97 XP check valve failed.

[gp1200x]

After spending a lot of time doing maintenance and service checks on my old 97 XP I was getting ready to fill the new oil injection lines and winterize it with RV anitfreeze. As the injection lines were getting primed by the pump at idle I noticed that the mag cylinder line was filling at a slower rate than the PTO. After they appeared to be primed I turned off the engine and checked the mag line. The oil was very slowly being drawn back up to the pump and emptying the line which was the exact opposite I was expecting if my check valve was leaking.
I pulled the carbs and used a pressure tester on it. At 30 lbs it was still holding air. I used paper clips and carb cleaner and it cleaned up the valve. It now held and then popped at about 2-3 lbs and held a vacuum over 10 lbs. Cleaned the PTO valve too just in case and it tested at about the same values as the MAG valve. This engine ran great the last time I had used it so the oil had to be flowing since I sometimes run wide open for a while. The line plugging must have happened from sitting for 3 years since I was careful when putting in the new oil lines. This engine would have blown if I had left it as is and not looked into the issue.

Now my 99 XPL (rebuilt in 2006) has me worried too since it sat for three years too I was not going to change the oil lines since they are not brittle and no leakage. Not sure if it is even possible to check those valves properly with oil in the lines since there is no writeup for that type of procedure. Checking these valves probably requires pulling the head pipe and carbs just to get down to them. A whole day of work at best.

 

[Venturian1]

I have three 97's here, 2 GTi's and a GSi, with 717cc, maybe different than a xp, I don't know of the check valves you're referring to. On mine, theoil injection pump has a check valve that serves both injection hoses, and when I get air in any oil injection hose, I idle the engine on premix 50:1 and hold the arm of the pump in max position, and watch the smallest hoses for air, and keep on until no air bubbles are visable. It starts smoking excessively at the end, but will clear up eventually.

 

[mikidymac]

I have three 97's here, 2 GTi's and a GSi, with 717cc, maybe different than a xp, I don't know of the check valves you're referring to. On mine, the oil injection pump has a check valve that serves both injection hoses, and when I get air in any oil injection hose, I idle the engine on premix 50:1 and hold the arm of the pump in max position, and watch the smallest hoses for air, and keep on until no air bubbles are visible. It starts smoking excessively at the end, but will clear up eventually.

Yes, 720's are different.

 

[gp1200x]

Tore my 99 XPL exhaust pipes, carbs and reed covers off after testing my check valves and found one would not hold any pressure. Bought two used ones on ebay that tested good and replaced the defective one. Cleaning would not bring the bad one back to life so I epoxied a new one into the reed cover and installed new oil lines. My valves now hold at between 2-3 lbs of pressure and over 5 lbs of vacuum.

Replaced some hoses when I had it all open and easy access and noticed my primer lines were getting sticky. Replaced all the Tygon hose since this stuff doesn't last forever and tends to get either a little stiff or sticky as it ages. I noticed this on my other skis too and replaced all of it. I only use it for my primer lines and acc pump lines and use Napa fuel line hose for gas lines. Rebuilt the starter since it was 20 years old...didn't need too! Brushes still had the same length as the new ones and the armature only needed slight cleaning. Those Mitsuba starters are unreal. Spent a few days getting it all done and had to redo the exhaust twice since I had a bad seal at the clamp....my fault not a perfect fit before tightening. Finally winterized.