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Any idea what would cause a 286707 0441 01 12.5hp to run fine for a minute or so and then start blowing fuel and oil out of the crankcase breather?

Yep once your engine gets warmed up ....... I have seen that before..... Head gasket and a good valve lapping....

Once you lap the valves you will have to adjust the valve lash...... You will need to take the head off then the side plate to expose the valves ...... Then take them out and adjust accordingly.......

Now 1 other thing, you might not need to lap the valves... But you do need to check the clearance of them... If they are in spec then you are in great shape........

Someone else will chime in and either agree with me or give another diagnosis..... So just hold on a bit and see.....

Let us know Mon Ami ~!~!

How is your oil level?
Fuel in crankcase?

I'm not sure, I will change oil tonite and test.

I checked the oil and it is right on the add line just below the hash marks

One of the reasons Mike asked you about the oil level is that the Over Head Valve engines make oil when the head gasket blows or the carb needle and seat leaks....... If you have a fuel pump on your engine and the seat is bad then the vacuum from the crankcase will pull gas from the carb and tank when you shut the engine off..............

I still think you have a bad head gasket.... You have the L Head engine on your mower..... Do you have a compression gauge ??

A leak down tester will tell the story all the way....

Let me know what carb you have......... Plus Tard Mon Ami ~!~!

I'll check compression tonite. Original carb was a walbro. Replaced it with a new one. Problem was still showing up after old carb was replaced. I dont have a leak down tester.

Did you do a comp test ???

Let us know Mon Ami ~!~!

Boudreaux In Eunice La. said:

Did you do a comp test ???

Let us know Mon Ami ~!~!

Click to expand...

Today when I get out of work I will. Hard to do anything when I work 13 hrs a day 7 days a week.

Yes, like Boudreaux says I was wondering about carb flooding since you said blowing fuel & oil out breather hose. You made no mention of fuel in crankcase, so I'm guessing that is a no?

I did the compression test 3 times and all 3 came back at 70 psi. I have no idea what the spec is supposed to be.

pulled the dipstick and found the oil smelled like gasoline also, oil level is on the line just below the hash marks

Because of the automatic decompression there is no compression spec as every 0.0001" variation in the valve lash will change the readings.
If fuel smells like fuel you need to pull the card off and give it a proper cleaning
see http://outdoorpowerinfo.com/ go to the repair section and find your carb.
If there is a lot of debris in the float bowl then tine to replace the fuel filter as well.
If the debris is rubbery feeling then time to replace the fuel lines too.

The thin oil will not make a proper seal behind the rings and cause excessive crank case pressure with blows out the breather tube into the carb / air filter.

bertsmobile1 said:

Because of the automatic decompression there is no compression spec as every 0.0001" variation in the valve lash will change the readings.
If fuel smells like fuel you need to pull the card off and give it a proper cleaning
see http://outdoorpowerinfo.com/ go to the repair section and find your carb.
If there is a lot of debris in the float bowl then tine to replace the fuel filter as well.
If the debris is rubbery feeling then time to replace the fuel lines too.

The thin oil will not make a proper seal behind the rings and cause excessive crank case pressure with blows out the breather tube into the carb / air filter.

Click to expand...

Hi Bert

Carb is brand new, replaced it a week or so ago. Problem existed before new carb was installed.

stangnutlx1 said:

Hi Bert

Carb is brand new, replaced it a week or so ago. Problem existed before new carb was installed.

Click to expand...

Did you replace the oil & filter with the new carb ?

70 PSI is low even with the compression release that is built in on the cam....... You should read at least 90 or higher....

If you can get your hands on a leak down tester or a buddy to do it for you would be a great help.......

I still think you have a leaking valve.... I saw you saying you have a new carb... OEM or china made ??? I don't think a china carb would cause your issue though, because you said the issue was there before you changed the carb......

Let us know Mon Ami ~!~!

Its an OEM Walbro carb. i'll see what I can come up with for a leak down tester.