Let us not put the cart before the horse! What is most likely happening (in the proper sequence) is this. It sounds like your crankcase is being "flooded" with gasoline due to an intermittent leakage of fuel past the needle valve in the carburetor fuel inlet. I say "intermittent" because of the varying run times required for the symptoms to appear. What happens in this case is, fuel leaks past the needle valve and overfills the carburetor (when engine is not running). Fuel can then leak into the intake and flow into the cylinder where it will then leak past the piston rings and into the crankcase, mixing with the oil. Next time you run the engine and the oil warms up, the gasoline begins to vaporize out of the oil and this additional "fuel" then flows from the crankcase breather right back into the intake. You have been thinking that "When this happens it fills the crank case full of gas." The reality is that the crankcase is already contaminated with gas and when that gas vaporizes from heat, it fills the intake with gasoline vapors which will prevent enough AIR from being drawn in through the air filter to support combustion. The net effect is that the material entering the combustion chamber is too full of fuel and too deficient of air to combust. Engine chokes and dies. Install and use an inline fuel shutoff valve and the problem should disappear.

Thanks.
Would that also be the reason it seems to lock up when I try starting it before the oil/gas change?

Yes, that is likely. It is called "hydrostatic lock" when the cylinder is at least partially filled with liquid. This usually occurs when the engine stops with the intake valve closed and the gas leak fills up the intake. Some of this gas leaks past the intake valve and enters the combustion chamber (but very slowly). Most of the gas will leak out the carb throat and air filter housing (after filling the intake). The gasoline that leaks past the intake valve will all leak past the piston rings and into the crankcase (where it mixes with the lube oil). If the intake is full of gas when you try to crank the engine, this "liquid slug" will be drawn into the cylinder when the intake valve opens. As the piston next moves upward on the compression stroke (piston movement TOWARD the head is always referred to as "UP", even if the cylinder is horizontal or even upside down) it will reach a point where the pressure in the cylinder is too great for the piston to move (because liquids are "incompressible") and the starter will "stall". The pressure developed can bend connecting rods and crankshafts under certain conditions. These "certain conditions" do not usually occur if you are using the starter motor or pull rope. If it is a vehicle with a "gear type" transmission (motorcycle for example) that is being "push started" or "roll started", serious damage may be done. If the intake valve is open when the engine stops, the leakage can fill the crankcase with the entire contents of the fuel tank and might not leak any gas out on the ground. If this engine is one of the type that needs periodic valve adjustment to maintain the effectivness of the compression release feature, that could be a reason that the engine seems to "lock up" when you are trying to start it. Post the engine model number and type number from the engine and of the Briggs experts here can confirm or dispute whether your engine is in that group. My guess is "hydrostatic lock" is what you observe.

Hi again,
Model 28P777
Type 0641 A1
Code 9512204B
So far, you've got it nailed!
So what about this electric fuel shut off? Other than the needle, how does it fit in to the equation if at all?
The best place to install a manual S/O would Be?

Thanks again,
If you've got any Qs about woodworking or staircase construction, let me know!

Gary

The "electric fuel shutoff solenoid" is on there to prevent/minimize AFTERFIRE (a.k.a. "backfire") when shutting the engine down. The fuel solenoid closes the plunger valve when the key switch is turned to OFF. The fuel solenoid stops the flow of fuel through the MAIN JET only. There are 2 jets in these carbs. The PILOT JET serves to provide a very small volume of fuel for extremely low RPM (such as idling and slightly faster RPM). The MAIN JET provides the greater volume of fuel needed for high RPM and heavy loading of the engine. During the mid range of RPM, the pilot jet and idle jet both contribute a "fair share" of fuel to the mix. At high RPM and heavy loading, the amount of fuel provided by the pilot circuit can almost be insignificant. As mentioned, the fuel solenoid is there to stop (or reduce) "afterfire" on shut down. The recommended way to shut down engines that have a fuel solenoid is to turn off the key switch while the engine is running at a high RPM. Turning off the key takes away the 12VDC from the fuel solenoid but has no effect on the ignition system. The ignition system keeps on sparking away, burning off any residual fuel AND purging the intake, combustion chamber, and exhaust with almost 100% air. The tiny amount of fuel provided by the pilot jet will not allow the engine to keep running during the "winding down" period because the throttle plate (a.k.a. "butterfly") is open wide, which makes the mix too lean for the engine to run on. The reason the fuel solenoid cannot serve as a fuel system shutoff valve is because it seals only the main jet. The pilot jet is still open to allow gas to pass through it and flood the engine if the needle valve is not cutting off the fuel like it is supposed to. The best location to situate your inline shutoff valve is between the carburetor and the fuel tank (if gravity fed), or between the fuel pump and the fuel tank (if pump fed).

Oh, another thing. Gasoline in the crankcase can "shut down" an engine that uses a "pulse operated" fuel pump by creating a positive pressure in the crankcase when the gas begins to "boil out" of the oil. If the pressure of the vapor is great enough to "hold" the pump diaphragm in the "pressure pulse" (occurs when piston moves downward) position, the fuel pump will stop pumping until the crankcase pressure drops enough to allow a "vacuum pulse" to be created when the piston moves upward. It is the alternating "pressure-vacuum-pressure-vacuum" pulses that provide the motive power that these fuel pumps operate on.

Gee, Mownie, you have just explained a lot of things to all of us, and cleared up any confusion that might have ocurred, about those problems!
I might add this: If somebody installs a different engine in a tractor with a carburetor fuel inlet that is higher than the under-seat fuel tank outlet, they will have to install a fuel pump! And, sometimes the problem of where to install the vacuum line comes up. After much trial and error, i solved my problem by drilling a hole near the top of the dip-stick tube, inserting a brass fitting in that hole, then running the hose to the carb inlet. Before that, i had spent a considerable amount of time trying to adapt the line to the crankcase breather, with no success. Thanks for the info! by: Rusty Jones

The part that bothers me about this story is the first carb is replaced and the problem goes away temporarily. Only to end up with the same random problem ...

At this point - the way I see it is your problem is up stream. I wonder - when you swapped carbs, did you by chance refresh your fuel lines along with a new fuel filter?

My thoughts are that perhaps you have a deteriorating fuel line which was randomly introducing debris into the carb. Once you swapped out the carb it ran for a bit until the new carb becomes ill - due to deteriorating fuel line. Or perhaps a filthy fuel tank with no filter on the line ?

Just a though.

Good luck - Dave

Hi Dave
Me Too. Although I rebuilt the carburator, the replacement that I paid for and was told happened, was someone elses doing. I hope the guy didn't bag me.
At this point I don't care as long as I get it fixed But, He will be getting a call.
Anyway for what it costs to replace lines, I might as well do that too.
Thanks again
Gary

Well i dont think he bagged you - but let me ask - did this machine have a gas filter.... Seems like som much equipment has come off the line without one ...

If you never had a gas line on the unit - I think most would agree this would be a priority to to address first - then clean out that carb - I use guitar wire - my friend likes to use welding tip cleaners (says their a bit like a file), helps to get at the tough corrosion areas more easily...

Good luck

Good info there njdpo. Now, am I the only one that seems to find a mistake in my postings, even though I try to "proof read" carefully? It probably don't matter but I posted, "During the mid range of RPM, the pilot jet and idle jet both contribute a "fair share" of fuel to the mix." Well.......it should have read "PILOT JET and MAIN JET". The pilot jet and idle jet are essentially the same thing with more than one name throughout the industry. Me goof.

Hello there Mownie - apparently I need to do some proof reading my self...

"If you never had a gas LINE on the unit"

what I meant to say was ...

" If you never had a gas FILTER on the unit... "

Anyway - good luck, chin up, spring is here...

Dave

Check the first two words of my original post.

Glad it ain't just me. Gettin' old sure ain't how I imagined it when I was six years of age. :^)

in addition to the crankcase filling with fuel. I have a fuel shut installed, when I first start it runs good for a minute then the chugging and cauphing start. But when I shut the fuel off it starts to immediately run perfect, until of coarse it runs out of fuel.any ideas ?