Other Engine sputtering when warm

[Rowley286]

I've been battling this problem for 2 weeks now. Runs great when its cold for a few minutes then I get a horrible sputtering and it feels like im riding a js300, no power and sounds horrible. I figured it was a jetting problem so I rejetted my carbs.. nothing. Checked everywhere for an exhaust leak and came up with nothing. Cut back my plug wires and new boots.. nothing. Removed my engine temp. sensor and that didn't do it either. I've been running this motor for 3 months and have had zero problems until now.

Would a very small exhaust leak cause this? Maybe I should try replacing my exhaust manifold gasket? Even though it's only a few months old.

 

[964Chris]

Check for a blown head gasket/ o ring. Do a compression check.

 

[Rowley286]

I pulled the head off and the pistons are black, def. running too lean, I thought the jetting was ok tho and the plugs look good. The gasket looks good, O-rings ehhh not so good. Overheating? I did just replace all my cooling and fuel lines yesterday just for the heck of it and no luck today. Here's a couple pics..

 

[tor*p*do]

way lean piston wash, fatten it up
that may be the source of overheating as well

 

[Rowley286]

New o-rings will be here tomorrow and i'll check compression, hoping that was the problem. Should i try a different plug? I've always ran ngk b8hs with no problems.

 

[964Chris]

what head are you running? most aftermarket heads require ES (extended reach plugs)

 

[swapmeet]

Never knew thats what ES meant. Learn something new every day.

 

[Rowley286]

Ok took a couple pictures, ive been running b7hs which is the used plug on the right. The other new plug on the left is a br7es. Riva head 35cc domes.

 

[tor*p*do]

yup, you need to run ES plugs.
but that would not make the combustion chamber lean.
run it with the hood off to see if still sputters- you can do this on the trailer if you local boat ramp is OK with it
to diagnose exhaust leak

 

[Rowley286]

Swapped out the plugs, ran all new cooling and fuel lines, fresh o-rings, all new gaskets from jetmaniac. I Was only able to ride for a few minutes before dark last night but it seemed to be running good again. Still need to play with the carbs a bit to get it perfect, happy to be back on the water.

 

[NVJAY775]

Is the fuel tank venting properly? Sounds like a faulty breather to me. Find a drill bit to drill it out, blow it out with compressed air and re install it. No mo problemo.

When the one way valve fails inside the breather, the ski will run fine for a bit, then the vent basically won't let air in and make the carbs lean out, due the the tank trying to pull the fuel back out of the carbs. Kind of weird, but semi common.