Gas mixes with oil, and blows through inlet

Hello everyone

My parrents got a simplicity mower with an B&S I/C Gold 13.5hp. It starts and runs, but suddenly it backfires, and a mixture of oil and gas blow out into the airfilter. When I tapped the oil from it, I discovered that there was a lot of gas in it too.
I then checked the floater and needle in the carburettor, wich worked fine and closed off well. Then i thought it might be the oil ring, so I split the engine apart, and the oil ring is perfectley fine. The valves are also closing as they should. Does any of you have an idea why this is happening? I thought it might happen through the crankcase breather, but Im not sure.

Sounds like you have a stuck float in the carb, or a bad needle on the float.

Gee probably all you needed to do was add an inline fuel shut off valve and use it whenever the engine is not running. Of course a new float needle and seat is what will be recommended but shutoff valve is cheap insurance. May as well re-ring it now. IF by chance this mower has a fuel pump on it, the diaphragm may have a hole in it.

You people do check the oil level before operating? And being too high is as bad as being too low.

Walt Conner

As mentioned above, the float needle closes off just fine. The broblem occurs also when I first drain the cylinder (removing the spark plug and cranking it till nothing comes out of it) and then starts it. And yes, the oil level were just below maximum. This is why I am so confused, when everything seems fine.

"As mentioned above, the float needle closes off just fine."

First off, it is not possible for you to know the float is "closing off just fine"

"The broblem occurs also when I first drain the cylinder (removing the spark plug and cranking it till nothing comes out of it) and then starts it."

This is proof that the needle is NOT closing off just fine.

Walt Conner

If I take off the float housing and open the shut off valve, then the gas will run out until i press the float upwards, and then it will stop. This led me to the conklusion that the needle works fine. Am I wrong about that? :ashamed:
What i ment with "The broblem occurs also when I first drain the cylinder (removing the spark plug and cranking it till nothing comes out of it) and then starts it.". Was that it would not help to shut off the gas only when not using it :smile:

The pressure you put on the float to close the inlet is more than the fuel can. This means the needle will not shut off the fuel on it's own. Trying to solve the problem with an in-line shut off is like putting a band aid on the problem. If someone forgets to turn it off when not in use is back to square one. You need to replace both the needle and seat, plus make sure that the float level is set properly. Here is a procedure I use and recommend.


Needle and seat replacement.

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

"Of course a new float needle and seat is what will be recommended but shutoff valve is cheap insurance. "

Ignoring the added safety of an inline shut off valve is foolish advice.

Walt Conner

Thanks a lot Rivets, that makes sense to me. I have a hard time changing bits without knowing exactly why there is a problem. Im only here to learn. I will see if I can find a floatneedle, seat, piston/oil rings, and gasket set in my country. Otherwise can you recommend a online dealer?

Not to be rude Walt, but that isnt even the problem. It does have a shut off valve. But the problem occurs also when the cylinder has been emptied, oil changed, and then started right after (read; the shut off valve should be turned fully on, as if there werent any). I see what you mean about the safety though, and it is of course turned off when not in use.

I have never ordered anything on-line, but Jack's Small Engines has good reviews. You must remember to read my signature, before you follow my advise, as I never recommend a shut off valve, as too many people think they will solve the problem. My students were always taught, doing the job the right way the first time, means you don't need insurance.