CavScout

I noticed at the end of the summer that one of my waverunners lost a little on the top end speed (approx 42 mph from 52 mph). I finally conducted a Compression test and got 150 psi for the front cylinder and 120 psi for the back cylinder. I did spray some fogging oil in the rear sparkplug and rechecked and it raised the compression about 10 psi to 130 psi.

From my understanding, normal compression for these skis is around 120 psi. I also checked my other twin ski and she showed 120 psi for each cylinder. If this is true, what causes compression to be higher in a cylinder?

Both my skis have always been extremely hard to start since I bought them a few years ago so I know I need to rebuild the carbs. Is it possible the loss of speed and compression differences is from the carbs only? If so, would the recommendation be to just rebuild the carbs and then see if that fixes everything or should I check the cylinders.

If I check the cylinders, is it possible to pull the cylinder head without removing the entire engine unit. According to the service manual, it shows pulling the engine unit, but I am afraid of going in too deep as I have never done this before.

Thanks for any help.

CavScout

Although I never received any replies on my post, I thought I would give an update for anyone having the same issues.

I have slowly started breaking down my ski and have now completely removed the engine. I am a shade tree mechanic, but it has actually been pretty straightforward using the Service Manual. For the 2004 XLT 800, you can remove the Cylinder Head without removing the engine, but that is as far as you can go. In order to really examine everything, you must remove the Exhaust Manifold which requires the removel of the engine. Although it was a little heavy, I was able to remove it by myself with no other assistance or engine lift. If there were 2 adults then it would be a breeze. Once you remove the engine then you can access the 2 YPVS's and the actual Cylinders so you can see the Pistons.

Both of my pistons looked great; however, I found the problem was one of the Valves from the YPVS had broken in half. It just so happened that it corresponded with the cylinder that had a Compression reading of 150 psi. The broken valve prevented it from rotating back and forth into the cylinder which was the cause for the loss of power, or at least I hope.

If I encounter anything else I will update as needed. Hope this helps someone else.