Over time the mixture needle O-Ring can soak up excess fuel causing it to compress more than usual which can reduce tension on the mixture needle spring. In some cases this may allow the mixture needle to rotate during operation due to normal engine vibrations. A cheap, easy solution to prevent the issue is to install a second O-Ring on the mixture needle to ensure spring tension is always maintained.
On the rare occasion that this may happen, the O-Ring cost is $1.50ea rrp
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