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Discussion Starter #1
I’m looking for some knowledgeable help with my 2005 WaveRunner FX. I have had this machine for two summers now with no issues. When I took the ski out last week it fired up with no issues but after we launched it I noticed that when you hit the throttle the engine would rev-up but the ski didn’t jump up and go, as if the intake was clogged. If you increased the throttle slowly everything worked and you could hit the normal top speed of 50 to 55. Then after a couple minutes this loss of power went away and everything was fine. So I thought that maybe there had been a clog of weed in the intake.

At the end of the day when we were putting the machine back on the trailer the loss of power came back, but once again only when you hit the throttle fast. When the throttle was squeezed slowly everything was fine. On top of this when I got home and checked the engine out I found there is some water in the oil, not a lot but some, and the forward most cylinder sparkplug is firing but burning very black. The engine still fires right up.

Are these issues related or are they two separate problems? I know my way around an engine fairly well but have no experience with these engines.

I could use some good advice on where to start.
 

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I'd change the spark plugs as a first step.........very common problem on the FX and the running trouble sounds much like a fouled plug. Water in oil may actually be gas in oil. Did it look milky?
 

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Discussion Starter #3
Ernest, I can see a fouled plug giving bad performance but why would it cause the ski to be propelled only slightly while the engine is still revving at full RPM? Is there a belt that connects the engine to the jet propulsion or is it a direct connection?

The oil is very slightly discolored, but not like milk I’ve seen before. The level on the dipstick is up about an inch or two but I didn’t smell it to see if it was gas. What would cause gas to leak into the oil?

I’m on the east coast and it raining buckets today so I’ll recheck the oil when it dries up.
 

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Ernest, I can see a fouled plug giving bad performance but why would it cause the ski to be propelled only slightly while the engine is still revving at full RPM? Is there a belt that connects the engine to the jet propulsion or is it a direct connection?

The oil is very slightly discolored, but not like milk I’ve seen before. The level on the dipstick is up about an inch or two but I didn’t smell it to see if it was gas. What would cause gas to leak into the oil?

I’m on the east coast and it raining buckets today so I’ll recheck the oil when it dries up.
Sounds almost like a wear ring. Did it feel like a clutch slipping when it revved and didn't go?

That would be the belt you were reffering to.

I am on the upper Chesapeake Bay, and it is pouring.
 

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Discussion Starter #5
That is exactly the way it felt, like a transmissions or clutch slipping. What is a wear ring and how hard is it to change out. Is this something that should be replaced on a regular basis? And could this or does this have anything to do with water or possible gas in the oil?
 

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On Yamahas they call it a "Jet pump housing insert" here is a link Watercraft Parts: Jet Ski Wear Rings - Watercraft Superstore you can purchase them. You only need to change them when they wear out and give you the symptoms you have and it only gets worse like a bad clutch. My understanding is that it protects the impeller from damage. Sort of like a sacrificial lamb in the drive train.

Good Luck............
 

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Change the plugs first. Then change the oil, I won't be surprised if your issues are all gone.

Don't borrow trouble. You might be surprised how slightly fouled plugs can really mess with your head.
 

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Change the plugs first. Then change the oil, I won't be surprised if your issues are all gone.

Don't borrow trouble. You might be surprised how slightly fouled plugs can really mess with your head.
+1

Fouled plugs make this ski run really weird.
 

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Discussion Starter #10
Thanks Ernest, I can give this a shot it’s quick and easy and hopefully it will do the job. If it is just bad plugs though how do you explain the water or gas (it’s been raining for days here and I haven’t opened the ski yet) in the oil, this part just doesn’t make since to me? Do you agree with Outlaw that the wearing could also cause the loss of thrust, although once again I’m at a loss for the oil problem?
 

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If you have a cylinder not firing due to a fouled plug that results in lots of unburnt gas that can eventually find its way into the oil.

I agree that any damage to the impeller or wear ring could result in loss of thrust. The wear ring on the FX is stainless steel, not plastic like other skis, so it is pretty durable, unless you have sucked up rocks, or other debris.

If you are still having problems with loss of thrust after you change out the spark plugs, take off the intake grate and have a good look at the impeller and wear ring. look for nicks and dents in the impeller, and check the clearance between the blades and the wear ring (I think is should be around .45 mm or less on that ski).
 

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I had the same happen to me a couple years back. Changed the oil and fouled plug and ran like new after that. The same thing happened to it again about 4 or 5 months later after i sold the ski. New owner changed oil and plugs and off again....strange problem to have twice in a 6 month period but I guess an easy fix so can't complain too much. They must be prone to this problem
 
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