2000-2005 Yamaha F40B Outboard Service Manual, Page 120Get this manual
GENERAL
NOTE: _ Batteries vary among manufacturersTherefore, the following procedures may not always applyConsult your battery manufacturer's instructionsFirst, disconnect the negative lead, then the positive lead-
Check:Electrolyte level Below the minimum level mark Add distilled water to the proper level- Electrolyte specific gravity Less than specification -7 Recharge the batteryElectrolyte specific gravity 1.28 at 20C (68F)
CHECKING THE SPARK PLUGS