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Engine Slippage / no thrust / high rpms

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buddygreg

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New to Forum..Hope someone can help...Never owned a Jet boat, boat a 2000 sea doo challenger 14 ft with twin engines..Took it out. Both engines start great/ when taking off out of the hole the left engine rpms rev high but I get no thrust to take off.(like slippage or something) any ideas of what i can do.
Thanks !
 
thanks for the quick reply. I am new to this and I love it....before I registered I just read that article you just sent my..very nice...but the cavitation you are talking about, is that related to my problem? I should look to see if that engine has a worn ring?
 
Since you are new, I will try to describe why it is acting like that. To really understand how these boats work might solve a lot of your questions. The basic concept of jet boats is jet propulsion. Normal prop boats use an external prop to push the boat along. Jet boats use an internal impeller. Think of it like a big fan blade. It sucks water up through the bottom of the boat and pushes it out the back through a smaller opening, creating force and moving the boat. That is the basic concept. When there is a restriction to the water flow, this thrust is greatly reduced. If there is a leak anywhere on the outlet side of the impeller, you get no thrust. This loss of thrust is called cavitation.

1. The intake on the bottom of the boat can become clogged up with weeds, sticks, and other debris. When this happens, the impeller no longer has water coming through it and therefore you have no thrust to move. If something has been sucked up in the past, it has probably damaged the wear ring. The ring is there to give a little and prevent the impeller from just being tore up.

2. It should be very fast to get up on a plane. Faster than a lot of other boats. If it feels like something slipping, you may be experiencing cavitation. Could be something as simple as needing a new wear ring. A wear ring is like a gasket that incases the impeller.

Soooo...That is more than likely your problem.
 
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That's classic cavitation.

Since it's an older boat, and new to you... I would buy 2 new carbon ring seals, and 2 new wear rings, and freshen up your drive system.

The carbon ring is inside the boat, and it seals the drive shaft. (keeps water from coming in) BUT... when they start to leak... they allow air into the pump. And as soon air gets in there... you loose thrust.


The wear ring is a sacrificial plastic/fiberglass/rubber ring around the impeller. When they wear out... they also cause cavitation. I just posted a "How to" on changing the impeller. (top of this section as a sticky)
 
thanks so much for you replies. i will check into both of these..first time i took it out it ran great. Then pulled a tube and ran great. next time i went to take off the Rpm went way up, but no thrust..Seems odd that all of a sudden, but I beleve that could have happen that fast.
 
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