I believe the decompression plugs were originally installed in the 2005 Mach Z's to assist in the starting process. There was some concern that a 1000cc twin would be too hard to pull-start without them - especially under very cold conditions. Following several months of sparkplug fouling problems last year, BRP indicated that the decompression plugs were contributing to the fouling issue. By September, BRP formally recommended that solid plugs be retrofitted to all Mach Z's.
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