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Discussion Starter #1
I just went thru the painful process of replacing the engine mounts on my 2005 FX Cruiser HO. During the process I also changed the spark plugs and impeller housing. The engine runs fine and ski runs good but on take off, the ski seems to be cavitating until up to speed. I used to have a top speed of around 63 mph but now only around 59 mph. Since the housing is new and the impeller seems in good shape, why the loss of thrust? Could the cavitation be due to not applying enough yamaha silicon when installing the housing, impeller, and nozzle?

Thanks in advance!

George
 

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From your description you have a cavitation issue. If there is nothing caught in the shoe or impeller visually. then it must be air infiltration or high impeller gap clearance.
After replacing the impeller wear ring. what was the impeller to ring clearance? .018" is max clearance. You replaced the wear ring. Most times although the impeller looks good, It is usually the impeller that is worn. If you are close to .018" then replace impeller. I also suggest a pump shoe seal kit from Riva Racing. Then seal the shoe in with a little silicone caulk. Follow either the green or red layout in the pics below. Use Which ever will give you a good seal. Do not let silicone ooze into pump tunnel. Wipe clean if if does.
The pump seal kit fills all the open air gaps in the shoe. use small dabs of silicone to glue the pieces of seal kit into shoe. Then install shoe in ski.

Good luck, Ride safe.
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Discussion Starter #3
Dave, thanks for the quick reply and information. I took everything off from behind the shoe but didn't remove the shoe. On my ski, there is supposed to be a rubber seal between the grate and the shoe. I don't recall seeing it, and am hoping that is the problem. The ski is sitting on a floating lift right now so I can't check anything till I get the ski out of the water. I will check all of the spots you mentioned once its in my drive way again. There are gaps between the shoe, housing, impeller housing, and nozzle that are supposed to get sealant between them on installation. Any idea how much sealant I should use upon reinstalation? I used the yamaha sealant very sparingly the last time as you probably know, they can be very difficult to remove due to the sealant. I'll let you know what I find later this week.

Thanks again!

George
 

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George,
I don't ever use any sealants on my pumps sections. Only on the shoe. Your model does have a foam rubber seal across the back edge of the shoe. If this broke up and came out when you removed the ride plate. It could cause an air leak. Again I would use the seal kit and silicone caulk to seal this area back up. In stead of replacing that foam seal.
 

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Discussion Starter #5
Dave, I removed the entire drive this evening. Good news is the clearance between impeller and housing was around 0.014" so I should be in good shape there. The rubber seal was still in place on the shoe with some sort of sealant on it but there was a gap between the shoe and hull. I am hoping this is my problem. What exactly do you use as far a silicone caulk to seal up the shoe to the ski?

Thanks again!

George
 

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I just get a good grade of silicone adhesive caulk from ace hardware, Lowe's, or home depot. I usually use white as that's my hull color but clear will work as well.
Really any quality 100% silicone caulk will be fine. Just look for it to say superior adhesive properties.

The clearance being .014 puts you on the lower side of Yamaha spec's. Most that I just replaced the impeller on got me to around .008/.010.
 

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Discussion Starter #7
Dave, had to go with the red version of caulk. There is a gap between the shoe and hull that the green version of caulk wouldn't have filled. I am hoping that as long as the red version is complete, the gap won't matter. Riva didn't have a seal kit for this ski. Jet ski hopefully will go back in the water this evening. Will let you know how it works.

Thanks, George
 
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