Background......Engine is a JM781 dual 38's, prepped by Blue some years ago. It has run flawlessly in both surf and bouy chasing.. We did a river dash around 50 miles 2 weeks ago and every now again we would go WFO for a few minutes and then back off a bit ....just before the end my ski died at WFO and took a few attempts to get it started again...motor initially cranked very slowly like the battery was dead...but battery was fully charged ....At the end I did a few hard short bursts around a few trees on the flooded river and all seemed fine.....However, I thought to do a compression test to be safe....... front was 160 rear was 175....that hurt. Overheating was not a factor as the overboard pisser from the head has a solid stream to the point I think the ski should run a bit hotter.
I will send a few pics of what I saw when I took the ADA head off...Damage is clear on the front cylinder, looks minorish.. Rear cylinder has no visible damage....Based on what I saw first it appeared to me as though the front dome o ring could have ruptured and leaked water into the front cylinder, causing fuel to be washed away from the cylinder sides and that caused the seizure. However, once I removed the cylinder and inspected the pistons I am now clueless. So anyone have any theories....ski runs extremely well at all speeds from idle all the way to WFO..(just never had it run hard for so long GPS clocked it at 49 mph) ....I will obviously check the carbs and do a complete teardown but any help
And below pics with cylinder removed
So the front piston has one ring jammed up tightly...and the piston damage is extensive...It's the rear piston that has me completely stumped....the rings are still flexible and the damage looks worse than it feels...my finger nail can't feel any grooves , but clearly something else happened...maybe just way too lean on WFO is the simple answer...jet up HS jet to next size up maybe ?...timing is stock and using MSD enhancer. JM coil.
I will send a few pics of what I saw when I took the ADA head off...Damage is clear on the front cylinder, looks minorish.. Rear cylinder has no visible damage....Based on what I saw first it appeared to me as though the front dome o ring could have ruptured and leaked water into the front cylinder, causing fuel to be washed away from the cylinder sides and that caused the seizure. However, once I removed the cylinder and inspected the pistons I am now clueless. So anyone have any theories....ski runs extremely well at all speeds from idle all the way to WFO..(just never had it run hard for so long GPS clocked it at 49 mph) ....I will obviously check the carbs and do a complete teardown but any help
And below pics with cylinder removed
So the front piston has one ring jammed up tightly...and the piston damage is extensive...It's the rear piston that has me completely stumped....the rings are still flexible and the damage looks worse than it feels...my finger nail can't feel any grooves , but clearly something else happened...maybe just way too lean on WFO is the simple answer...jet up HS jet to next size up maybe ?...timing is stock and using MSD enhancer. JM coil.
