Mower engine problem
 

I have a 3.5 hp B&S "classic" engine. While mowing, it started sputtering
and surging like it was about to run out of gas but it has plenty. It does
this in any throttle position. I took off the carb and cleaned the strainer.
It had some junk, but wasn't very dirty. After I put the carb back on, it
ran fine for 3 minutes then started surging again. One thing I noticed is
that it will run smooth seconds before it runs out of gas. Sounds like a
carb problem, but I'm not sure.

Thanks for any help.
John

JohnR66 wrote:

I have a 3.5 hp B&S "classic" engine. While mowing, it started sputtering
and surging like it was about to run out of gas but it has plenty. It does
this in any throttle position. I took off the carb and cleaned the strainer.
It had some junk, but wasn't very dirty. After I put the carb back on, it
ran fine for 3 minutes then started surging again. One thing I noticed is
that it will run smooth seconds before it runs out of gas. Sounds like a
carb problem, but I'm not sure.

Thanks for any help.
John



You didn't mention checking the air cleaner. Did you? If not, maybe it's
gunked up and "choking" the engine? Try running it for a bit with the
air cleaner removed.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

Sounds to me like the gas cap isn't vented correctly either the holes are
plugged or you replaced the cap with a non vented cap. What happens is
everything is fine for a few minutes then the engine quits you wait five
minutes (the vacuum in the tank has equalized by then) and then it will run
fine for a few minutes then repeat. Try unscrewing the cap a little so that
it doesn't pull a vacuum on the tank to eliminate this as a possible cause.

Good luck, Rich


"JohnR66" wrote in message
...
I have a 3.5 hp B&S "classic" engine. While mowing, it started sputtering
and surging like it was about to run out of gas but it has plenty. It does
this in any throttle position. I took off the carb and cleaned the
strainer.
It had some junk, but wasn't very dirty. After I put the carb back on, it
ran fine for 3 minutes then started surging again. One thing I noticed is
that it will run smooth seconds before it runs out of gas. Sounds like a
carb problem, but I'm not sure.

Thanks for any help.
John

"Rich" wrote in message
g.com...
Sounds to me like the gas cap isn't vented correctly either the holes are
plugged or you replaced the cap with a non vented cap. What happens is
everything is fine for a few minutes then the engine quits you wait five
minutes (the vacuum in the tank has equalized by then) and then it will
run
fine for a few minutes then repeat. Try unscrewing the cap a little so
that
it doesn't pull a vacuum on the tank to eliminate this as a possible
cause.


It could be the cap vent is stopped up. Last year a fellow at work had a
mower that would run for a short time and quit and repeat. I told him to
check the cap. He found he had swapped the cap from the can he filled the
mower with the one on the mower tank.. The filling can lid was not vented so
it gave the same effect as you describe.

"JohnR66" wrote in message
...
I have a 3.5 hp B&S "classic" engine. While mowing, it started sputtering
and surging like it was about to run out of gas but it has plenty. It does
this in any throttle position. I took off the carb and cleaned the
strainer.
It had some junk, but wasn't very dirty. After I put the carb back on, it
ran fine for 3 minutes then started surging again. One thing I noticed is
that it will run smooth seconds before it runs out of gas. Sounds like a
carb problem, but I'm not sure.

Thanks for any help.
John


Thanks for the replies so far. I failed to mention that I ran it with the
air cleaner off and had the same result. After reading the posts about the
gas cap, I checked and can see that the holes are not plugged. I should
mention that the carburator is the type with the priming bulb. The
carburator appears to be molded out of nylon plastic and bolts to the gas
tank with 5 screws.
John

the rubber gasket between the carb and the tank is called a diaphram.
it pumps fuel up to the carb, try putting in a new diaphram and that
should fix it. if your primer bulb is the least bit deteriorated replace
it also. ..... in some cases, the tube that the carb slides onto gets
loose or blows the gasket where it attaches to the engine block, that
little gasket cost little but can cause problems if bad... also snug up
the head bolts,the ones by the ex tend to loosen... good preventative
maintenance is to take off the sheetmetal and clean the grass out of the
cooling fins, this is a good time to check the intake tube and gasket...
lucas

forgot to say, change the air filter. i dont think your carb is
designed to work with the air filter bolt out. lucas

On Tue, 31 May 2005 22:52:42 GMT, "JohnR66" wrote:

I have a 3.5 hp B&S "classic" engine. While mowing, it started sputtering
and surging like it was about to run out of gas but it has plenty. It does
this in any throttle position. I took off the carb and cleaned the strainer.
It had some junk, but wasn't very dirty. After I put the carb back on, it
ran fine for 3 minutes then started surging again. One thing I noticed is
that it will run smooth seconds before it runs out of gas. Sounds like a
carb problem, but I'm not sure.

Thanks for any help.
John


Although there are other possibilities, you might also check to see if
the head gasket is leaking. I had a mower with similar problems and
when I happened t o pass my hand past the side of the engine I felt
this hot blast coming from the gasket. Replaced it and the engine
worked fine.
Gary Dyrkacz

Radio Control Aircraft/Paintball Physics/Paintball for 40+
http://home.comcast.net/~dyrgcmn/