SBT engine help

[factorysupercharged]

I recently purchased a 95 Seadoo XP with the 720 motor. After replacing fuel lines, filters, carb filters, wear ring, etc. I finally got the ski running ok from idle to 3/4 throttle. Above 3/4 throttle engine would act like it was cutting out so I played around on it for about an hour then on a straight run engine died out of nowhere. Long swim to shore long walk to boat slip got it home found 125 compression on pto side and 0 on mag side. Pulled heads found broken piston as expected. Pulled pistons found 100 scribed on top of pistons and SBT under skirts. Can this motor be sleeved with new pistons or is it bored as far as it will go?

[Grumpy Old Guy]

You are at max overbore,you need to get a used set of cyls & have them bored to fit OR

SBT has a topend kit that will come with pistons already fitted.

Go to their website & look around www.sbtontheweb.com

It also sounds like the carbs were the culprit of your running issue that led to the failure. Did you rebuild the carbs ??

[factorysupercharged]

Didn’t rebuild the carbs just cleaned all the gunk and the little black internal filters. Pistons are both dark and oily so doesn’t that mean they were running rich? Spark plugs the same.

[Grumpy Old Guy]

You should rebuild the carbs with new rebuild kits perferably Mikuni kits.

I was wrong in that SBT does sell 1.50 pistons....https://www.shopsbt.com/jetski/Sea-D...i-1995-03.html

As far as pistons being dark does not always mean rich.

[hafweigthr]

As a side note -You must also check to make sure the oil injection pump is set right and working as well if you have not converted to premix.

[factorysupercharged]

I think that’s actually what happened when I was replacing the fuel lines I noticed the oil lines were brittle so I changed them also but I didn’t know you had to bleed air from lines so I think I just starved the engine on oil. Only thing is it ran straight for at least an hour before it went boom