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Post Info TOPIC: dt125r sudden very weird issue


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RE: dt125r sudden very weird issue
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when im looking at the pics really careful it looks as though the ringss are embedded really deep and the first ring isnt there take a really good look


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by the way my barrel was on its first rebore just checked with the geezer that did the rebore it was 56.4mm which is standard apparently


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Ok. I need some help on this one but my instincts tell me:

Too rich air/fuel mixture and not enough oil.

Once again I need some reassurance on this one.

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she smokes hard on start up?



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Yeah they all do.

It's probably the sht oil you're using.

If you're going to ramp the tits off your DT then you really need high grade oil.

My bike was nicked and ramped for 24 hours and was in better condition than that.

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bob marley hard


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what oil should i go for ul get it tmoz and where should i go for a rebore etcas im not going back to those ****ys thanks


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NORFE Recommends pmje.

NORFE is very knowledgable.

Personally I stick to standard bore size but that would cost a lot of money. I always go for mitaka piston kits. Very good.

The oil I use is called silkolene comp 2 plus. I buy it from a yammer dealer. It's about 22 a bottle. Expensive but I trust it completely.

Castrol racing oil is about half the price and a lot of people recommend it.

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thanks.for all of your help if norfe is around can you thank him to



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Get the top end off and get some pics..

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1998 Yamaha DT 125 R - SOLD



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looks like its got to hot ie lack of oil. looks like it hasnt been worn in propply too. need resleeving or a rebore but dont forget if u rebore u may need to shave the power valve

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cheers everyone the cylinder is still as it was when i ahd it done which is an odd thing :s .i thought the bike was running to rich. just ordered a wiseco piston ,air filter ,plug,clutch lever,brake lever i love my dt shes a tough old girl.

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Personally I wouldn't have wiesco piston.

I would stick to mitaka. Nothing wrong with them just theyre supposively race pistons and I would to keep the DT reliable.

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i use proxy which is a good piston but a lot cheaper than wisco piston

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i see what you mean i might get another dt and sumo it and keep that for work etc

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My DT had a Wiseco in it for years before I had it rebored , the piston was still good , just worn bore . I think Wiseco pistons are forged rather than cast , cost more to make ,takes longer to warm up but they are stronger.



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Hello mate had same problem your describing after buying a whole engine ran fine then cut out wouldn't start again next day started but backfired bogged the lot your piston looks the same as mine ended up like one I took it apart the piston was ****ed so had it bored replated now it's brand new I'd say piston ****ed new to be redone self experience mate so know what u mean

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Dan Hannam


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IMG_0193.JPGIMG_0195.JPGIMG_0197.JPGIMG_0201.JPGIMG_0203.JPGIMG_0204.JPGthanks mate heres the pictures



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i dont know how the bore can be this straight after this?

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Looks like u got lucky hate to see what could be in your bottom end after that :/

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Dan Hannam


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Looks poggerred to me matey.

Next time remember.

Decent oil and allow for a break in period.

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the barrel is dirty but there are no scores ,really this should have gone bang i have no idea why it didnt

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this is really interesting to read.... ive got an 06 plate dt and since friday ive had the same problem..wont go above 4-5k and ifit does sounds like its gunna fall apart...42mph is my top speed without sounding like im gunna blow up! i was running **** oil at the time and had been thrashing my bike...gunna check it myself ina sec but its booked in for a rebore next friday as i had this problem before and guessed what it was...has anyone worked out how they keep running though and dont go bang?!:s

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Cause it's a mechanical object. It won't just go Bang.

The only way it's going to stop is if something stops it.

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i suppose thats true....well ive got a problem...my piston is fine and the rings are fine.... dont have a camera phone but the rings are poking out 1-2mm and the piston is still perfect silver with no score marks looks brand new! after 6000miles:S spark plug is black and i do have black resin on my tailpipe.... whatdyou reckon?! ive been told check carb replace spark plug and check air filter?

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Check the YPVS

Check fuel/air mixture.

Check restrictions

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how do ii check the ypvs? never altered it in my life as dint know what correct setup wwas.... and how do i check mixturE? just bought a ngkraciing goldtip plug forit.......gunna take carb off n check that as been topld could be main jet blocked....thanks for youre help

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Best plugs you can get is the iridium spark plugs.

YPVS. Well when you turn the ignition on does it do the cleaning cycle.

When open fully does it sit flush with the exhuast port.

Take the cap off. Is the prongs lined up with the whole.

Plug chop will tell you if it's setup correctly.

A way to check is if you take the snorkel out does it run better. I.e. are you now able to achieve higher speeds.

If this is the case then you've got too much fuel and it'll need down jetting.

If te reverse happens you'll need slightly bigger jets.

NORFE reckons that the bike runs fine at standard settings. So it's best to leave it that way. Have standard jets and air intake. Even with an aftermarket exhaust.

That's always first point of call if the bike isn't running right. Return it to factory. Then if you want more power you can adjust.

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ok well i jus fitted the gold tipped one havent turned it over yet will be doing so in 5mins
il check to see ifit does the cycle..im pretty sure it does idve noticed ifit didnt i think.... okkkk and plug chop? :S

my snorkels never been on there but i have old one from previous dt will fit that later and see ifit changes anything(its at my dads) and im running a 230 jet with a full dep with snorkel removed ...airbox is clean just checked it

main jet had a few little rocks enit so hoping it was that simple!:)

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How did you remove the 'rocks'

Compressed air yes?

I'd get yourself a snorkel.

Make sure the float chamber is correct height?


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