951 Engine failure

[xr246]

Hey guys.

I have a seadoo 951 engine in my jet boat. I took it out today everything was going great cruising about 5000rpm and then I lost power. I started to head for the shore and the engine cut out completely. I got the boat home and did a compression test and found 30psi on the front cylinder and 0psi on the back. I removed the head and found some bad detonation.

Any ideas as to what has caused this? motor has been in boat for a number of years now and has been great

Thanks

 

[riffe723]

That one pistons looks pretty bad. Lol and the compression numbers indicate the top end is toast, if those numbers are accurate.

 

[mikidymac]

Running lean from dirty carbs and or fuel system.

 

[Nemisis]

I agree, leaning out of fuel system caused engine failure.

 

[wolftalk]

on my 951, the pulse/pressure hose that goes to the rave valves cracked where it attached to the bottom of the crankcase. I assume that would let in a bunch of air.

 

[jason myers]

I had the same thing happen on my 720(single carb). I rebuilt the carb with genuine mikuni kit and was still having lean issues between 2k-4k. After a lot of troubleshooting, checking fuel pump, removing inline fuel filter and rechecking pop off pressure i realize that i had been neglecting one crucial component each time i took my carb apart. i was not checking my accelerator pump. When i bench tested its functions using a vacuum pump i discovered that the accelerator pump output check valve had failed and was not allowing any fuel to pass through during acceleration. Considering you have a duel carb setup and are running lean on both cylinders it would be worth a check. Your accelerator pump is a common denominator because it supplies both of your carbs. When performing an accelerator pump check when connecting your vacuum pump to the inlet side you should hold a vacuum and should not hold pressure and on the outlet side you should hold pressure but not hold a vacuum.

 

[jhjesse]

Lean burning probably clogged carbs. Rebuild carbs with only genuine Mikuni parts.
Fog the cylinders after every use. Use only good oil

 

[Bobbyg5502]

As an added note, I would switch to premix and ditch the oil pump. The pump isn’t the problem. It’s the location of the oil tank IMO. I rebuilt a 01 XP and planned on using the oil injection. I purged the system when I got it running and noticed air bubbles in the lines. One look at that and quickly changed my mind. Runs happy ever since. Good piece of mind too.

 

[mikidymac]

As an added note, I would switch to premix and ditch the oil pump. The pump isn’t the problem. It’s the location of the oil tank IMO. I rebuilt a 01 XP and planned on using the oil injection. I purged the system when I got it running and noticed air bubbles in the lines. One look at that and quickly changed my mind. Runs happy ever since. Good piece of mind too.

Actually it isn't and issue on these. Seadoo pumps are extremely reliable and will save you a lot of oil over premixing.
The only thing I have seen go bad on them is a plugged filter from improper maintenance or the little 3/32" oil lines from the pump to the intake breaking from no maintenance. Change the oil filter every couple of years and the oil lines every 5-10 years and they will be fine.

If you have air in the lines you have not purged it enough or correctly. My 2001 XP doesn't have any air bubbles.

 

[riffe723]

Actually it isn't and issue on these. Seadoo pumps are extremely reliable and will save you a lot of oil over premixing.
The only thing I have seen go bad on them is a plugged filter from improper maintenance or the little 3/32" oil lines from the pump to the intake breaking from no maintenance. Change the oil filter every couple of years and the oil lines every 5-10 years and they will be fine.

If you have air in the lines you have not purged it enough or correctly. My 2001 XP doesn't have any air bubbles.

100%. I hate when guys recommend premix on these. Save SO much more oil and the oil injection, like you said, is really reliable.

 

[Bobbyg5502]

Maybe the lines to the intake were cracked or like you said, I didn’t purge it enough or correctly. Once I saw that though, I didn’t want to take any chances. I agree that the oil injection system is a great system. My 720 system is flawless to this day.

 

[xr246]

So I have finally got around pulling apart my 951 engine. I have found the accelerator pump line has rubbed thru.

Guessing this has caused my problem and made my engine run lean? front cylinder has definitely run a lot leaner than the rear. as I don't think the rear ran lean at all. I think it failed when the front cylinder lost compresson and overloaded the rear cylinder

Crank now has very noisey main bearings and the one jug and a large grove and the engine is already at 1mm oversized

 

[jason myers]

I'm glad you found a culprit hopefully that is the only issue. I haven't had problems with mine since I found my stuck accelerator pump check valve. Maybe you will luck out and itll be one of your outside main bearings going bad for an easy and cheap replacement. I have found cylinders for really cheap too on ebay.