11hp Briggs and Stratton

11hp B&S, sat over the winter and now the oil smells a lot like gasoline. Also the level is higher than it was in the fall and the fuel tank is now empty.
I know the carb needs to be rebuilt and I have ordered the parts to do so but my question is how would the gas enter the crankcase.
I have my theory which is that there is a bad valve seal. If this sounds reasonable, how difficult is it to replace the seals on the intake valve?

The needle valve under your float is probably leaking gas into the engine. Buy a carb kit that has the new needle valve. It may have dirt under it keeping it from seating. Your valves have nothing to do with gas leaking. Hal

I did order a complete carb rebuild kit which has the parts you describe.
My question is, is this the only reason I would have gas in the oil or is there something else?

Sounds as if something got between the needle & seat & drained the gas tank in to the oil sump. Ceeck the float & make sure that it doesn t leak gas into it. What I do is take the float & tie a lead weight to it & submerge it in fuel for several minutes , then take it out & shake it to see if fuel has seaped into it. If it has fuel in it , get a new float before reinstalling it in the carb. also replace the needle & Seat.

I have a carb rebuild kit on order which includes the inlet needle and seat.
My question is, in a normal 4 cycle engine, how would gasoline get from the intake port to the crank case even if it was poured directly into the port which is most definitely the case because the old needle and seat were worn out?

Time.

Valves and rings are not air tight. In slow motion they seep. Thats way you can turn one over by hand slowly and hear the hissing sound. Over time the gas just flows past the valve into the cylinder, past the rings to the crank case that will hold it.

If the float has a leak, and it doesn't float--the gas will all eventually leak into the crank-case, and if you don't know the correct way to check the oil, you will eventually hear a loud "BANG" and the jig will be up!
Also, a bad needle and seat will allow gas to fill the crankcase.
When checking the oil, after a time of setting, like over night, if you don't do a:"Pull the stick, wipe it, insert the stick, then pull it again, and read it, you will soon hear the "BIG BANG, that will repay you for your ignorance!
That oil will stay at the level on the stick, where it was when you shut it off the last time, and if you just pull it, and read it--you will think there is extra oil in the crank-case, and eventually blow the engine!
I have heard of folks who think there is too much oil in the engine, each time they do the "single stick", and they then drain some out!! They wonder just who is playing tricks on them, by adding oil to the engine when they are not looking, nor around! Sooner or later--they find out who was the dumb one!

(quoted from post at 17:07:16 05/06/11) Time.

Valves and rings are not air tight. In slow motion they seep. Thats way you can turn one over by hand slowly and hear the hissing sound. Over time the gas just flows past the valve into the cylinder, past the rings to the crank case that will hold it.

Click to expand...

Thank you, that was the answer I was looking for. I simply wanted to know if there was anything else that might be wrong. Now I know that once the carburetor is rebuilt and the oil is drained and refilled, I should not have to worry about it. I will probably install a fuel shut off too as an extra measure of protection.

How gas can get into the crankcase of a small engine:

The needle valve does not seal, allowing the float bowl to fill up.

When the float bowl overflows, there are at least 2 ways into the intake port of the carburetor-Through the bowl vent and through the main jet. Most modern carburetors connect the bowl vent to the intake port ahead of the venturi. Older carburetors may have an external vent.

Any fuel in the intake of the engine can flow past an open valve into the combustion chamber, on top of the piston.

fuel also has another path through the crankcase vent, as in most modern small engines the crankcase vent is connected to the carburetor inlet or air filter housing with a hose. Gasoline can take this path even if the intake valve is closed. There is a valve-usually a reed valve in the crankcase ventilation system. Its purpose is to keep a partial vacum in the crankcase, to keep oil from blowing out of the crankcase. But it does not seal tightly enough to keep gasoline out.

fuel in the combustion chamber can go past the rings-remember, there is a gap in each one. And the seal of the rest of the ring surface is not 100%. Then work past the piston skirt into the crankcase.

Definately put the EZ twist fuel shut-off in the line leading to the carb just for safety sake. I install them on all the mowers I service and tell customers to shut off gas when they are finished. I also tell them NOT to fill fuel tank until it's time to use it.

Yup, just ordered a couple of 'em.