I also have a Lance Duke 250. My would start fine but after running a while it would misfire and stall at idle. After much disassembly and testing I found that the spark plug connector was arcing internally and shorting to the metal shield on the connector. For a temporary solution I removed the connector and stripped about an inch of insulation from the spark plug wire and wrapped it around the spark plug stud. It starts and idle like a rock...no more misfire. I could envision your problem to be a more severe case and shorting all the time. Try it..its easy. If still no go then you have to test the ignition. Have you found Stan Jessups website? He has a post of a Honda Helix shop manual which is nearly identical to the Lance Duke 250. The ignition section should prove very helpful. Check it out.