CAVITATION ISSUE 1999 GP 800x - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
 
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post #1 of 6 (permalink) Old 08-13-2019, 12:00 PM Thread Starter
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CAVITATION ISSUE 1999 GP 800x

Hello I have a 1999 Yamaha GP800x that is having top speed issues. It reaches 7100 RPM with no problem but will not exceed 35mph. The clearance between the impeller and housing is .533mm (0.021 in) which seems to be within spec. I am not sure what the issue could be. I Think it is Cavitation but I don't know where from. The ski has a Shred master ride plate and a pro-tec grate, those are the only aftermarket parts.

Thanks in advance for all the help!!
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post #2 of 6 (permalink) Old 08-13-2019, 03:00 PM
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Hello I have a 1999 Yamaha GP800x that is having top speed issues. It reaches 7100 RPM with no problem but will not exceed 35mph. The clearance between the impeller and housing is .533mm (0.021 in) which seems to be within spec. I am not sure what the issue could be. I Think it is Cavitation but I don't know where from. The ski has a Shred master ride plate and a pro-tec grate, those are the only aftermarket parts.

Thanks in advance for all the help!![IMG class=inlineimg]https://www.pwcforum.com/images/PWCforum_2016/smilies/tango_face_smile.png[/IMG]
Do you have a plastic or metal wear ring?
If your clearance is .021" your near the outside limit. .008/.024 is the inside/outside clearance limits for that pump. Above around .018 your going to start having cavitation problems.
You could also have a shaft seal or pump housing leaking air. The shaft seal usually comes with a water leak into the ski as well.
If when trying to excelate quickly the rpms go up and speed doesn't. That definitely is cavitation.
then I'd say you it's time to rebuild your pump. I'd use a solas Concord and rebuild the pump brgs at the same time. If you have a plastic wear ring I'd replace with a good used original from eBay. The plastic ones need frequent replacement and cause issues.
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post #3 of 6 (permalink) Old 08-13-2019, 08:04 PM Thread Starter
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Thanks! It does have a metal wear ring. The Duct housing is also in very rough shape I just took it all apart today. Will the Duct housing cause cavitation as well? I should ask what is the purpose of the duct housing? Thanks for the help!
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post #4 of 6 (permalink) Old 08-13-2019, 09:19 PM
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Thanks! It does have a metal wear ring. The Duct housing is also in very rough shape I just took it all apart today. Will the Duct housing cause cavitation as well? I should ask what is the purpose of the duct housing? Thanks for the help!
I suppose it could. Especially if it has a crack that it could draw air into the pump. The condition of the Impeller itself can cause it if it's nicked, bent, or damaged.
The duct just creates a path for the water to feed the pump.
Can you post a pic of it and damage?

Last edited by Dave in DE; 08-13-2019 at 09:25 PM.
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post #5 of 6 (permalink) Old Today, 12:23 PM Thread Starter
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I solved the problem! The previous owner ground down the leading edge of the impeller making it into a rounded shape instead of a straight edge. Not sure why he would have done that but got a new impeller and it runs perfect.
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post #6 of 6 (permalink) Old Today, 01:44 PM
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I solved the problem! The previous owner ground down the leading edge of the impeller making it into a rounded shape instead of a straight edge. Not sure why he would have done that but got a new impeller and it runs perfect.
Glad to here your on the water again.
Just curious, what was the clearance when you put it back together?
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