I have a '04 LT-Z400 with a slip on Yosh and Pro-design intake. My problem is when this thing is nice and cool it runs great for about two minutes until it is warmed up. Then it starts poping and backfiring around half throttle real bad. Still runs good at idle and full throttle until around another two minutes and then it starts cutting out at full throttle too. It continues to cut out worse and worse until it will die sometime around the five minute mark. Then it will not start again until it cools down. I've had the carb opened about 20 times, checked the diaphram, checked all the passages, checked everthing in the carb. I've pulled the gas cap off thinking it might be vapor locking, still not it. Checked compression, 115 lbs. so that's good as well. Changed the spark plug and that made no difference as well. So tonight I checked resistance in the trigger coil (531 ohms), and the source coil (.3 ohms) and they both checked good. Then I checked peak voltage on the trigger coil, it came to .13 VDC and is supposed to be 2.0+ volts. Also the peak voltage on the source coil, it came to .04 VDC and is supposed to be .10+ volts. I'm wondering if anyone else has seen this problem. I'm about to pull what is left of my hair clear out on this thing...

CJ

 

So, I just found the problem! The stator's rotor was rubbing on the pickup coil wires and was apparently shorting out the signal to the CDI! I've only spent about ten hours trying to figure out what was wrong with this thing... apparently I just needed to type it out.

 

good work