How to Troubleshoot a Yamaha 4-Stroke Outboard Motor

by Brianna Collins

three huge motors on a boat image by Dev from Fotolia.com

Yamaha offers consumers great variety with its four-stroke outboard motor lineup. In 2011 alone, the company featured 10 different four-stroke makes with dozens of different models. Each had unique engineering specs, power capabilities and intended uses. But despite this great variety between different models, Yamaha's troubleshooting tips remain nearly identical for all of the company's four-stroke outboards. Yamaha includes troubleshooting tips and specific part requirements in the owner's manual for each of its outboard motors.

Starter

Step 1

Use the Yamaha outboard's starter. If the starter motor doesn't engage and the engine doesn't turn over, the electrical system may be at fault.

Step 2

Check to see if the main fuse has blown on electric-starting models. To access the fuse, unscrew and remove the electrical cover on the top of the outboard and remove the fuse holder with a pair of pliers. If the connection at the center of the fuse is broken, the fuse has blown. Replace it with one of the same amperage, as listed in the "Specifications" section of the Yamaha outboard owner's manual.

Step 3

Check the battery next. The battery should be located somewhere within the watercraft, separate from the Yamaha outboard in a secure and dry location.

Step 4

Disconnect the negative (black) cable first and the positive (red) cable second. Remove the battery from its housing.

Step 5

Scrape away any corrosion from the battery terminals using a wire-bristle brush. Clean away debris or other buildup using a solution of one cup of water and one tablespoon of baking soda. Dry the terminals thoroughly with a clean rag before continuing. If the battery is damaged, replace it.

Step 6

Charge the battery fully using a separately powered charger.

Step 7

Reinstall the battery and battery cables, connecting the positive cable before the negative one.

Step 8

Try the outboard's starter again. If the starter motor still will not engage, have the electrical system inspected by a Yamaha-certified mechanic.

Engine

Step 1

Check the fuel system first if the engine has problems starting or running. Ensure that there are adequate fuel levels in the gas tank. If not, refuel with unleaded gasoline with an octane rating of 86 or higher.

Step 2

Check the fuel lines connecting the outboard motor to the fuel tank. If any breaks or leakages are found, immediately stop use of the outboard motor and take it to the shop for repairs. If gummy or watery fuel is found, have the fuel tank drained by a Yamaha dealer to remove any contaminated gasoline.

Step 3

Check the engine oil levels next. Ensure that the outboard motor is in an upright and level position. Then remove the oil filler cap and the connected dipstick from the oil tank. Wipe the dipstick with a cloth, reinsert it fully, then remove it and check the oil mark on the side of the dipstick. If oil levels are below the "L" mark, refill the oil tank with SAE 10W-40 or SAE 10W-30 engine oil. If engine oil levels are above the "H" mark, remove excess oil using a clean syringe.

Step 4

Remove and inspect the spark plugs. These are located inside the engine case in each of the outboard motor's cylinders. The exact type and number of spark plugs varies according to outboard motor model; this information can be found in the "Maintenance" section of the Yamaha outboard owner's manual.

Step 5

Remove the spark plug cap and twist each plug away from the cylinder using a spark plug wrench.

Step 6

Replace any spark plugs that have a burned, brittle or cracked insulator tip with the type specified in the owner's manual.

Step 7

Measure the spark plug gap with a wire thickness gauge. This gap should fall within the range stipulated in the owner's manual (usually around 0.028 inches). If it is too wide, shorten it by pressing the hook-end of the plug against a firm surface. Widen the gap by pulling the hook wider with a spark plug gap tool.