20 Most Recent Yamaha 40N/50N 40 and 50 HP Outboard Motor Service/Shop/Repair Questions & Answers

Where do you connect the 12 v battery power cable to the engine on a 4stroke 40 hp yamaha year 2005.

Year and model?

Your fuel pump is connected to the block which experiences positive and negative pressure. As the piston moves up it sucks fuel and air into the block. As the piston moves down it builds up pressure in the block. This pressure is used to force the fuel air mixture into the inlet port of the cylinder. So what you think is exhaust pressure is a normal condition. Get a rebuild kit and rebuild your fuel pump.

2 or 4 stroke?

Are the controls for the 'fast idle' loose? Also--run some seafoam through the fuel system on a regular basis--one per month.

This can have some reasons: 1 clogged carburettors. Too less fuel means a hard start. 2 Worn spark plugs 3 Loss of compression... On a 2-stroke, measuring compression is not an exact science. Have throttle wide open. No spark plugs, check compression on all cylinders. They should be all within 1bar from eachother...

It's located on the port side of the engine, You'll see just before the spark plugs the exhaust cover. At the top a cap, held with 2 10mm head bolts. There is the thermostat. But, most of time the impeller parts will stay stuck in the tube between pump and engine block...

Need to hook up YDS diagnostics and check for codes first. Second you need to hook up a fuel pressure gauge on the motor and make sure your keeping steady fuel pressure. Did you check the grommet on top of the high pressure pump for a split in the rubber?

One cylinder may be starved for oil causing the noise your hearing.

Some grease on the end of the trim rams and see if it don't go away.

Not enough information, but there are two things I didn't read about you checking. Make sure the fuel quick connection on the engine (and possibly the fuel tank) is locked all the way in first, Then see if your fuel pump is working. Disconnect the fuel line from the carb and, holding it in a gas can, have someone turn on the ignition. If It's an electric pump, it should start running fuel, if mechanical, they'll have to crank it a little to get fuel going. If you get plenty of fuel that way, your float in the carb could have gotten stuck, or something in the line got into it.

Here you go: http://www.yamaha-motor.com/assets/service/manuals/1/lit-18626-06-58_1385.pdf