95 xp 720cc

[rjtx667]

I am new to jet skis, but have been looking around and reading the manual. I am still lost on these 2 stroke engines and rotary value stuff.

Engine ran when I got it, but any time you put it in water it seems it would bog down and die. Then be hard to restart.

figured it was a carb issue, so I rebuilt the carbs. Cleaned parts and found clogged pilot jets and such. The Pop off pressure was also wrong.


Took a while to get it all dialed in, but it started and seemed to be doing better. once started it would stop/ start just fine out of water on the hose adapter (stopping water flow when engine was off). Took it to the lake and got it to start one time and idled a bit then died.

Tested the battery, and it was swelling after the charge so I bought a new battery and rented a compression tester.

I followed the instructions on here:

1) remove plug boots and put on grounding post
2) remove both spark plugs.
3) install compression tester in 1 cylinder at a time
4) with WOT press start button and keep going until you see max PSI
5) repeat 3 times
6) move tester to other cylinder and repeat 4 & 5

I got 60 PSI in the front (MAG) and 28 in the rear.

I know thats extremely low, so my questions are:

1) Besides internal damage is there anything to cause low compression? IE rotary valve timing off etc
2) is it possible for these things to run on such low compression?


the first time I took it to the lake it had issues idling (before the carb rebuild) but I got it out there and at higher RPMs it ran great and would hit WOT and while no speedo I have little doubt it did 40-45 MPH. this does not seem like it would be possible with the low compression I just took?

thanks for any and all help.

 

[AdamXP800]

Sounds like you have some serious damage if those readings are correct



96 XP800!
Keep the 2 strokes alive!

 

[AdamXP800]

I would try another gauge



96 XP800!
Keep the 2 strokes alive!

 

[rjtx667]

Its a rental tool from O'Reilly. I will return it tomorrow and rent one from Auto Zone.

I really hope the readings are wrong. if not I guess I get to learn how to rebuild a sea doo.

 

[benjilafouine]

Yes, please do. And by the way, there are these cam kits that allow you to see the inside of a cylinder. This usually tells you right away if the engine is toast. Not sure you can rent one though. When there is no water resistance (outside of water), a half broken engine might still start (read low compression) but when you put it in the water, it often dies. Been there, done that.

Benji.

 

[Austrian Rotax]

what probly happened was the last time you hit WOT with it you were lean and burned them pistons up. The lesson here is never operate a 2-stroke sea doo anywhere near WOT without ensuring the fuel system is up for the job. you did the right thing by rebuilding the carbs but I think it is too late I hate to say but rarely are compression gauges that far off, im not saying its impossible considering all the Chinese junk we get these days but more commonly they are 15-20psi off at most for the avg. $30 gauge. good luck

 

[jts32]

Well, hate to say it, but even if the gauge you are using is off, the difference between the two cylinders is excessive at 32psi. Think you're looking at a top end rebuild at a minimum.

 

[rjtx667]

hmm I did not think about the bore scope.. I have one of those laying around from working on my Cummins. Sadly my camera is cheap and the stroke does not seem long enough to let me see anything. I guess I could always remove the head and just see what it looks like. Worst case (or best I guess) is it looks good and I get a new gasket and put it back together.

I did not keep it at WOT for long, just accelerating but yes that could have done the damage.

Going on the theory that the gauge "is not that far off" and the engine has low compression.... what is the next step?

Could I get away with just a top end rebuild or do I need to rebuild the whole thing?

If I have to rebuild it, how hard are they? or is it worth it to just pay the $$ and get one rebuilt?

I guess another question which would be a lot of personal preference... is it worth putting $$ into these older jet skis? I have about $800 in this one with the trailer. It has signs of abuse, and the multifunction gauge does not work at all.. not sure why.

Signs of abuse means I see where the engine was either over heated or something as there is lots of melted/ heat damaged stuff. I did not see this until after I bought it. Of course it had also sat for a while but I was told it was in good working order yada yada.

Even so, if you figure the trailer is worth 300 or so... thats not a bad price. rebuild an engine and it still seems reasonable... and even if its old, I at least know that the engine is good.

 

[benjilafouine]

That is a good question. Do you intend to do all the work by yourself? If yes, then you could fix it without spending too much. If you do not have the tools and/or the knowledge, I would really question myself. If the Sea-Doo is very clean and the hull is pristine with everything else working (but from what you are saying, it is not the case), it might be worth it.

But if you intend to pay someone to have it done, you will find out that the price is very high. I had mine fixed and if I had to do it again, I think I would have done it differently (like not fixing it).

Benji.

 

[rjtx667]

I have a lot of tools, and do all my own automotive work. Rebuild engines, done top ends on trucks etc. I don't usually get too scared, and yeah doing it yourself saves money.

I have seen people talk about http://www.fullboreonline.com where you can send off the cylinders to get worked on and cleaned up, then just install them when they come back. Are they a good company with good products?

if I do go into this and rebuild, what do I need to look for to know if I can just do a top end or if I need to do a full rebuild?

Thanks for the help.

 

[rjtx667]

So got into it this afternoon. Yeah something bad happened to the mag cylinder. The rear one looks to have a few hot spots but nothing like the front.


That gets me back to my other question... how do you figure out if you need a total rebuild or just a top end rebuild?

 

[benjilafouine]

Basically, if any debris fell into the crank, top end rebuild is useless. You have to open the whole engine, no choice.

Benji.