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Small Engine Question

My lawn tractor has a 15hp Briggs and Stratton engine that was sputtering and running way too rich. I took off the air cleaner and the air cleaner was a bit dirty but not clogged with dirt, it was clogged mainly with gasoline, and there was some liquid gas in the throat of the carb. Engine runs fine with no air cleaner on it. I went ahead and put on a new, clean and dry air cleaner, and the engine runs fine with it on, but I wonder, what is the cause of all the gas getting into the carb?

It could be a sticky or malfunctioning float.

The carb should be disassembled as much as possible and all of the parts cleaned with carb cleaner.
Better yet, get a rebuild kit.

This carb question is really similar to questions on scooter and motorcycle forums, because they still have carburetors. Anyway, it sounds like you have sediment stuck in the float bowl valve, and the fuel is not getting shut off when the float bowl is full. If you are not going to tear into this yourself, then a shop can fix it, but first I suggest you get a product called “Seafoam” or, if thats not available, a good carb and fuel injector cleaner from a car parts store and add it to your gas. You only need a small amount, because your tank is small. A couple of ounces to 2 gallons.

thx will start with sea foam

Start the engine and attempt to install the screw which holds the filter on… JUST THE SCREW.

Either that filter was more clogged than you thought, the mixture is off, or the RPM governor is adjusted incorrectly.

Well, I have the Sea Foam in the gas tank now, a new air (and fuel) filter installed, and the thing is running fine. We’ll see if the air filter clogs with gas again. For now it is fine.

The interesting thing is, come to think of it, and maybe it is was just a coincidence, but I started having these problems right after I had the tractor tipped up on its back to clear some rope out of the blades that my son ran over while mowing and got fouled in the blades. Immediately after I put the tractor back down and started it up, the engine ran rough and spewed out HUGE amounts of smoke.

The smoke disippated after about 20 minutes, but the engine ran progresively more poorly until I found the problem with the gas-clogged air filter.

Aha, the full story finally comes out!

Gas came out of the float bowl and soaked the air filter. Makes sense now.

I thought of the possibility of the motor being tipped on its side. Yes, the fuel bowl will drain into the intake system and sometime even the fuel from the tank fill run in, on various models. I bet it took a lot of cranking to get the engine to start after you set it down as you probably flooded it badly. Another thing that happens when a B&S motor is tipped the wrong way is that the crankcase oil will drain into the intake system which is the reason for the clouds of smoke. A mixture of oil and gasoline was probably on the air filter and in the carburator throat as pure gasoline would evaporate quickly when the engine ran again.

You should be okey with the new air filter but check the oil level to make sure it is not too low.

Hmmm. Is there a way to avoid this problem next time I have to tip the tractor to service/fix something on the underside? I guess one thing to do is empty the gas tank and then run the engine dry of gas. But what about the oil? If I emptied the crankcase, is it possible residual oil could still get into the intake? I normally don’t have to tip the tractor up unless I am changing the drivebelt or extracting something my son has run over. It would have been much, much harder to get all that tightly tangled rope out of the blades and housing if I had had to put the tractor up on blocks and get underneath it.

Is there a fuel shutoff valve near the carb? Close it off and run the engine until the carb is empty.

It’s not gas on your filter, it’s oil. I’ve seen several cases of the same thing. In some engines, the crankcase breathes into the intake. If you tip the thing, oil comes out and soaks the filter. It will not evaporate readily so it acts as a plug in the air intake, particularly if you have a paper filter element. The engine draws a vacuum. If there is a plug in the air intake the vacuum will draw much more fuel from the carb completely flooding it all the time. Gas is not a problem on the filter because it will just evaporate and burn in the engine.

Looks like researcher got the oil part already. Easy way to prevent the problem when tipping is just take off the filter before you tip it. After you are done, put it back on and be sure and check the oil level to make sure you haven’t lost too much.

there may well have been some oil in it, but there waqs plenty of gas, too. but the thing was soaked in and reeked of gas.

but your tip is well taken, I will be sure to remove the filter before tipping up the mower for service.