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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 2014 Yamaha 40 four stroke when I'm running wot or

Customer Question

I have a 2014 Yamaha 40 four stroke when I'm running wot or planning it runs fine . when I idle for a long period of time the motor will run out of fuel I have to pump the primer and it'll start back up and run wot all day just when idling it runs out of fuel .what could possibly be wrong ?has new hose and new tank and new primer
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello Raymond. My name is***** is fuel delivery issue due to a possible sticking anti siphon valve or fuel pump failure. Run the engine on a different fuel tank. Will it idle now? If it idles now then you have an issue with the original fuel system. If no change then the fuel pump is to weak to pull fuel to the engine. When you squeeze the primer bulb you atre doing what the pump should be doing. Post back with questions and findings.
Customer: replied 1 year ago.
I just changed the tank n hose n primer bulb and added a water fuel seperater when the problem first started I don't understand how the fuel pump will be weak to send fuel on idle but wot it will keep it all primed up
Expert:  Tan replied 1 year ago.
The pump is a mechanical pump and won';t pump as well at lower rpms if it has a bad diaphram. It will pump at higher rpms as the rpms are higher. The faster the pump pumps the better the fuel pressure. Now I didn't say the pump was the problem I said after you have eliminated the boat side fuel system that leaves the puimp as the problem. Did you have the problem before you did the changes?
Customer: replied 1 year ago.
Yes it started before I changed all the tank n fuel lines and primer bulb and all that
Expert:  Tan replied 1 year ago.
Then the fuel pump is weak at lower rpms and can't supply fuel to the engine.If the fuel pump diaphram has a small hole in it the pump can work at higher rpms and not at lower? We know it isn't the boat side fuel system as all of that is new. leaving the only thing it can be is the fuel pump. If it can deliver the fuel then the engine will not run. Just by process of elimination the fuel pump is the problem. Unless you think there is something else that delivers fuel to the engine?Does this make sense?
Expert:  Tan replied 1 year ago.
Will the engine continue to run if you squeeze the primer bulb when it starts to die?
Customer: replied 1 year ago.
Yea I can pump the primer before it dies and take off n it will run fine only idling in gear it does this
Expert:  Tan replied 1 year ago.
The fuel pump is bad. This is called a lift pump and it supplies fuel to the VST(vapor separator tank). So when it doesn't pump enough fuel the engine runs out of fuel. The lift pump is bad. Here is a link to the pump. You will have to remove the pump and disassemble inspect. Then replace any worn parts. # ***** ,23and 28 are the parts that fail.
Expert:  Tan replied 1 year ago.
I usually just replace the complete pump assembly # *****
Customer: replied 1 year ago.
I'll give it a try
Expert:  Tan replied 1 year ago.
Ok that's the only thing it can be you have replaced all the other things that could cause the issue.What is it that you don't under stand about this pump being the issue?