DT125R Breaking and Fixing

  • So, here we go

    I brought a DTR last September and it was a brilliant bike for about a month then all of the problems started comming, they were all pretty much fueling related and i had no clue what was going on, each part in the carb was dying 1 by 1. then the powervalve pulley and cables broke. anyway, the fix

    first i brought a new power valve pulley and cables because the old pulley had snapped and the cable frayed.


    also ended up picking myself up a new carb, apparently from a running bike so that i can use the bike and repair the original carb at the same time.


    however this is what turned up, a carb from the older dt's i think, anyway i ordered another one that was the right one, little bit of repaired damaged, stunk of fuel tho so thats always a good sign.


    i also got a reed block spacer and some new hytech fibre reeds, not sure if my problems were caused by the old ones but new ones cant hurt, right?. the inlet manifold was also changed because some idiot in the past had cut the funnel bit out that directs the air and fuel mix, which may have also been causing my problems.


    so next up was to fit it all, my mum wasn't happy about this but because of the weather down here it had to be done, welcome to my kitchen turned garage


    so the next bit was simple, all i had to do was re assemble it all. which at this point was easy as it had been in bits so many times before. Starting with the Reeds, Manifold and Spacer. also a few home made gaskets were added, these were a pain to make to because they had to be so thin.


    next was the carb and the boost bottle, these fitted straight in like this. the hard bit though was trying to refit the air box, even with out the spacer this is still a job getting in, anyway eventually it went in and the bike was put back together.


    So did it work, sort of, the main jet was a 240 in the new carb and it looked pretty good inside, it ran for like 5 mins the just wouldn't start again, did a plug check and it was covered it fuel, so ill try making it leaner today, so i guess the mixture screw is done up to do that???

    Also on a side note has anyone ever made their own dogbones for the suspension, i did a first attempt at work yesterday out of 5mm lcs and its defiantly not strong or thick enough to do the job, just wondering what other people used. the plans were of someone on this website (obviously i didn't finish them because i knew they wouldn't work. not the plans the metal used)


    Any more suggestions on what to do would be great. 🙂

  • Hi there.

    Shame about the luck but don't dispair. Two strokes are incredibly simple so it shouldn't be too much causing the issues.

    Ultimately I would say this.

    For combustion to happen you need three things.


    It's obvious to me you have fuel, air is most likely guaranteed too

    I would start by investigating the spark situation.

    If it's a weak spark then you will need to check some other ideas but start simple like plugs and coils.

    When the throttle is closed the richness of the fuel.is determined by the air screw. I believe the factory setting is two and half turns from closed. If it's running fine, once warm, when that's done, but horribly in other areas of the rev range then this is determines by the needle. The main jet is only a factor in wode open throttle scenarios.

    Of course for the bike to maintain combustion the engine must be healthy. An engine past its best will be hard to start and will seriously lack performance.

  • thankyou
    spark was great and arc'd to the frame even, it was another case of a dodgy plug, even though it seemed to work it didnt, i replaced it with an old iridium br9iex and it started fine first kick, bit rich but thats sorted now, and it kept a steady idle for about 10 mins without choke.

    it threw out loads of rubish from the end can though, i guess this was what was left after all the failed attempted kicks.

    anyway ill keep you all updated

  • G Reg? I'm sure the carb you bought was correct for the year.

    Although you don't want a round slide carb anyway lol.

    If it's got a good spark then that's good news. Iridium should help it start better.

    My bike has never started without choke, unless warm.

    Sometimes when there is no battery installed, or it's weak, it can cause abnormalities in starting and running.

    So what you mean now then, is it all working as it should?

  • @Calum
    its all working as it should now, the bike is also 2001 the plate is a private one haha, still need to adjust the mixture a bit but ill wait for it to be dry for that

  • @AlfieHopkins yeah fair enough. Was going thinking that's odd for a G plate?

    I will get a private plate for my bike once it's finished. Am usually not bothered but because it's one of a kind I think I will just as a finishing touch!

  • @Calum i have custom dog bones on mine. Slightly shorter which raises the height. You want me to sketch it out and take measurements.

  • @Calum i have them sketched out already i think the centers of the holes are 85mm apart for a 25mm rise?, i need to find some thicker metal somewhere aswell maybe stainless steel to, that would be stronger