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Burned up piston, not sure why?


1badws6

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Just got my Shee back together after tearing it down to powdercoat the frame. I put T5's, cool head w 22cc domes, K&N w/o lid while it was apart. Stock carbs, 290 mains, Vito's needle 3rd clip down, stock pilots and 2 turns out. Took it out to the trails this weekend, was running pretty good. Rode about 20 miles and all of a sudden it just loses power. Hop off and check the plugs, one side looks good, light brown, the other is peppered with aluminum. Put my finger or the spark plug hole, hit the kick start and nothing there. Don't understand what happened. Got back to the trailhead and pull the head off and there's a dime sized hole in the left side piston. Why would one side be good and the other burn up? I did notice that there was coolant all over the swingarm and the overflow was empty. Pulled the lower rad hose and it didn't have a whole lot of coolant in it. It was full when I left, not sure what happened. Was it runnin too lean or did it get to hot and then start detonating?

 

The bore looks fine, no scratches or scuffs, so hopefully as easy as a piston swap. Just wanna know what happened to prevent it from happening again! I rode this thing stock for seven years, had it rebuilt a year ago. Had about 5 hours on the rebuild and I burn it up first ride out after modding it. Feel like a dumba$$! Please help me figure it out!

 

Also is there anyone close to the detroit area that knows a lot about Banshees? Would like to have someone give me some pointers with the jetting and possible overheating issue after it fix it.

 

Thanks!

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if i was you, i wouldn't be running mains smaller than 330. i would also be at 27.5 with the pilots. the needles sound fine, as the vito needles are richer anyhow. i think it got hot from being lean, and that's why the coolant came out the overflow. you said that the coolant level was fine before you went riding.

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I have seen fuel lines or filters get clogged and lean out, check that. Also air leaks, stuck float, main clog, any of those cold be a problem. I had a 2001 YZ 125 and i just rebuilt it it had maybe 2 hours on it, a plug check said it was rich on the top end so i figured wen it got all broke in i wood play with the jetting. well about a week later i was going down the road about 1/2 throttle and the thing just died, it lost all compression and everything well i got it home and it had went lean..... you tell me what happened!

 

 

Chevshee

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I wouldn't rule out a leak in the head gasket/o-ring, coolant on the piston will destroy them. As stated need to do a leak down test to ensure there are no air leaks. 290 does sound a bit small for your elevation with your mods, do plug chops to verify your jetting is correct.

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