I have a 99 TRX300 that starts and runs good for about 30 seconds. After that it will idle fine but will pop out the exhaust and sputter if you give it throttle. If you press the start button, with it running, it runs perfect for 3-5 seconds then back to backfiring. I have replaced the CDI box and Coil, the coil was a little high on the primary and secondary when ohm checked. All other resistance checks were in spec to the manual and the coil input was just under 200V when DVA checked. Any thoughts?