1999 Seadoo GTX Limited - Good PSI?

[Rob451988]

bought this GTX 3-4 years ago. 951 motor. I believe I'm the 2nd owner. pervious owners were older and said they didn't beat up on it. As far as I know the engine has not been rebuilt or replaced. 293.8 hours on the info. are these good for compression? I saw 130-150 is new, also saw this motor is lower compression so 120 might be fine?

 

[tobytd]

120 is fine
130 brand new

 

[Rob451988]

these are warm readings, the originals were cold readings

 

[tobytd]

How does it run?

 

[offgrididaho]

300hrs means it needs a complete rebuild. Mine at 225hrs was needing a rebuild and is being rebuilt. The cyl had a ridge at the top, the end crankshaft seals were shot, the raves were leaking, the carbs needed rebuilding, and the pump need a bearing. So to keep running that you risk blowing the motor. Also 150-155 is new, 120 is low and needs rebuilt.

 

[Rob451988]

It idles just fine. It bogs down just a little bit when trying to plane but once it actually planes it runs great. 5000-5500 RPM about 30-35 mph. I try to keep it under that 5500 RPM mark because anything over 6K seems to blow the short exhaust hose/ connector between the exhaust manifold and the water box.

 

[Rob451988]

Just today

 

[etemplet]

300hrs means it needs a complete rebuild. Mine at 225hrs was needing a rebuild and is being rebuilt. The cyl had a ridge at the top, the end crankshaft seals were shot, the raves were leaking, the carbs needed rebuilding, and the pump need a bearing. So to keep running that you risk blowing the motor. Also 150-155 is new, 120 is low and needs rebuilt.

I've done a few top ends on the 951 and replaced a few engines. I don't recall ever doing a compression test on any of those. LOL I read people say that 135psi is new compression but I wouldn't know. First thing I check on a ski is compression though for troubleshooting purposes. I did test a 951 DI that had 120 PSI and Tom at SES told me that was about midpoint for the engine. I did a top end anyway. Once compression starts to drop off there is damage, scouring and ring issues. It's leaking and it doesn't take long to go from bad to worse. I see 717 and 787s when the compression is around 130psi there is some visible damage. I had 1/4 of the top ring missing on a piston and still had 130psi on that cylinder.

If owners would take care of these skis the engines would last longer for sure. They ride them hard and put them away wet.

 

[etemplet]

It idles just fine. It bogs down just a little bit when trying to plane but once it actually planes it runs great. 5000-5500 RPM about 30-35 mph. I try to keep it under that 5500 RPM mark because anything over 6K seems to blow the short exhaust hose/ connector between the exhaust manifold and the water box.

View attachment 69401

I'd check the exhaust system for a bad hose or at least make sure you are getting good flow. Are you using the screw type Hose clamps?

 

[offgrididaho]

I've done a few top ends on the 951 and replaced a few engines. I don't recall ever doing a compression test on any of those. LOL I read people say that 135psi is new compression but I wouldn't know. First thing I check on a ski is compression though for troubleshooting purposes. I did test a 951 DI that had 120 PSI and Tom at SES told me that was about midpoint for the engine. I did a top end anyway. Once compression starts to drop off there is damage, scouring and ring issues. It's leaking and it doesn't take long to go from bad to worse. I see 717 and 787s when the compression is around 130psi there is some visible damage. I had 1/4 of the top ring missing on a piston and still had 130psi on that cylinder.

If owners would take care of these skis the engines would last longer for sure. They ride them hard and put them away wet.

Yeah, the thing people dont get is ----> Compression=Horse Power. Low C= low HP, High C = High HP.
We used to deck our head and modify squish band on old first gen skis to boost compression and add HP. Then we ran Avgas, dried our pipes up a bit and they ran great. Not sure how much hp we gained but the skis were 30% faster and snappier. Night and day difference.

 

[etemplet]

Yeah, the thing people dont get is ----> Compression=Horse Power. Low C= low HP, High C = High HP.
We used to deck our head and modify squish band on old first gen skis to boost compression and add HP. Then we ran Avgas, dried our pipes up a bit and they ran great. Not sure how much hp we gained but the skis were 30% faster and snappier. Night and day difference.

That's cool !! I thought about decking the cylinders on one of the skis. I have a lathe and sometimes bore my own cylinders. Easy peasy to deck when you are set up for boring.