass guess, but I'd say servo motor is bad. It's getting signal to open then overheating and closing. That's my guess. Should be able to find a good used on eBay cheep enough. New is $495. eBay 66v-85820-10-00 as cheep as $99. That way if it's not it you didn't spend a ton.
In your first post though you say it had a new servo motor. Why did they replace it?
Before you replace it though. disconnect the cables and be sure the valves turn freely. Should be relatively easy to open and close by hand. The valves have a tendency to sludge up and get very stiff. This will overload the motor and may be the issue. Especially if it's been run using cheaper end 2stroke oils.
Unfortunately, if this is the issue to clean them properly. will mean pulling each cyl and washing them out. Lube, and reassembly at same location.(cyl to piston)
Another thought, if the cables aren't adjusted properly may cause this also. In the neutral/closed position there is a small hole in the blk disc the cables hook to that should line up with an adjoining hole on cyl. (See attachment)
If it's out of adjustment it may not be able to reach it's valve open stop location. Causing it to go home after a few seconds or it overheats trying and goes home.
 

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Discussion Starter #19
Thanks for the adjustment info- much appreciated.

I purchased an Ebay servo motor- will install this weekend. Confidence is high that this will fix my problem.

The young tech at the boat dealership where I bought this ski told me that the servo motor had been recently replaced. This conversation was in January so "recently" was implied to be the previous summer. Unfortunately the tech is no longer employed at said dealership and the place specializes in boats/outboards- not PWC full service. They do winterize PWC's and of course sell used ones. As such the none of the remaining staff could offer much help on my issue or had much knowledge on the history of the ski. The tech did mention that the servo was replaced due to symptoms very similar to mine, but I shrugged the servo motor off as a culprit since it had been replaced. Oh well.

I checked the movement of the power valves, shaft, and control cables. Good news here- everything moves very easily. I think you may be on to something regarding the adjustment. I have not taken a deep dive into it yet but the servo motor travel does seem to be hitting a "hard stop" rather than moving to end of travel and maintaining a bit of slack in the control cables. I can see how this would cause motor damage due to overload. I will make sure adjustment is spot-on when I install the Ebay servo motor.
 
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