I have a ltz 400 and it starts up and runs great for about 5-10 min. Then it pops and sputters and backfires. I have taking off carb and cleaned and tuned it to many times to remember I'm thinking its not a fuel prob. And its spark related, have replaced coil so I'm thinking its the cdi. Box. But there pretty pricy so want to make sure that's the prob. I would appreciate any input thanks

 

Have you checked for a blockage in the fuel tank vent?

Don't know the LTZ but someone on here is having similar trouble with a Kawasaki. It is overcharging. First thing is to check the voltage at the battery, shouldn't go over 14.5v with the engine being revved. In theory this shouldn't affect bikes with AC ignition, but I had an Arctic Cat (Suzuki engine) that regularly cooked plugs, and it turned out to be an overcharging voltage regulator.