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See: the above technical bulletin. It address the problem of premature ignition or knock and it says that it will not cure the problem. I think that the 80s to 83 models came under the regulations of the EPA police, and Yamaha leaned the engines down considerably with the jets and timing advance in order to comply with EPA. I think the problem will go away with the enrichment of the fuel and the slight retard of the vacuum advance. My 80G has no knock whatsoever running on 87 fuel, but it may have been modified with the newer vacuum advance unit. I cannot tell.
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