Small outboard crank case flooding with fuel

[Valmika]

I have a 2009 Mercury 6hp 4 Stroke. I have gasoline entering my crank case and I don't know why.



I have serviced the carburetor and needle valve and both look good.



I have checked the needle valve with vacuum tester and holds vacuum.



The compression was good.



It's blowing grey smoke even after an oil change. I've done 4 oil changes now to remove all the gas from the crank.



Why is the crank filling with fuel? I am stumped. Any and all advice on how to remedy this problem would be greatly appreciated. Thank you!

[jamhass]

Don't know this OB, but most have a diaphragm fuel pump operated by crankcase pressure/vacuum, so could be a failed diaphragm.

[Empty Pockets]

My guess is it has a diaphragm fuel pump mounted on the crankcase, and that diaphragm is busted and it pumps fuel into the crankcase as well as the carb...
Jam beat me to it.

[Valmika]

We did check the pump and it looked as if diaphragm was intact. We will try to figure a way to pressure test it. I am wondering if the needle valve is faulty even though we tested with a vacuum pump (maybe we were helping it seal) Question: if the needle valve is bad and overflows the bowl wouldnt the just drain out, not get sucked into the carb?

[Var Korall]

On most 4 stroke outboards, if you lay them down with the wrong side up, the gas will drain through the carb into the crankcase and/or the compression chamber.

[srbaum]

Valmika,
It happened to me and it WAS the fuel pump.
Best regards,
Steve Baum

[Valmika]

Originally Posted by Var Korall

On most 4 stroke outboards, if you lay them down with the wrong side up, the gas will drain through the carb into the crankcase and/or the compression chamber.

This happens while the engine is running in a barrel for less than 10 minutes it puts about 2 oz of fuel into the oil

[Valmika]

Originally Posted by srbaum

Valmika,
It happened to me and it WAS the fuel pump.
Best regards,
Steve Baum

Thanks Steve. We will go back and look at the FP again.

[liquidice]

Originally Posted by Valmika

I have a 2009 Mercury 6hp 4 Stroke. I have gasoline entering my crank case and I don't know why.



I have serviced the carburetor and needle valve and both look good.



I have checked the needle valve with vacuum tester and holds vacuum.



The compression was good.



It's blowing grey smoke even after an oil change. I've done 4 oil changes now to remove all the gas from the crank.



Why is the crank filling with fuel? I am stumped. Any and all advice on how to remedy this problem would be greatly appreciated. Thank you!

Sounds like the symptoms I had with a Honda 7.5 hp that ended up being a cracked head. It started and ran, but when I revved it up, oil escaped. Just a (sad) idea.

[Valmika]

Originally Posted by liquidice

Sounds like the symptoms I had with a Honda 7.5 hp that ended up being a cracked head. It started and ran, but when I revved it up, oil escaped. Just a (sad) idea.

I am trying to think of how a cracked head could put fuel in the crankcase oil. Can you elaborate? We will be checking compression and fuel pump again today.

[Mike Banks]

Sounds like a perforated fuel pump diaphragm.

[Valmika]

Thank You everyone. It looks like it was the fuel pump. It looked intact and I pressure tested it (with my own lungs) and it seemed good but it was not. Thank you all once again.

[a64pilot]

If you have one of those CARB compliment fuel cans that won’t vent, that swell up in the sun etc that can cause it, they won’t vent so they build pressure which can cause the pump diaphragm to tear or it can overwhelm the needle and float and flood the engine that way, if you have one of those cans get into the the habit of disconnecting the fuel line when your not using the motor or get a non compliant can.
They are sold on Amazon.