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My son went to start the ski and it made a huge bang. (similar to an M-80 if you know what I mean)
I looked under the hood, and after the smoke cleared I saw a butt load of fiberglass chunks everywhere. I believe what exploded was the water lock box. (a fiberglass box, about the size of a big shoe box, located under the carberator.

Can anybody tell me;

A. What would have caused this? (the ski ran great all weekend til this happened) is this a common problem with these skis?

B. Can this be replaced without pulling the engine? (I can get the part for about $150.)

C. Can it be replaced by a backyard mechanic (me) or do you need special tools/hoist/ etc. and lots of prior jetski repair knowledge?
 

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I am not sure what the "water lock box" you are referring to is?:dunno: Perhaps the waterbox, but that is in the rear of the hull and is basically a muffler like in your car but filled with water.

You might have blown a hole through piston and need a whole engine rebuild. Can you post a picture of your engine compartment?
 

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A. Unburnt fuel builds up in the exhaust system and ignites when it gets hot enough = BANG!
B. Don't know on your ski since I don't have a service manual. If you can remove the box without taking the engine out then it should be possible.
C. Yes. Even if you have to remove the engine, these 2 strokes are fairly light, and can be pulled without a hoist in most cases, but you will need your son to help. Look at SBTs website for an engine removal/installation guide. http://www.shopsbt.com/

Does it look something like this?: http://www.pwctoday.com/attachments/f14/204291d1260995008-701-boom-what-have-i-done-help-waterbox-002.jpg

Now here is the bad news. When this happens it is usually because one cylinder is going bad, and letting raw unburnt fuel pass into the exhaust system. So, you may have a much larger problem than the blown water box. It may be time for an engine rebuild. Check your compression as a first step. Best case senerio would be a fouled spark plug or loose wire preventing one plug from firing, but you may want to pull the top off the engine and take a look at the pistons just to be safe if the compression numbers are low on one cylinder.
 
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