After some expert help!
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I'd say piston rings at a guess maybe just a cracked ring would cause issues
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@andrewj1680 thanks
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@ricky0115 markings on top of the piston should give you the size or measure the bore with calipers, either way it's the head off, not a big deal. Personally think your problem lies elsewhere but expect to be proved wrong, see what the garage says, hopefully something simple. Good luck
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Just had a quick Google and first couple of results suggest worn rings / not correctly sized piston, which makes perfect sense because the sound will be the air squeezing through the ring seal when compression is happening.
I suppose this means my bikes could have been a bit down on power not having a correctly sized piston
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I've had this before on a high mileage DT125R and due to being poor I left it with dire consequences. Basically the piston tried to make its way out via the exhaust port. I went from a standard bore to 2.00mm oversize in one go which made me cry when I realised.
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It's not seized, managed to get it in the garage there's a hole in the piston and some scrapes on the barrel, they advised a full rebuild so I've gone with it. At least it will be done properly and will be under parts warranty!
There goes my new fat bars & koso digital instruments till next month
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@ricky0115 And I refer you to my initial prognosis of the problem...
Who have you taken it to to rebuild it?
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@ricky0115 Yeah nice. I only ask because these engines MUST (and I can't stress that enough) be built using either genuine or Athena head gasket.
If they use anything else then it absolutely will blow the head gasket.
But if they're a genuine Yamaha Dealer then they should be using genuine gasket.
What piston are you going for?
A hole being burnt through the piston is a big sign of the bike being incorrectly jetted.
You've effective welded through the piston.
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I have gone for the wossner? It's was about £70, it's a genuine Yamaha gasket, so the bore will be standard again I guess?
I have only had the bike about 2 weeks and I'm new to 2 strokes so I wouldn't have been aware of any jetting issues so I'll make sure it's up to scratch when I get it back! I know it has a 240 main jet but that's about it.
Thanks for your help!
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@ricky0115 Yeah nice. I read on PJME that Wossner were having their parts made in China, but I have Wossners in mine so it's fine.
Could be the wrong plug bud, too hot.
I would be very inclined to getting a new plug for it as well.
It might not be standard size if you have damaged the bore, it'll require a rebore.
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Fair enough, it's the plug recommended in the Haynes manual NGK BR9ES, not sure if the gap was wrong maybe? They do an iridium plug also if they're any better?
Any tips on running it in? Is there any way to limit the throttle as my rpm counter doesn't work.
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@ricky0115 Shouldn't worry about revs, it's more load if anything.
Just bed the engine in gently or 100 miles. And vary the throttle after that.
It's all about trying not to glaze the rings and cylinder walls.
