Fuel pump problem today

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jfo137
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Fuel pump problem today

Post by jfo137 » Sat Dec 03, 2016 4:10 pm

Ok, I go out to do my weekly run of the MB. 1. Give the fuel pump primer handle a few pumps. I can feel it moving the diaphragm and I can hear the fuel moving. 2. Crank it over and no start. 3. Lets retry the primer... now it feels like it's not moving the diaphragm or moving fuel. 4. Unhook fuel line and can blow air bubbles back into gas tank. 5. Pour gas into carb and she fires right up but will only run on gas in the carb.

So before I get crazy and start tearing apart the fuel pump any thoughts on what the fuel pump issue might be? It is the original fuel pump that was rebuilt two years ago and has been fine since. Thanks for your thoughts and help.


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Scoutpilot
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Re: Fuel pump problem today

Post by Scoutpilot » Sun Dec 04, 2016 2:01 am

Are you certain there was no fuel in the carburetor bowl? When I prime the carb with the manual lever, I listen to the fuel rushing into the bowl. After about 10-12 strokes, the sound stops. The bowl is full.
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Re: Fuel pump problem today

Post by artificer » Sun Dec 04, 2016 7:48 am

jfo137 wrote:Ok, I go out to do my weekly run of the MB.
1. Give the fuel pump primer handle a few pumps. I can feel it moving the diaphragm and I can hear the fuel moving.
That is normal
2. Crank it over and no start.
3. Lets retry the primer... now it feels like it's not moving the diaphragm or moving fuel.
That is normal when the fuel bowl is full & the float closes the needle valve or the fuel pump lever is on the top of the cam.
4. Unhook fuel line and can blow air bubbles back into gas tank.
5. Pour gas into carb and she fires right up but will only run on gas in the carb.
This is just the gas poured in the carb? So how long does it run?
So before I get crazy and start tearing apart the fuel pump any thoughts on what the fuel pump issue might be? That would not be very smart, seeing the fuel pump has not been tested & by the description it sounds like the fuel pump is working fine.
It is the original fuel pump that was rebuilt two years ago and has been fine since.
What fuel related work has been done recently? Is the choke being used because it really sounds that after the fuel pump testing & elimination one should be looking @ eliminating an idle circuit issue.
Remove the fuel line @ the carburettor & with the ignition off crank the engine & ensure the fuel pump has an acceptable stream of fuel from the fuel line.
Test with a fuel pump vacuum/pressure tester you can get for <$16 then use for this & other testing.
http://www.harborfreight.com/fuel-pump- ... 62637.html
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Re: Fuel pump problem today

Post by tamnalan » Sun Dec 04, 2016 1:37 pm

If the engine cam lobe happens to be pushing and bottoming the pump lever, then the primer handle has no effect. You might try to bump the motor a bit and then try the primer lever.
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