my 1997 670 summit keeps blowing a plug . usually when i first start off, and im using more fuel than normal. any ideas.

I have a '98 MXZ 670. A few suggestions and checks: is the machine sitting level when not riding because if the back end is raised to high the fuel will syphone itself through the fuel pump into the engine and it will flood cause you to use and foul plugs and hard to start. 2nd check the carbs setting right, main jets proper size and needle jets proper position. that last thing would be your needle and seat on your float might need replacing if leaking. Another possibility is your rotory valve timing. Need to check and make sure your rotory valve is tight and timed right otherwise this will cause problems too. I had mine checked by a mechanic as l did not know what l wa doing that. It is only the 583 1nd 670s that have rotory valve instead of reed valves. i am not sure if the 500s had the rotory or not.