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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10621
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have Mercury 150 xr6 after running then stop to fish bulb

Customer Question

I have Mercury 150 xr6 after running then stop to fish bulb will be empty but not collapsed I have put 2 new bulbs and it still does it. I can pump ball and runs fine at top speed never misses or cuts out. But I stop to fish a while again and bulb has no gas I pump then fine.
Submitted: 2 months ago.
Category: Boat
Expert:  Jason replied 2 months ago.

Hi Rob, my name is Jason.

What you are describing isn't necessarily a problem. How long have you owned this engine for and has it ever been any different in the past for you?

Customer: replied 2 months ago.
4 years. Started last year intermittent wouldn't want to take gas to get on plane. Then it would at ran great at top speed. I had filter changed and diaphragm on pump and new bulb and hose
Expert:  Jason replied 2 months ago.

Okay. What kinds of questions did you have? How is it I can help you?

Customer: replied 2 months ago.
What can cause this issue.
Expert:  Jason replied 2 months ago.

When you say "this issue" do yo mean intermittently not making full power?

Customer: replied 2 months ago.
The bulb will be out of gas after I run then stop to fish it has to be pumped. It's not concave just no gas.
Expert:  Jason replied 2 months ago.

That's normal. When the engine runs the fuel lines and bulb are under a vacuum. The bulb is never actually completely full of fuel when it runs, there is only some fuel in it. When you shut if off the vacuum stops, and some of that fuel can flow back to the tank.

Expert:  Jason replied 2 months ago.

Was there anything else?

Customer: replied 2 months ago.
I never had to pump bulb in past something is causing this.
Expert:  Tan replied 2 months ago.

Hello. My name is Tan.

This is most likely the anti siphon valve in the top of the fuel tank. The anti siphon valve keeps the fuel from siphoning back into the tank and is a safety valve if the fuel line breaks and falls into the bilge it won't siphon all the gas into the bilge causing a fire explosion hazard.

What you will need to do is pull the fuel line off the connection on the fuel tank and remove the fitting. This fitting is the anti siphon valve. It has a spring and a ball that will stick causing the fuel to siphon back into the tank drain back into the tank.

Does this make sense?

Customer: replied 2 months ago.
I've done that this one didn't have valve just nipple
Expert:  Tan replied 2 months ago.

Ok the only other thing that can cause this issue is blockage in the fuel supply in the tank. Have you run the engine on a different fuel source? Does it run the same?

We can do a test to verify a fuel restriction.

Customer: replied 2 months ago.
No I have not. Could anything like carb or fuel pump cause this.
Expert:  Tan replied 2 months ago.

The fuel pump could cause this issue as it has check valves in it. You said the pump has been done? Did they do just a diaphram?

Usually you will have engine performance issues with a bad fuel pump. The carb will not cause this issue.

Customer: replied 2 months ago.
Just diaphragm installed
Expert:  Tan replied 2 months ago.

Ok I would try the other fuel source to eliminate an issue with the boat side fuel system. If the engine runs the same then we need to do a complete rebuild on the fuel pump.

Post your engine serial number and I can get you the part number and a link to the rebuild kit for the fuel pump.

Customer: replied 2 months ago.
If it is pump would it run fine at top speed never an issue at top speed
Expert:  Tan replied 2 months ago.

Yes top speed will be fine. The valves can be bad and it will still pump fuel. If the valves are worn it will cause low speed problems and fuel siphoning back into the tank. So what is happening is the engine is loosing prime due to valve failure or a restriction in the tank causing a vacuum sucking the fuel out of the line when you shut engine off.

The most likely cause is the fuel pump.

Customer: replied 2 months ago.
Ok thanks.
Expert:  Tan replied 2 months ago.

Your welcome.....Please don't forget to positively rate my help as that is the only way I get paid.

To rate click on the stars at the top of the page 3 or more please.

Follow up questions are always welcome.

Thank you.....Tan

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