Hello: I have a 2002 Polaris Sportsman 400 that will run about one minute, then for 2 or 3 seconds the spark visibly weakens as observed thru the bulb of my inline spark checker, then the spark dies completely. It will then have no spark at all while cranking. If I let it sit for 15 to 30 mins it will start and run fine for another minute until it does the same thing. I replaced the ignition coil under the front but it has made no difference. Good spark until it runs about a minute, then dies. Can anyone help?