What is the minimum compression a 787 will run on?

[Turbonator]

I just bought a 1997 SPX (basically a 96 XP) and when I saw it it fired right up, and ran nice and smooth. Then, when I got home and put it in the water it also started right up but it would never really go any faster than just a bit past idle speed. Had this sound where every now and then it would do a loud POP POP sound like it was about to come back to life and go full send, but it never did. So my line of thinking is the carbs sat for too long and need to be rebuilt, it's probably typical hesitation and stalling from these old jet skis after they have sat still for a season or two and the carbs have gummed up. However, just before buying the carb rebuild kits, I decided to buy a compression tester and check where it was at. The MAG cylinder has 150 PSI and the PTO cylinder has 90 PSI of compression. Well there is my problem. Low compression on PTO cylinder.

What do I do now? I never had to deal with something like this on a 2 stroke engine before, and I'm new to the seadoo world.

 

[etemplet]

Do the top end.

 

[Turbonator]

Do the top end.

I that pretty much guaranteed to be the problem? I mean even if not, I still have to because of the compression, however could there be a deeper root to the problem?

I am about to order a top end rebuild and a carb rebuild, the fuel lines look OK they are not the original green ones, they have been replaced with some kind of hard plastic see through lines. Also, the choke has been replaced with a fuel primer, and the primer taps in to the fuel return line. Also, the stock air box has been replaced with some kind of billet aluminium "cold air intake" filter. Can't tell the logo, but it might be RIVA Racing.

 

[etemplet]

Well , no one can guarantee all that aftermarket work is correct. I think it is prudent to assume everything else is correct and do the "top end." The ski is not going to run very well if at all with 90psi on one cylinder. Fix one thing at a time and gauge improvement. You know the compression is bad... you'll check the rave valves during the top end work so you will be well on your way to solving any other issues. What you are doing is what I call, "eliminating what is NOT the problem. " Good Luck !!