TIMING CHANGE - Mere 1500-1400-1350-1150

Old stuff, but there are still a lot of these motors in the field.
This includes both units with belt driven distributors and those with the timer base under the flywheel.
There have been instances of piston detonation and/or scoring on current model 6-cylinder Mercury  Outboards. Part of this problem has been attributed to:
a. Lower than recommended octane gasoline and/or
b. Incorrect propeller installation (too high a pitch propeller for the particular application).
  When servicing Mere 1500-1400-1350-1150 Outboards for any reason, retard the spark to 21  BTDC. If detonation and/or piston scoring are experienced, retard timing on those specified models  in your area so that they are more tolerant to the occasional lower-than-recommended octane  gasoline that reaches the marine market. No significant loss of performance will he observed from  the 2% spark retard. Merc 1500 and 1150 models above Serial No. 4·23984 will have a spark setting  of 21 BTDC from production.