The gasoline line from the gas tank to the carburetor in my riding
mower has no shutoff valve. It is a carbureted engine.

This week I filled the tank in the riding mower. Later the same day, I
noticed a gasoline smell in the garage, and traced it down to the
mower. It was dripping gasoline out the exhaust! The engine hadn't
been run in more than a week. The gasoline level in the tank had
dropped about a quart!!

The only way I can figure that gasoline could get from the tank to the
exhaust is through the float valve in the carb. Do most inexpensive
carbureted riding mowers nowadays have a float valve in the carb and no
shutoff valve in the gas line??

yes
Ether Jones wrote:
The gasoline line from the gas tank to the carburetor in my riding
mower has no shutoff valve. It is a carbureted engine.

This week I filled the tank in the riding mower. Later the same day, I
noticed a gasoline smell in the garage, and traced it down to the
mower. It was dripping gasoline out the exhaust! The engine hadn't
been run in more than a week. The gasoline level in the tank had
dropped about a quart!!

The only way I can figure that gasoline could get from the tank to the
exhaust is through the float valve in the carb. Do most inexpensive
carbureted riding mowers nowadays have a float valve in the carb and no
shutoff valve in the gas line??

Ether Jones wrote
The only way I can figure that gasoline could get from the tank to the
exhaust is through the float valve in the carb. Do most inexpensive
carbureted riding mowers nowadays have a float valve in the carb and no
shutoff valve in the gas line??

------------

Yes.

You didn't ask, but a common cause for your problem is a
small bit of debris holding the float valve open. The cure is
a simple cleaning. The prevention is to be extremely careful
to get gasoline and only gasoline into the fuel tank when
refueling. It doesn't take much of a bit of grass clipping,
dust, dirt, etc. to cause a problem.

Gideon wrote:
Ether Jones wrote
The only way I can figure that gasoline could get from the tank to the
exhaust is through the float valve in the carb. Do most inexpensive
carbureted riding mowers nowadays have a float valve in the carb and no
shutoff valve in the gas line??

------------

Yes.

You didn't ask, but a common cause for your problem is a
small bit of debris holding the float valve open. The cure is
a simple cleaning. The prevention is to be extremely careful
to get gasoline and only gasoline into the fuel tank when
refueling. It doesn't take much of a bit of grass clipping,
dust, dirt, etc. to cause a problem.

There's a filter in the gas line from the gas tank to the carb.
Although I am extremely careful about cleanliness when filling the gas
tank, I doubt if any debris in the tank large enough to cause a problem
in the carb could ever get past that filter.

I changed the gas line and gas filter two years ago. I spent an hour
cleaning the gas line fittings with a toothpick and toothbrush and
Q-tips and vacuum before removing the gas line, to make sure no debris
got into the fittings. I inspected the new gas line before installing
and noticed it had manufacturing debris inside it! I washed it out
with fresh gasoline before installing. I'm pretty sure there is no
debris in the carb.

I had a friend who took his riding mower to the place of purchase for a
"tune up". Among other things, they replaced the gas line and gas
filter. His mower hasn't run right since. I told him some high school
kid probably replaced the gas line and got debris in there that found
its way to the carb.

Back to the gas leak: In my case, I had run the mower out of gas and
it sat that way for a week before I filled the tank with fresh gas. A
couple of hours later I noticed the leak. I NEVER run the carb dry
on this engine; this was a one-time aberration. I'm convinced there
is a direct correlation between running the carb dry, and the leak. I
have the service manual for the engine but it gives no details about
the float valve design. I stopped the leak by tapping lightly on both
sides of the carb with a piece of iron rebar.

Has anyone else ever experienced this sort of problem? What's the
street wisdom on fuel additives for cleaning the float valve?

The engine is a 4-cycle Briggs 16.5HP L-Head opposed twin. Does anyone
know if the float valve seal is brass, or some sort of elastomer?

Ether Jones wrote:
Has anyone else ever experienced this sort of problem? What's the
street wisdom on fuel additives for cleaning the float valve?

My single experience with additives : they clog the carburetor by
dissolving crud that lines the fuel system, if you use it on an old
engine.

I've been using stabil with a Honda generator from the beginning, and
borrowed some of that fuel for the ancient lawnmower. The lawnmower ran fine
for about an hour and a half and then started missing, and hasn't run right
since.

The Honda works fine.

So I'm guessing cleaners aren't a great idea in old fuel systems. Odds are.

--
Ron Hardin


On the internet, nobody knows you're a jerk.

Ron Hardin wrote:
for about an hour and a half and then started missing, and hasn't run right
since.

Incidentally, if anybody knows if there's a mixture control on a Briggs
and Stratton 4 hp push lawnmower engine, if you start taking things off,
let me know. I think it can be fixed by leaning out the mixture, as it
runs great when it's just about out of gas. I see no signs of an adjusting
screw.

--
Ron Hardin


On the internet, nobody knows you're a jerk.

Ron Hardin wrote:
Ron Hardin wrote:
for about an hour and a half and then started missing, and hasn't run right
since.

Incidentally, if anybody knows if there's a mixture control on a Briggs
and Stratton 4 hp push lawnmower engine, if you start taking things off,
let me know. I think it can be fixed by leaning out the mixture, as it
runs great when it's just about out of gas. I see no signs of an adjusting
screw.

If you were to bend the lever on the float so as to lower the gasoline
level in the bowl, would that make the jets run a bit leaner?

I have a vague recollection of doing that back in the '70s on a
motorcycle engine carb.

Ron Hardin wrote:

I've been using stabil with a Honda generator from the beginning, and
borrowed some of that fuel for the ancient lawnmower. The lawnmower ran fine
for about an hour and a half and then started missing, and hasn't run right
since.

I use StaBil in all my small gas engines over the winter.

It was my understanding that StaBil merely keeps the gas from forming
varnish. I was not aware that it had any solvents/detergents for
dissolving existing varnish deposits.

On 3 Sep 2006 12:46:15 -0700, Ether Jones wrote:
Back to the gas leak: In my case, I had run the mower out of gas and
it sat that way for a week before I filled the tank with fresh gas. A
couple of hours later I noticed the leak. I NEVER run the carb dry
on this engine; this was a one-time aberration. I'm convinced there
is a direct correlation between running the carb dry, and the leak. I

Given your described cleanliness, I suspect running the carb dry did
cause the float to stick. The little bit of gasoline left in the system
after the engine quit evaporated, leaving behind a bit of sticky gum or
varnish. The float was all the way down (opening the valve) and there
it stuck when you filled the tank.

I highly recommend stabil. It prevents (or nearly so) that sticky
residue from evaporating fuel.

In equipment I use frequently I typically do not use stabil. But in my
chipper, the generator and every 2-cycle engine I always use stabil. In
the lawn mower I start using stabil in the fall as I never know which
cutting will be the last. And I try to keep the fuel tanks full (and if
there is a shutoff valve, I close it, just in case).

I'm going to try Pri-G this winter... It is a lot cheaper than stabil.

sdb

--
Wanted: Omnibook 800 & accessories, cheap, working or not
sdbuse1 on mailhost bigfoot.com