• Global Moderator

    I managed to contact the original owner of my TDR and he gave me a little bit of info about the history of the bike. Among other things, he told me that it has been up jetted from stock. I did suspect this as the air box has been slightly molested...


    The bike does seem to run nicely, but I'm just wondering what differences I would see if I put the stock jet back on it and repaired the air box?

  • Whats the current settings of the carb?

    I can't see it being much different from a dtr to be fair. Unless it's the Belgarda or the 4FL Spec.

    Which as I recall yout tdr is the European 4FL? In which case it's quite possible.

    If it's not running right then just set if up so it is.

  • Global Moderator

    4FU from Germany. As I say, it is running fine but never really changed jets before so not too sure if it there would have actually been any noticeable gains from the upjetting or if it was a waste of a perfectly good airbox.

  • @MIGHTYMAN So I was in Skellerns Yamaha recently and they have got a Yamaha TZR 125 RR SP in there. And he was just having such a faff trying to get it jetted perfectly. After some time he decided that it simply was not getting enough air, he lopped off the whole of the top of the air box, jetted it accordingly and he said what a difference it made.

    He said rolling start in second gear doing 9mph, he rolled the throttle wide open on a mapped out piece of road 1/4 mile long. He said by the end of the 1/4 mile he looked down at the clocks and it was past an indicated 100.

    He is a life long mechanic and a proper two stroke nut. And he is convinced the air boxes are what are holding the engine back.

    Now my question is why do you want to up jet it. If it's for more power then you will only get more power with supporting mods. Upjetting is a mod, you need the others to actually make more power, else it'll run worse. The aim of the game is to match the fuel with air exactly, thus running the engine very close to lean. Upjetting won't therefore give you more power. Unless you marry up the extra fuel with air molecules.

    If however it's not running right, then you want to know why that is the case. It may be running.too rich, in which case smaller jetting.is required.

    Easy way to test is to restrict the air box, if it's running better than you know there is not enough fuel. If worse then it's running rich.

  • @MIGHTYMAN said in Is upsetting necessary?:

    4FU from Germany.

    Not talking about the cylinder pal. Was talking about the Chassis/Engine code. Not that it makes too much difference but the 4DL's are ever so slightly different internally compared to the 3BN.

    Finding out it's a 4GW model will tell you what spec the engine was, I.E 4DL ran VHSA carbs over the 3BNs Mikuni TMX28. Stuff like that just tells you a bit more about the problem.