Squeeze the fuel primer pump in your hand to check for resistance. If you are unable to pump the fuel bulb, it may mean mean that inadequate fuel is getting to the engine and the fuel line assembly needs to be replaced. Check that you have enough fuel in the tank and that the fuel is not older than 30 days. Fuel that has been sitting for longer than this can become contaminated and will create difficulties with starting the motor. Inspect the fuel lines and connectors for any wear and tear.
Inspect the inside of the plastic engine cowling for any signs of oil residue. If you notice oil, the rings may be bad. Have a qualified marine mechanic check this out for you.
Remove the spark plug and examine it for excessive dirt or corrosion. Clean the plug with a sandblaster or replace if needed. A plug that is good will usually have a gray hue to it.
Check the seal (1/8-inch gasket) between the power-head and fuel pump for any cracks or damage. Have a mechanic replace the gasket for you if necessary. A damaged gasket will cause a vacuum leak in the system.
Squirt a small amount of fuel directly into the carburetor if the outboard motor does not start after priming the fuel bulb. Do this especially after the engine has not be started for a prolonged period of time. Pull the starter rope directly after pouring the fuel into the carburetor.
Inspect the fuel pump cover for any wear and tear. If the cover if cracked, this could also be a source of vacuum leak when the fuel is primed.
Check the fuel pump for leaks. Remove the pump screws and pump (with the engine off) the fuel primer. If you notice gas leaking from a small hole at the rear of the pump, the diaphragm may be damaged.
Test for adequate engine compression. Remove the spark plug and attach the compression test gauge. Check the reading. If it is not between 60 psi (pounds per square inch) and 90 psi, have a qualified mechanic investigate this problem further for you.Evinrude and Johnson, now combined into one company, are well-known names in the boating world and their outboard motors are on numerous boats worldwide. Before gearing up for the season, run through a troubleshooting checklist to make sure your 35 hp Johnson outboard motor is in top working order. Troubleshooting problems that may arise is usually straightforward, whether it's an oil leak or gas leak. Run through these basic steps before calling in a marine mechanic.