Odd Happening

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

  1. MC_Collector

    MC_Collector Retired and riding!

    Joined:
    Jan 15, 2008
    Oddometer:
    141
    Location:
    Longshot, Mississippi
    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?
    #1
  2. franko58

    franko58 Been here awhile Supporter

    Joined:
    Jun 21, 2015
    Oddometer:
    253
    Location:
    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.
    #2
  3. concours

    concours WFO for 48 years

    Joined:
    Dec 2, 2008
    Oddometer:
    7,824
    Location:
    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
    #3
  4. Euromad

    Euromad Been here awhile

    Joined:
    Feb 16, 2010
    Oddometer:
    537
    Location:
    Lower Slobbovia
    Yep. You were running very lean it got hot enough to diesel.
    #4