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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10630
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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If motors 't push boat in occasion what can it be

Customer Question

If motors don't push boat in occasion what can it be
Submitted: 11 months ago.
Category: Boat
Customer: replied 11 months ago.
It sound like the motors have the power but soon after given full throttle they both die
Expert:  Tan replied 11 months ago.

Hello. My name is Tan.

Since both engine are doing the same thing it has to be fuel related. To determine if this is a fuel related issue you will have to run both engines on a different fuel source or have a friend squeeze both primer bulbs when the engine are acting up.

Can you do this test and post back with results?

Does the boat have one fuel tank for both engines or separate tanks for each engine?

Customer: replied 11 months ago.
Both engines same tank I did squeeze pump and stay flat
Customer: replied 11 months ago.
When I squeeze motor seem to work a bit better but them pump stay flat and motor die
Expert:  Tan replied 11 months ago.

Ok you have a fuel restriction in the fuel tank as that is why the primer bulb is collapsing. You have debris in the fuel tank clogging up the pick up tube. This means you will have to pull the pick up tubes out of the tank. Remove the screens on the ends of the pick up tubes and pump the debris out of the fuel tank. The pick up tubes are where the fuel line connects to the fuel tank.

To pump the fuel tank you will have to remove the fuel sending unit and pump the tank from that opening.

When you get blockage in the fuel tank it creates a vacuum to the point it will suck the primer bulb flat and the engine will quit as it has no fuel.

The other possibility is a clogged fuel vent. This can be tested by removing the fuel fill capo and running the boat. If the engine run better then the fuel tank vent line is kinked or clogged.

Now since both engines are doing the same thing the fuel tank is the problem.

Post back with questions.

Thank you.....Tan

Customer: replied 11 months ago.
Hi tan
I removed pick up lines and they seen to be clean I recently also change the filter on the gas vent I use to have a lg50 but I replaced it with a lg100 a bit bigger including vent valve
Expert:  Tan replied 11 months ago.

Did you remove the pick up tube from the tank and do they have screens on the ends of the tubes?

Customer: replied 11 months ago.
Screens in the tuve small one inside
Expert:  Tan replied 11 months ago.

Remove the screen. What happens is the debris floats around in the tank then when you run the engine at higher rpms the fuel volume is greater which causes all the debris in the tank to get sucked up to the screen till it starves the engine for fuel. This is why the engine will run at lower rpms as the fuel volume isn't as great and the debris isn't pulled to the tube.

Customer: replied 11 months ago.
What else can it be if not that thanks for your advise I just got the boat and sucks no to be able to run it
Expert:  Tan replied 11 months ago.

The only thing that will cause the primer bulbs to suck flat is a restriction in the pick up tube, bad primer bulbs or bad fuel lines coming from the fuel tank.

Customer: replied 11 months ago.
I replace line from tank out to motor unless is primer bulbs
Expert:  Tan replied 11 months ago.

Since both engines are doing the same thing it isn't likely you have 2 bad primer bulbs. So the common to both engines is the fuel tank. If you have debris in the tank it will affect both engines. To verify this run the engines on a different fuel supply. Get an auxiliary fuel tank and run each engine on the tank. Do the engines run better?

Customer: replied 11 months ago.
I haven't done that if they fun better what's next step ?
Expert:  Tan replied 11 months ago.

Remove the fuel sending unit from the top of fuel tank pump all the fuel out of the tank and inspect for debris. Remove the screens from the ends of the pick up tubes.

Customer: replied 11 months ago.
Where is this guilt sending pump located ?
Expert:  Tan replied 11 months ago.

I have no idea what a guilt sending pump is?

If you are referring to the fuel sending unit it is located in the top of the fuel tank. Where exactly I have no idea as I don't know the make model of your boat. All fuel tanks have a fuel sending unit which sends the signal to the fuel gauge to tell you the fuel level in the fuel tank.

Expert:  Tan replied 11 months ago.

Here is an example of a fuel sending unit in the top of a fuel tank. The round disc with the green and pink wires is the sender.

http://s189.photobucket.com/user/kalel76/media/PICT0009x.jpg.html

Customer: replied 11 months ago.
Is clean it just a rod with a float at bottom end of rod
Customer: replied 11 months ago.
Don't see any house for suction may be that's Damaged
Expert:  Tan replied 11 months ago.

The sender has nothing to do with your problem it is where you have to access the fuel tank to pump the fuel out to clean the tank.

What part do you not understand about debris in the tank causing a fuel restriction? Maybe I am not being clear enough.

Expert:  Tan replied 11 months ago.

To pump the tank you have to get your own fuel hose and a pump to pump the fuel out of the tank.

Customer: replied 11 months ago.
Understand thanks
Expert:  Tan replied 11 months ago.

Ok post back if you have further questions about this issue.

Please don't forget to positively rate me for helping you as that is the only way I get paid.

Follow up questions are always welcome at no extra charge on this subject.

Your welcome............Thank you..........Tan

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