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What fuel for an old Yamaha DT125?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by listek, Jul 15, 2009.

  1. My wife has somehow recruited me to get her old learner bike going. I think it's a DT125 but not 100% sure - in my defense it's parked behind a pike of stuff in her mothers garage so haven't had a good look at it yet, but it looks like one from what I can see. That makes it a 2 stroke I think, and in its day it would have run on a leaded 2 stroke premix. Of course these days leaded fuel is long gone so is it ok to just use premixed unleaded? The bike has quite a bit of family history as it used to be her fathers (passed away unfortunately) trials bike so the instructions also run to restoring it back to its original glory, plus everyone in her family appears to have learned to ride on this bike.

    I'd hate to kill it unintentionally althought the poor thing's probably hopelessly siezed by now anyway. Be a shame if it was as it looks to be in ok condition cosmetically. Any help much appreciated.

  2. I had a DT50 when I was tiny (showing my age lol), but I seem to remember it having a separate tank for two-stroke oil and it would mix it will the fuel in the tank itself. i.e. not premix! I'm not sure but I would think the DT125 would be similar. Check under the side (plastic) panels on the left or right side (they clip off) and look for the two-stroke oil tank. Also it obviously ran on leaded fuel so I'm not sure how it would run on unleaded (or even if it can!).
  3. The key concerns about using unleaded in 'leaded' engines is pinging and valve seat recession, neither of which are relevant on this bike.

    It will have an autolube injection system, so if all's well there's no need to pre-mix. However, make sure this system is working, if in doubt, pre-mix.
  4. Yep, wot 'e said!
  5. Yep, wot 'e said!

    Lawn mowers that used to run on regular leaded still run just as well on unleaded.
  6. DT125's definitely had an oil injection system. You should have no particular worries with unleaded. It's the valves that usually suffer and since two strokes don't have valves (alright I know there's some "reed valves" and "rotary valve" thingies on some bikes but they aren't real proper valves) :p

    Some stuff about 2 stroke oil pumps here.

    They are however much easier to replace than repair... If you need one, there's quite a few around. Expect to pay about $50 - $60.