I purchased a one-owner 600 Grizzly with less than 300 miles on it. For the first two years it started easily and once warmed up it ran very well.

Last hunting season started fine. It suddenly became very difficult to start, cranking until the battery was drained.

Long periods of cranking will cause a coughing (puff) sound and occasional backfire.

I replaced the coil (mounted on the front left side above the tire) but it does not seem to help.

The unit has less than 500 miles on it and I have kept it inside.

Any suggestions for troubleshooting are appreciate.