Logo

Yamaha 40 auto lube

johann

New member
Hi guys

I need help with my boats outboard. It is a Yamaha 40 .3 cillinder.The motor was fine and one day started to lose power when it is open throttle. It sounds as if it is choking and the nice purr sound on the motor is gone. It is a pull start and started perfectly. Once it is open throttle it would run nice for a few seconds and then loses power. I replaced the spark plugs. The sparkplug wires,the fuel filter is clean, new fuel pump carbs been opened and cleaned, new fuel line/hand pump and fuel tank. Another Yamaha 40 electronic black box was borrowed, no diff. I then checked the reed valves ,all fine. Just replaced the head gasket, as I thought it was maybe busy blowing and the water kills the spark on the plugs. No success. PLEASE HELP!!! Has anyone ever had a similar problem? It may sound as if I tried to fix it myself, but the motor was at our local boat mec. and even he doesn't know. And yes we have checked the wiring several times. Can an outboard exhaust get blocked? Please if you guys can give me some advice I would appriciate it a lot. I brought the boat for fishing, this season the fish had a laugh at me with my 2 stroke 40 Yamaha.
 
Is the engine getting to operating temp. You need to run it and check it with an IR temp gun. Did you replace the water jacket gasket on the Cylinder head?

When was the last time the carbs were cleaned?
 
Yes I replaced the water jacket gasket on the Cylinder head. The cooling system operates fine. New impellar. The carbs has been serviced and looks like new. My suspision is that is the carbs, although it has been serviced.
 
When you remove the carbs, remove the float bowl, the float and the needle valve. Blow air from the needle seat back out to the fuel connection and catch the dirt that comes out. This is often missed.
 
Back
Top