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I have a MTD Yard Machine with a Briggs and Stratton 18 hp Twin oppose cylinder Model 42A707.

I have rebuilt carberator with new jets, needle valve, and cleaned. The problem is that it floods out as soon as I try to turn it over. Gas shoots out over the top of the top of carberator and dumping a lot of fuel down the intake.

I can start it cold with the throttle wide open but as soon as I try to back it down it quits, floods out.

I have called a lawn mower/small engine expert in the area and he doesn't have a clue. Does anyone know something I can try. It's got to be something simple I would think and I'm just not getting it. :confused2:
Thanks for any help, The Duckster

It's kind of hard to diagnosis with the info you provided. 1rst I would check your crankcase oil and see if it is overfilled. (maybe even fuel in the oil) If fuel gushes out of the carb, it "could" mean a stuck intake valve. If an intake valve is stuck, the compression has nowhere to go except out the carb throat forcing out any fuel that the other cyl might have sucked in.

Thank you for your response. First of all there is no fuel in the oil, changed it. Also it is not overfilled, I checked. I have a compression tester and it's not that, it maintained the proper level. I appreciated your input, I need another head in this for input. The guy I talked to locally said it's got to be something simple but he can't check it for two weeks. I have a 1/2 acre I need to mow... :smile:
Thanks again, Duckster

I know that this may sound stupid, but I would to raise the float level. Have the float pointing up and bend the tang so that you will reduce the fuel level in the float bowl when the carb is reinstalled.

You didn't happen to get the air cleaner mounting gasket on wrong. If turned incorrectly it will block the carb bowl vent causing flooding like you describe.

Take the air filter off and look for a small hole around the edge of the carb intake and see if you can see through the gasket into the carb. The hole is about 3/16 in in diameter.

Rivets said:

I know that this may sound stupid, but I would to raise the float level. Have the float pointing up and bend the tang so that you will reduce the fuel level in the float bowl when the carb is reinstalled.

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Thank you for the thought but it's a plastic non adjustable float.

IL makes a good point about the vent and gasket. I would also check the gasket between the carb halves.

ILENGINE said:

You didn't happen to get the air cleaner mounting gasket on wrong. If turned incorrectly it will block the carb bowl vent causing flooding like you describe.

Take the air filter off and look for a small hole around the edge of the carb intake and see if you can see through the gasket into the carb. The hole is about 3/16 in in diameter.

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The model number is 42A707, it's not the model you're thinking it is. It can run without the air cleaner on it. Maybe if you can find something on this model? It's approx. a 2002 model MD tractor that I bought used. Thanks so much for your input or anything you can find out.

From the parts breakdown for that engine, which is the engine I was thinking about, it shows that it takes the oblong air filter. The gasket that I am refering to is the gasket between the carb and the air cleaner mount. If you get the gasket upside down or turned incorrectly, the engine will flood

ILENGINE said:

From the parts breakdown for that engine, which is the engine I was thinking about, it shows that it takes the oblong air filter. The gasket that I am refering to is the gasket between the carb and the air cleaner mount. If you get the gasket upside down or turned incorrectly, the engine will flood

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So are you telling me that this cannot run without the air cleaner? I have never seen any gas engine that can't run without the air cleaner, this would be the first and I'm 66. I really appreciate your input. Let me know, thanks.

I was assuming that after the carb repair you installed the air cleaner base plate to the carb. If it is doing the flooding without the air cleaner base plate attached to the carb, then I would look at either the gasket between the two halves of the carb, or the needle valve isn't sealing. also make sure that the float isn't full of gas.

ILENGINE said:

also make sure that the float isn't full of gas.

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Good point! This has thrown me more times than I can remember

ILENGINE said:

I was assuming that after the carb repair you installed the air cleaner base plate to the carb. If it is doing the flooding without the air cleaner base plate attached to the carb, then I would look at either the gasket between the two halves of the carb, or the needle valve isn't sealing. also make sure that the float isn't full of gas.

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I changed gasket between top and bottom of carb and checked float and no gas in it. I changed fuel pump diaphram and gaskets. Drained oil as crank case was full of gas. iIm getting fuel threw hole on top of carb. Looking at engine from front its on choke cable side? I checked needle valve and no groves or damage. I watched video on u tube which is great on how to rebuild this carb and followed instructions and still can't get it to run. I really feel stupid. Thanks for any help. Jim S P.S. I used to live in Mokena and eat at that great steak house on the corner at the center of town.

I'm confused after rereading this entire thread. You say that the model number is 42A707. When I look that engine up it should have a brass float that is adjustable. When you took the carb apart for cleaning, did you replace the float needle and seat? The float needle may look good, but more times than I care to count looks can be very decieving. I would replace the needle and seat with this kit #394682. I have included a service manual for your engine which may help you.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/02_271172TwinCylinderLHead.pdf

Has your needle valve been jammed open.

I know how "Misery Loves Company" and I'll chime in with a similar problem with a 17.5 Single Cylinder Kohler on a Craftsman rider that would do the same thing. Last week I wound up putting a fuel line shut off valve on it so the owner could keep it from flooding out after it sat for a while. I checked the float and needle operation and worked fine, but let it sit overnight or a few days and it would flood the cylinder as well as above the bowl, into the carburetor throat, and up into the filter. I could see a puddle of fuel with the air filter off! I drained a teacup of gas when I removed the carburetor bowl. About that much blown out of the cylinder when I took the soaked plug out! Also blew out about a 1/4 teacup of gas out of the muffler! Now it decided to go to the extreme opposite and not get any fuel at all once the shut off valve was turned on! We'll have to put a carburetor kit in it as it just won't cooperate and hope for the best. It too has a plastic "Non-Adjustable" float. Doesn't give a guy any room to adjust anything out. These non-adjustable plastic floats are aggravating when a little adjustment on the float level would clear things up. Looks like you have a "Problem Child Mower" on your hands!

mrduck said:

I have a MTD Yard Machine with a Briggs and Stratton 18 hp Twin oppose cylinder Model 42A707.

I have rebuilt carberator with new jets, needle valve, and cleaned. The problem is that it floods out as soon as I try to turn it over. Gas shoots out over the top of the top of carberator and dumping a lot of fuel down the intake.

I can start it cold with the throttle wide open but as soon as I try to back it down it quits, floods out.

I have called a lawn mower/small engine expert in the area and he doesn't have a clue. Does anyone know something I can try. It's got to be something simple I would think and I'm just not getting it. :confused2:
Thanks for any help, The Duckster

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Did you get this fixed??

mrduck said:

So are you telling me that this cannot run without the air cleaner? I have never seen any gas engine that can't run without the air cleaner, this would be the first and I'm 66. I really appreciate your input. Let me know, thanks.

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That is not at all what he is telling you ALTHOUGH, B&S says the filter needs to be on for this engine to run correctly. I have never concerned myself about whether it was on or not.

I do not see where you said it runs the same with and without the air filter. Listen to these gentlemen, they are trying to help you. As a youngster you have a lot to learn. I am 84 and still learning.

Since this engine relieves some compression when starting via the Intake Valves, it does naturally blow some out the carb but not to the extent you are experiencing.

Walt Conner

mrduck said:

I have a MTD Yard Machine with a Briggs and Stratton 18 hp Twin oppose cylinder Model 42A707.

I have rebuilt carberator with new jets, needle valve, and cleaned. The problem is that it floods out as soon as I try to turn it over. Gas shoots out over the top of the top of carberator and dumping a lot of fuel down the intake.

I can start it cold with the throttle wide open but as soon as I try to back it down it quits, floods out.

I have called a lawn mower/small engine expert in the area and he doesn't have a clue. Does anyone know something I can try. It's got to be something simple I would think and I'm just not getting it. :confused2:
Thanks for any help, The Duckster

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I know it's late but it might help someone else out water in the fuel weak fuel watered down

Did this ever get solved? I have a splitter doing the same thing

Wild Wild Wes said:

I know it's late but it might help someone else out water in the fuel weak fuel watered down

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