After some expert help!
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Okay so I just tried kicking it up and on the third kick I heard a puff of air like a blow off valve letting out pressure but I'm unsure where it came from it sounded like it was somewhere near the carb or air filter
@ricky0115 Probably tried to fire up but failed.
You haven't blown a hole through the piston have you? It does start right?
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A couple of my bikes used to occasionally make that sound when I was kicking them. I'm sure it only happens on an engine that isn't perfectly set up / running little bit lean or little bit rich? Either way the bikes ran okay.
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I'd say piston rings at a guess maybe just a cracked ring would cause issues
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I'd say piston rings at a guess maybe just a cracked ring would cause issues
@andrewj1680 thanks
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@mightyman I've only known 4 strokes to make that sound
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@declan I think it's drawing in way too much air, everything is standard air intake wise. How can I find the piston size I know it's been bored out but I'm unsure of the size
@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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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
@mightyman dt125r puff of air from top end didn't find any matches for me
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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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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!
