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So this is the second Briggs flat head that I've had do this. This one is a 10.5 HP Model 28D707 Type 0123-01 Code 960716ZB. Upon a cold startup, it will run for about two minutes, then it starts spitting a gas and oil mixture into the intake from the breather tube coming out of the engine block. Once the engine is warm, it starts spitting immediately upon startup. Of course the engine will not run like this, as it chokes itself out. I set up a test using an empty oil bottle connected to the breather hose (see pic). The engine ran flawlessly while I drove the mower around the yard, as it was spitting into the bottle and not the intake and carb. I then poured the fluid into a clear bottle to see how much came out. The ride was about 2 minutes, and it filled the bottle with about 6 oz of fluid. That is excessive in my opinion. It shouldn't spit out any fluid, correct? So what causes this and how hard is the repair? It seems like a shame to have an engine running this well to basically get choked out by itself. By the way, I never did figure out the previous engine that did this, I ended up selling it as-is.

My preliminary research here on the site is indicating a possible blown head gasket. Can anyone confirm or deny this? I'm fairly certain it's not a carburetor issue, as the engine runs flawlessly when the breather tube is taken away from the engine.

You are getting way too much crankcase pressure. Yes a head gasket will do that or a bad piston.

reynoldston said:

You are getting way too much crankcase pressure. Yes a head gasket will do that or a bad piston.

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Thanks for the response. What do you mean by 'bad piston'? I would think that would cause less pressure in the crankcase...

No mention was made about oil level. Crankcase full of gasoline will do it also and much more common than blown head gasket on flat head B&S.

Walt Conner

Tinkerer200 said:

No mention was made about oil level. Crankcase full of gasoline will do it also and much more common than blown head gasket on flat head B&S.

Walt Conner

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Yes I agree, always good for more ideas.



Bad Piston , compression going from the top of the piston into the crankcase making crankcase pressure, can be anywhere form a hole in the piston, bad cylinder walls, worn out rings. Start with Tinkerer's idea first, over filled with oil because you did say it ran good. Piston would be the last thing to check. A good test for the piston is called a leak down test.

Tinkerer200 said:

No mention was made about oil level. Crankcase full of gasoline will do it also and much more common than blown head gasket on flat head B&S.

Walt Conner

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Crankcase is indeed full of gasoline, more gas than oil as a matter of fact. Is this the needle and seat causing this?

reynoldston said:

Yes I agree, always good for more ideas.



Bad Piston , compression going from the top of the piston into the crankcase making crankcase pressure, can be anywhere form a hole in the piston, bad cylinder walls, worn out rings. Start with Tinkerer's idea first, over filled with oil because you did say it ran good. Piston would be the last thing to check. A good test for the piston is called a leak down test.

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I gotcha, that makes sense.
I've heard of a leak down test, but never performed one myself.

jakesmurray said:

Crankcase is indeed full of gasoline, more gas than oil as a matter of fact. Is this the needle and seat causing this?

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Yes it is not closing to shut off gas flow.
I could tell it had gas in the oil in picture 1.

BlazNT said:

Yes it is not closing to shut off gas flow.
I could tell it had gas in the oil in picture 1.

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I could test this by removing the bowl and pushing up on the float to see if it stops flow, correct?

Also, here is a thought. Could I hook my little bottle up to the engine again, then once it spits all of the extra fuel/oil it should run correctly with the breather tube hooked up right? Or I could pull the drain plug and take out the extra fluid I guess...

The fuel thins out the oil. Drain the oil out.

Mikel1 said:

The fuel thins out the oil. Drain the oil out.

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Ok, yeah it's about the consistency of gasoline now...

Not really. You have more power than the gas. A better test is to turn it upside down and blow into the fuel inlet. If you cant blow then its working.

BlazNT said:

Not really. You have more power than the gas. A better test is to turn it upside down and blow into the fuel inlet. If you cant blow then its working.

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Ahh, never thought of that. Stuff like this is why I love forums.

I'll update this thread when I get to look at this thing.