Briggs Stratton Experts...........

Goose · May 5, 2019

On another forum, I posted the other day about my wife loaning a neighbor a riding lawn mower. The mower she loaned them is a 42" with an 18.5 single cylinder B&S engine.

The next time my wife wanted to use the unit, the engine wouldn't turn over. I pulled the spark plug and found the cylinder full of gasoline. The crankcase was empty, also. I spun the engine with the spark plug out long enough to clear the cylinder of gasoline. I added oil to the crankcase, put the plug back in, and tried starting it. It would run for a few seconds and die. Smoked like hell while it tried to run. I theorized that the teenager who actually mowed with it had run it the whole time with the choke closed.

I checked it again this afternoon, and the cylinder was full of gas again. I pulled the intake manifold loose, and it was dry inside.

My question is, how the heck can the cylinder be filling with gasoline when the thing is just sitting? I never saw anything like that before.

Does anyone have any ideas?

I

tomturkey · May 5, 2019

Goose, I had a rider that did that. The electric solenoid on the bottom of the carburetor was not shutting off the gasoline as it was designed. I regularly had to pull the plug and spin it over to clear the cylinder of gas. I believe this condition shortened the life of the engine due to the gasoline washdown. I put a manual shut off in the line and the problem was gone, but I believe the damage was done. Don't know if yours has the electric fuel valve but I had a similar experience. gobble

T.R.K. · May 5, 2019

That solenoid is only on the carburetor to stop the flow of fuel through the jet so it doesn't backfire when shut off. It does not keep the engine from filling with fuel as the fuel can still go through the float bowl vent into the intake manifold and from there into the engine. On most Briggs single cylinder engines its a downhill run into the cylinder from there and if the gaskets on the intake and carburetor are pretty good you won't have a clue that anything is going wrong.

The real reason it filled up with gas is the needle valve or the seat it seals to in the carburetor is failing and allowing gas to flow all the time.

If it was like that when your neighbor used it, and he ran it very long at all like that, the rings are probably wiped out and it will always smoke and burn oil from now on, regardless of whether you repair the carburetor to keep it from overflowing again.

UncleTom · May 5, 2019

Does it have the Niki carburetor on it? The seat is aluminum where the float needle seats into.They get worn real early in there life and wont shut the fuel off. And it will over fill the carb and run into the intake valve and fill the cylinder with gas in a short period of time. Then it will fill the crank case too.It will hydraulic the engine to where it wont turn over. I had one given to me. It had like a gallon and a half of fuel and oil in the crank case. Then i pulled the spark plug and turned it over and it shot gas out the plug hole like a stream. I put a fuel shut off valve inline of the fuel line and shut the valve off when done mowing and run the carb dry. lasted 3 years and then i sold it. There is no fix that i know of to that carb. They either came with a Walbro or a Niki. Niki's are junk.

ztrmowers · May 5, 2019

leaks thru carb or if has fuel pump can leak there also or both

Joe W. · May 5, 2019

A few years ago I had the same problem with my lawnmower cylinder filling with gasoline. The lawnmower shop mechanic told me to put a manual shutoff on the gas line and to be sure to shut it off when I was done mowing. I did that and it solved the problem. Same solution as tomturkey said. Oh, and don't forget to turn the gas back on before you start the engine - from someone who knows.

Brian Dan · May 5, 2019

You can do two things to make it stop leaking into the cylinder. One is to put a in line fuel shut off valve on it and shut the fuel off every time you use it. Number two is install a new carburetor. Quit using fuel with ethanol. Ethanol is very hard on the needle valve in the carb.
I think the only thing you did to your engine was give it a good cleaning. Run it and the smoking will quit.
Brian

Brian Dan · May 5, 2019

I ment to say shut the fuel when done using the machine.

Steve@Advance · May 5, 2019

It's either the carb flooding or the fuel pump diaphragm.

If the tank is above the engine, it is gravity flowing into the engine. If below, possibly the tank is pressurizing as the temperature rises.

Did you check the oil again? It may now be over full, diluted with gas.

I would check the pump and the carb. Adding a manual shut off valve would be a good idea just for peace of mind.

But if it was run out of oil, it may be damaged.

Goose · May 5, 2019

Thanks for all the responses.

I suspected the float or needle valve, also. That's why I pulled the intake manifold loose. I expected it to be wet inside from fuel leaking through, but it was bone dry. That's why I'm stumped.

Guess I'll pull the carb apart and check the float and needle valve.

Denny K · May 5, 2019

The Ethanol fuel had nothing to do with your problem

LarrySTN · May 5, 2019

Ethanol does contribute to the problem. The viton tip on the float doesn't like exposure long term, there are other issues that come into play in a humid climate with ethanol mixed gasoline and carbureted engines. My customers that use non ethanol gasoline seem to never have carburetor issues.

buickanddeere · May 5, 2019

. About the same thing as when my stupid arse son was using my tractor . Drove it until it ran out of fuel . Then poured fuel in from a jug hitting all the formerly unreached crevices and low spots in the tank where years of mud, crud and dirt had accumulated .
Plugged everything with the stirred up debris . Several fuel filters plugged and shortly after the low pressure mechanical fuel
Pump failed .
Then yesterday the other boy was phartassing around with the high pressure washer and wrecked it . I expect he let it run for some time without pulling the trigger on the wand . Over heated it probably .

hd6gtom · May 5, 2019

Denny K is right. I run e15 in everything. Chain saw sit for months with e15 in it. Lawn mowers sit all winter with e15 in it and they never have problems starting. If you've got an ethonal problem you have a machine problem. Everything made and imported into the USA after 1986 is supposed to be good to run ethonal. Absolutely no stabil or any of that other mouse pee in any of my machines.

tractorguy2 · May 5, 2019

That is a fairly common problem with B&S engines. The carb runs over and fills the cylinder with gas. Most times also fills the muffler full or oil/gas and makes them smoke for a while. In the old days there was a hole in the carb. if it ran over the gas dripped out on the ground. The good people at the EPA removed the hole. Now when the carb runs over it fills the cylinder and most times the crankcase. I just fixed a craftsman last week with the same problem. Most require a new carburetor.

Will Herring · May 5, 2019

Ugh, seems like an old grubby Ariens we used to have had a similar problem where if you didn't use the fuel shutoff, next thing you know the cylinder would fill with gas. Yuck.

Briggs Stratton Experts...........

Goose

Well-known Member

tomturkey

Well-known Member

T.R.K.

Well-known Member

UncleTom

Well-known Member

ztrmowers

Member

Joe W.

Member

Brian Dan

Member

Brian Dan

Member

Steve@Advance

Well-known Member

Goose

Well-known Member

Denny K

Member

LarrySTN

Member

buickanddeere

Well-known Member

hd6gtom

Well-known Member

tractorguy2

Well-known Member

Will Herring

Well-known Member

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