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  1. #1

    Help! '01 GP800R hitting rev limiter - don't think it's cavitation

    I have had the carbs rebuilt on my 01 GPR 800, as it was having difficulty starting from cold and the last time I had it out, it began losing top speed (on dream-o-meter, but gives me an idea).

    The engine is stock, rebuilt around 40 hours ago (ski now shows 182 hours) with good, equal compression and PV`s and recently rebuilt pump.
    Only mods are Riva intake grate, trim tabs, ride plate, PPK and Solas prop.

    In the past, the dream-o has usually read around 100-110 kph on glass, but this time, the Max I could get was around 80.
    Then 70ish and on the limiter, then 60ish and on the limiter, accompanied by a vibration, which seemed to be coming from around the intermediate shaft area.

    I was heading back into the harbour at this point, as I wanted to get it off the water.

    I quickly fired it up, on the trailer and at less than half throttle, it was heading for the redline.
    To me, this discounted the impeller etc as a possible issue.

    I consulted with a couple of people and one guy who knows his stuff, said it would be the carbs at fault.
    I was thinking more along the lines of damaged impeller or shaft, but the carbs needed attention, anyway.

    I sent the carbs off and removed the pump and intermediate shaft so I could inspect them.
    All seems fine.

    I never measured clearance - but it was miniscule - and the impeller and wear ring still appear as perfect as they were when repaired around 20 hours ago. The ski hasn't sucked anything up, since.

    So I threw it all back together, with new B8RES plugs, it ran fine on the hose, so I hit the water with a friend and his Seadoo XP.
    Mine now starts up straight away and trawls happily and felt alright in the chop.
    On the river, though it has the same top end issues as before, on the rev limiter at 70-80% throttle and it transpires that 45 mph GPS is the best it can now do and that damn XP was way faster.

    It also didn't seem to use much fuel in the 2 hours/23 miles we covered. Only two bars.

    Could lean running cause it to hit the rev limiter?

    I really don't think it is cavitating from a dodgy pump, as I have experienced the 'slipping clutch' sensation before and I don't get it, this time. It does feel a bit sluggish from the hole shot though, I guess.

    Could it be a coil or the stator breaking down at high RPM?
    Tomorrow I intend to check the electrics and see if my results are within spec.

    I don't claim to be an expert with ski's, far from it. I know my way around a tool box and with cars, but with these things, I am all ears.

    Any ideas? This thing is pissing me off, now (I have done/had to do way more to it in the past, including a full respray, so would like it to behave, now)

    Come on, I got my ass kicked by a SeaDoo. LOL

    Thanks, Liam.


  2. #2
    I will test the coil packs etc tomorrow.

    Could this actually be a misfire? Has anyone else had similar issues?

    I would appreciate any input/ideas.

  3. #3

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    You should check the plugs and see if they all look the same. You could have a coil going bad or a bad plug wire and a different looking plug could tell you which one. Also, shut it down after riding it faster and feel around the cylinders. They should all feel about the same temp. If one is colder then its the one not firing well.

  4. #4
    Quote Originally Posted by LT1GMC View Post
    You should check the plugs and see if they all look the same. You could have a coil going bad or a bad plug wire and a different looking plug could tell you which one. Also, shut it down after riding it faster and feel around the cylinders. They should all feel about the same temp. If one is colder then its the one not firing well.
    Thanks.

    Will have a dig about, after work.

  5. #5
    My multimeter is knackered, so I couldn't test the coil etc, tonight.

    Here's the condition of the plugs. New 2.5 hours ago.



    Very oily. Is this due to running premix?
    The electrodes basically look the same, though. Slight difference in the colour of the ceramic parts. No.1 on left, no. 2 on right.

    I removed the pump, too. So I could use a feeler gauge to check the clearance.




    0.025mm feeler gauge is all I can get in between prop and wear ring, although as can be seen, it won't fit in all the way around.
    It seems to wear ring isn't fully circular?



    As can be seen, the prop is in perfect order. The wear ring itself has a few dings and marks, but was deemed serviceable by Jet Shed, when they re-pitched the prop.

    Surely this is an electrical issue that I have. Or maybe reed or power valves?...
    I also want to compression test the motor, again.

  6. #6

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    I don't see any sealer on the pump housing where it goes into the transom plate on the engine. Did you have sealer in that area? It looks like it is all painted black. That whole area has to be clean and have sealer on it when put together and the shoe has to be sealed to the transom plate as well. I re-read your post and you think you might be hitting the rev limiter but are going slow. What RPM is the tach showing? If you can hit the rev limiter you are not missing obviously.

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  8. #7
    Quote Originally Posted by LT1GMC View Post
    I don't see any sealer on the pump housing where it goes into the transom plate on the engine. Did you have sealer in that area? It looks like it is all painted black. That whole area has to be clean and have sealer on it when put together and the shoe has to be sealed to the transom plate as well. I re-read your post and you think you might be hitting the rev limiter but are going slow. What RPM is the tach showing? If you can hit the rev limiter you are not missing obviously.
    You are right, there is no sealer on the pump housing to transom. I was told this didn't need to be sealed - although it makes sense to me that it should be.

    The transom and shoe are sealed to the hull with 3M 4200 and the shoe is flush with the hull bottom.
    Although I have gaps between shoe and hull and shoe and transom if you look through the transom from the back of the ski.
    Should I also run a bead of sealant around here (so that inside of the transom is completely smooth)?

    As for the pump, should the mating faces on transom and pump, be clean and have a bead of sealant, sealing them to each other? What about the voids in the face of the pump, just leave them?

    The JP parts are black, because they and the ski were originally white, when I got it and I wanted them to look better.
    If they were still bare alloy, I would prefer it.

    Do you have any pics showing how best to seal things (also intake grate and ride plate weren't sealed)?
    IIRC, the factory service manual doesn't mention sealing these parts - which is why I have overlooked them.
    It's odd, because I am certain they were never sealed previously.

    As for RPM, it is turning 8K (whatever the max on the rev counter is), but now that I think back, I am pretty sure it starts this 'rev limiter' feeling, before the revs max out and certainly well before full throttle.

    Also, the veins in the stator housing is it? (the back of the nozzle) are all intact and in good order.

    My current plan is to seal the pump, grate and ride plate and then get it back in the water and see where I am at.

    Reading through these symptoms and thinking about it, it does start to sound more like cavitation, due to drawing air into the pump.

    Thanks again!
    Last edited by SA73FC; 09-02-2014 at 06:39 PM.

  9. #8
    Just to clarify, I sealed the transom to.hull and shoe to hull, after setting the height. when I had the ski back from paint, but I never sealed the transom and shoe to each other.
    Now, they are as good as permanently stuck to the hull.

    If I run sealant along the visible gaps under the hull and inside the tunnel, will this seal the areas sufficiently?

  10. #9

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    you cannot hit the rev limiter while not moving fast without either major cavitation or a spinning prop shaft.. if the motor was not running right it would NOT hit the limiter.

  11. #10
    boudin's Avatar
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    Check the condition of the splines on the pump shaft and intermediate shaft.

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