Odd Happening

Discussion in '2 smokers' started by MC_Collector, Oct 11, 2020.

  1. MC_Collector

    MC_Collector Retired and riding!

    Jan 15, 2008
    Mountain View, Arkansas
    Something really odd happened to me recently. I have a 1977 Yamaha DT250D 2 Smoke. It has a Mikuni VM28 carb with the standard carb mounted lever enrichiner setup. The carb doesn't have a accessible drain and I have been in the habit of turing off the gas and running all the gas out of it when parked for a while. This and non ethanol gas has kept me out if carb problems for some time. The last time I did this, I turned on the enrichiner as I generally do, but opened the throttle as I thought it was sucking up the last bit of fuel. At this point, the engine revved to 7000 and after releasing the throttle it hung there. I turned off the key and it stayed there for several seconds. Finally, turing off the enrichiner killed it. After cooling off I started it back up and it seemed completely normal. The engine was hot when I ran the gas out and I'm guessing it was running with heat generated from the lean mixture and ambient heat like the model airplane engines I played with as a kid. I'm positive there is no sticking throttle and the switch grounds the magneto ignition. Anybody have other ideas?
  2. franko58

    franko58 Been here awhile Supporter

    Jun 21, 2015
    Fort Atkinson, Wisconsin
    Could the slide have hung up due to oil residue from a oiled filter building up on it?
    As for the ignition, that could be from a hot piece of carbon in the cylinder.
  3. concours

    concours WFO for 50 years

    Dec 2, 2008
    NH USA
    Like you guessed (model engine glow) it was dieseling. Bits of hot carbon on the plug can do it. my 1969 JT-1 would do it
  4. Euromad

    Euromad Been here awhile

    Feb 16, 2010
    Lower Slobbovia
    Yep. You were running very lean it got hot enough to diesel.