1991 DR250 stalling after warmed up

Discussion in 'Thumpers' started by 1994klr250, Sep 13, 2012.

  1. 1994klr250

    1994klr250 Long timer

    Joined:
    Aug 16, 2007
    Oddometer:
    1,091
    Location:
    Southeast michigan
    I've been helping a buddy of mine with a 91 dr250. It needed a bit of maintenance as it had been sitting for about 6 months. I disassembled and cleaned the carb, re-jetted from pilot jet from 40 to 42.5 and main jet from 132.5 to 135, and put new fresh gas in the tank. Idle mixture screw at 2 turns out, new spark plug, and air filter is clean. I can get it to run after a few kicks and it will run for about 5 minutes until it warms up, but it starts to stall after that and its hard to keep running. Once it stalls it won't restart, it tries to go but just dies. If you let it cool off for about 15 minutes it will start right up. I'm thinking the valves might be a bit tight as I haven't had a chance to check them yet. The bike only has 4,000 original miles on it. I'm not sure if the previous owner ever checked them.

    I looked up the valve clearance specs and intake is supposed to be .002-.004 in and exhaust is supposed to be .003-.005 in. For an air cooled engine it seems rather tight to me. I'm used to my klr250 at .008-.009 in on a water cooled engine. I have notice on later dr350 models the exhaust clearance has been increased to .007-.009 in. Does this sound like a possible reason for the hard starting while the engine is hot? Thanks, Fred.
    #1
  2. 1994klr250

    1994klr250 Long timer

    Joined:
    Aug 16, 2007
    Oddometer:
    1,091
    Location:
    Southeast michigan
    Any dr250 or dr350 experts care to chime in?
    #2
  3. jon6.0

    jon6.0 Been here awhile

    Joined:
    Jun 7, 2008
    Oddometer:
    546
    Location:
    Phoenix
    Could the choke be malfunctioning?
    #3
  4. 8gv

    8gv Long timer

    Joined:
    Nov 22, 2009
    Oddometer:
    4,090
    Location:
    CT exile now in NH
    So I'll just make this shit up...

    Questions:
    Since you owned it, did it ever run right?
    Did it run well prior to the re-jetting?
    Can you undo the jetting and see if it runs ok?
    When it quits, do you have spark?

    Yes check the valves.

    My W.A.G.'s:

    You're way too rich. Just as a bike doesn't like choke after it warms up, your extra rich mixture is only tolerated while the bike is cold.

    You have valves that are so tight that compression is lost (not likely because valves that tight usually don't even allow it to start).

    You have an ignition component that has partially failed and is sensative to heat.

    Your 15 minutes is how long it takes for the carb to starve for fuel due to a float or, more likely, a fuel tap issue.

    All of the above comes with my 5 minute, 5 mile warranty.:deal
    #4
  5. jules083

    jules083 Long timer Supporter

    Joined:
    Jan 26, 2011
    Oddometer:
    8,079
    Location:
    Richmond, Ohio
    Give spark a check also. I have an XR250 that had a similar problem, as it was warming up the spark kept getting weaker. Not sure what it was, I picked up a cheap parts bike and swapped everything over, I didn't feel like messing with it.


    It actually sounds exactly like my Farmall (tractor) when the resistor was going out. Same problem there, the warmer it got the worse the spark was. When it would start missing real bad I had about 5 or 10 minutes left where I could un-hook the equipment in the field and limp it home, playing with the throttle, choke, and clutch the whole way.
    #5
  6. Jacl-Kampuchea

    Jacl-Kampuchea Booze Merchant

    Joined:
    Sep 27, 2010
    Oddometer:
    933
    Location:
    I see Drunk People.
    I have one of these.

    Assuming it ran fine before and you just altered the jetting then there's the problem.

    Definitely an air/fuel mix issue, assuming no leaks elsewhere.

    Normally a bike that would outlast a nuclear winter.
    #6