95 XP Idle, Overheat, and Confusion

[Conboss]

Hey all!

Last year I picked up a sweet 95 XP, got it out on the water and had issues with fuel delivery, ended up cleaning out the carbs and removing an odd filter that was installed by the last guy (Factory filter still in place). Had it on the water all summer, then at the end it ended up overheating and locking up. Ended up rebuilding the top end with new pistons, was able to salvage the jugs and bottom end with no issue. Got it put back together and after having stator problems I was able to get it out on the water and have a blast!! 5 hours of run time later, it decided to overheat again. It's sometimes hard to start on the water now, almost acting flooded but will eventually pull through.

Here is where it gets interesting...

This is after the rebuild. I got it on the water and set the idle to 1400-1500 initially, after running for a while and pulling it onto the trailer and gave it a quick start and found that it was running away!! 4500+rpm and accelerating till I killed it. Super bizarre. Didn't think much of it, thought it just really wanted the water.

Now to the 5 hour mark... Overheated and died on the water, got a tow into the dock. I found that cylinder #1 was hot, #2 was still acceptable. I took it home for the night and did some checks, condition of plugs, borescoped the cylinders and found that #1 had some pitting on the top of the piston but not enough where I'd call it toast. #2 looked like I just put it together not long ago, as expected! Pulled the cylinder head cover off and didn't see any sort of blockage down in the water passages. Put everything back together (Also replaced the wear ring at this time as it was just about done) and took it down to the lake for another spin. Got maybe 20 mins out of it before it started overheating yet again.

I guess I'm wondering a couple of things, could this be related to how the carbs are tuned at the moment? Considering my crazy high dry idle I'm curious, but not convinced. To me it seems as if #1 is the only cylinder getting hot. Blockage in the block? I can blow through all of the hoses free and clear so it shouldn't be something hung up in any of the lines. Is there something I might be missing altogether? Any advice is appreciated!

 

[burtshaver2021]

Difficult to remember your whole post but in a nutshell when you first got it, it had fuel delivery issues, and overheated, you rebuilt the top end. After the rebuild it overheated a few times and ran away due to a lean condition, after the first time it seized did you figure out why? Leak down test before you took it apart? You have a lean condition, carb gaskets, fuel system sucking air, crank seals sucking air. Rebuild again, do a leak down test before disassembly and after rebuild. Rebuild the carb and fuel system with a back to OEM kit from OSD marine, set the highs and lows to factory setting and check the clearance on your wear ring to impeller.

 

[mikidymac]

Sounds like you are running really lean. That "pitting" on the top of the piston is detonation and your are running so lean you are destroying the piston.

I don't see anywhere where you serviced the carbs or fuel system.

 

[Conboss]

Difficult to remember your whole post but in a nutshell when you first got it, it had fuel delivery issues, and overheated, you rebuilt the top end. After the rebuild it overheated a few times and ran away due to a lean condition, after the first time it seized did you figure out why? Leak down test before you took it apart? You have a lean condition, carb gaskets, fuel system sucking air, crank seals sucking air. Rebuild again, do a leak down test before disassembly and after rebuild. Rebuild the carb and fuel system with a back to OEM kit from OSD marine, set the highs and lows to factory setting and check the clearance on your wear ring to impeller.

I know I kinda just threw it all out there, sorry about that..

Sounds like you are running really lean. That "pitting" on the top of the piston is detonation and your are running so lean you are destroying the piston.

I don't see anywhere where you serviced the carbs or fuel system.

When I first picked it up I did go through the carbs and the fuel system, I'm now wondering if something backed off after the rebuild for it to start running like this. I'll go through all of the intake side, see if I can find anything. Do you think a vacuum leak will cause it to have starting issues when hot as well? Possible metal expansion?