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Briggs & Stratton engine not running smoothly



 
 
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  #1  
Old 05-05-2009, 08:30 AM
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First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default Briggs & Stratton engine not running smoothly

Hi everyone,

My first post on this forum, so a brief intro: we're Brits living in northern France (Normandy) for the last four years, though hoping to return to the UK in the new few months.

I have a mower with a Briggs and Stratton XP40 mower which is not running well. This will be only its third year of use, and I've never had a problem with it until now. I used it for the first time this year a few weeks ago no problem, seemed to be running as normal. I then got it out again last week and found that it wasn't running smoothly. I would say the engine seems to be "hunting" almost like it's coughing slightly it sounds at various points as though it's going to die but always manages to keep going. Two further symptoms: (1) puffs of black smoke are visible by the grill on the L/H side, and (2) it used an awful lot more petrol than usual when I cut the grass with it the other day.

I'm no mechanic, but have done my best to do the basics in an attempt to rule out obvious causes: I've cleaned the air filter (seems fine), taken off the plastic engine cover and cleaned round everything I can, and changed the oil. Doesn't seem to have made any difference.

One other thing I've noticed: when first starting the engine (even after only a few minutes' break in running), it seems to run nice and smoothly for maybe ten seconds or so before starting to cough and splutter again.

I would have taken it in for repair, but there's only one place in the vicinity and they have a 3 week wait! I'd be very grateful if anyone has any ideas or suggestions. (N.B. I've looked on the B&S site, but so far only found quite generic advice that hasn't helped me.)

Thanks in advance,

Rob
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  #2  
Old 05-05-2009, 10:07 AM posted to uk.rec.gardening
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Posts: 777
Default Briggs & Stratton engine not running smoothly


"robinfrance" wrote in message
...

Hi everyone,

My first post on this forum, so a brief intro: we're Brits living in
northern France (Normandy) for the last four years, though hoping to
return to the UK in the new few months.

I have a mower with a Briggs and Stratton XP40 mower which is not
running well. This will be only its third year of use, and I've never
had a problem with it until now. I used it for the first time this year
a few weeks ago - no problem, seemed to be running as normal. I then got
it out again last week and found that it wasn't running smoothly. I
would say the engine seems to be "hunting" - almost like it's coughing
slightly - it sounds at various points as though it's going to die but
always manages to keep going. Two further symptoms: (1) puffs of black
smoke are visible by the grill on the L/H side, and (2) it used an
awful lot more petrol than usual when I cut the grass with it the other
day.

I'm no mechanic, but have done my best to do the basics in an attempt
to rule out obvious causes: I've cleaned the air filter (seems fine),
taken off the plastic engine cover and cleaned round everything I can,
and changed the oil. Doesn't seem to have made any difference.

One other thing I've noticed: when first starting the engine (even
after only a few minutes' break in running), it seems to run nice and
smoothly for maybe ten seconds or so before starting to cough and
splutter again.

I would have taken it in for repair, but there's only one place in the
vicinity and they have a 3 week wait! I'd be very grateful if anyone
has any ideas or suggestions. (N.B. I've looked on the B&S site, but so
far only found quite generic advice that hasn't helped me.)


It's running rich. Almost certainly due to air inlet restriction at some
point. What kind of air filter does it have? If it's a bit of sponge, you
can make a replacement from a pan scrubber, one of those things that have a
yellow spongey bit one side and a green scrubby bit the other. My strimmer
is running well on one of these. Have you triwed running it without the air
filter? Bear in mind of course that then it will run weak and may nheed the
choke.

Steve


  #3  
Old 05-05-2009, 10:32 AM posted to uk.rec.gardening
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Posts: 737
Default Briggs & Stratton engine not running smoothly

On Tue, 5 May 2009 10:07:03 +0100, shazzbat wrote:

It's running rich. Almost certainly due to air inlet restriction at some
point.


Possibly but when my B&S exhibited the problem pretty much identical to
the OP's it's down to one of the little flap valves formed by the "gasket"
between the base of the carb and the fuel tank getting stuck into the hole
it is supposed to cover and block. So far I've managed to get it working
properly again by simply taking apart, flipping the flap out of the hole
and making sure the gasket is positioned with maximum overlay of this flap
and hole then putting back together.

Bear in mind of course that then it will run weak and may nheed the
choke.


If it has a choke...

--
Cheers
Dave.



  #4  
Old 05-05-2009, 11:19 AM posted to uk.rec.gardening
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Posts: 503
Default Briggs & Stratton engine not running smoothly

One other thing I've noticed: when first starting the engine (even
after only a few minutes' break in running), it seems to run nice and
smoothly for maybe ten seconds or so before starting to cough and
splutter again.


Sound like overfueling.
Without seeing the type of carb used on this engine I would imagine the
problem is with either the rubber diaphragm often located at the base of the
carb, or
Some carbs have an automatic choke butterfly which is supposed to flip back
once the engine is running this may be sticking. or
It has a manual choke you have forgotten to open.

Mike



  #5  
Old 05-05-2009, 03:34 PM
Registered User
 
First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi Steve,

Quote:
Originally Posted by shazzbat View Post
It's running rich. Almost certainly due to air inlet restriction at some point. What kind of air filter does it have? If it's a bit of sponge, you can make a replacement from a pan scrubber, one of those things that have a yellow spongey bit one side and a green scrubby bit the other. My strimmer is running well on one of these. Have you triwed running it without the air filter? Bear in mind of course that then it will run weak and may nheed the choke.
Thanks for your reply. That's what I thought too, but apparently not. The sponge air filter is pretty clean (and I've also now cleaned and oiled it as per the manufacturer's instructions). I did try running it without the air filter attached, and the problem persisted.

Rob
  #6  
Old 05-05-2009, 03:37 PM
Registered User
 
First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi Dave,

Quote:
Originally Posted by Dave Liquorice[_2_] View Post
Possibly but when my B&S exhibited the problem pretty much identical to
the OP's it's down to one of the little flap valves formed by the "gasket"
between the base of the carb and the fuel tank getting stuck into the hole
it is supposed to cover and block. So far I've managed to get it working
properly again by simply taking apart, flipping the flap out of the hole
and making sure the gasket is positioned with maximum overlay of this flap
and hole then putting back together.

Bear in mind of course that then it will run weak and may nheed the
choke.


If it has a choke...
Thanks for your reply. OK, sounds like I need to look further at the carb. Is it easy to get at the base of the carb where this gasket is located? Do I need to follow specialist instructions or should common sense and a careful approach be enough?

Thanks,

Rob
  #7  
Old 05-05-2009, 03:37 PM
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First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi again Dave,

I forgot to say, it doesn't have a choke.

Rob
  #8  
Old 05-05-2009, 03:39 PM
Registered User
 
First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi Mike,

Quote:
Originally Posted by Muddymike View Post
Sound like overfueling.
Without seeing the type of carb used on this engine I would imagine the
problem is with either the rubber diaphragm often located at the base of the
carb, or
Some carbs have an automatic choke butterfly which is supposed to flip back
once the engine is running this may be sticking. or
It has a manual choke you have forgotten to open.
Thanks for your reply. There is no choke, so we can rule that out. So it comes down to how easy or otherwise it will be for me to get the carb off and/or identify the automatic choke butterfly to which you referred. I won't say no to any tips...

Thanks,

Rob
  #9  
Old 05-05-2009, 10:58 PM posted to uk.rec.gardening
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Posts: 4,717
Default Briggs & Stratton engine not running smoothly


"robinfrance" wrote
My first post on this forum, so a brief intro: we're Brits living in
northern France (Normandy) for the last four years, though hoping to
return to the UK in the new few months.

I have a mower with a Briggs and Stratton XP40 mower which is not
running well. This will be only its third year of use, and I've never
had a problem with it until now. I used it for the first time this year
a few weeks ago no problem, seemed to be running as normal. I then got
it out again last week and found that it wasn't running smoothly. I
would say the engine seems to be "hunting" almost like it's coughing
slightly it sounds at various points as though it's going to die but
always manages to keep going. Two further symptoms: (1) puffs of black
smoke are visible by the grill on the L/H side, and (2) it used an
awful lot more petrol than usual when I cut the grass with it the other
day.

I'm no mechanic, but have done my best to do the basics in an attempt
to rule out obvious causes: I've cleaned the air filter (seems fine),
taken off the plastic engine cover and cleaned round everything I can,
and changed the oil. Doesn't seem to have made any difference.

One other thing I've noticed: when first starting the engine (even
after only a few minutes' break in running), it seems to run nice and
smoothly for maybe ten seconds or so before starting to cough and
splutter again.

I would have taken it in for repair, but there's only one place in the
vicinity and they have a 3 week wait! I'd be very grateful if anyone
has any ideas or suggestions. (N.B. I've looked on the B&S site, but so
far only found quite generic advice that hasn't helped me.)

Thanks in advance,

Hunting is when an engine speeds up and then slows down of it's own accord
instead of ticking over. This is usually caused by fuel starvation and
usually a dirty carburettor is the cause, sometimes a knackered fuel pump
but mowers don't have those.

However you mention it's using a lot more fuel than normal and making black
smoke which suggests it's actually running rich. Others have mentioned a
stuck choke but it could also be a stuck float in the carburettor. My
suggestion is to remove, partly dismantle, and clean the carb, just taking
the top of is usually enough to clean it out (use petrol not water). Make
sure the float moves easily and that there is no muck in the float chamber.

--
Regards
Bob Hobden
just W. of London





  #10  
Old 05-05-2009, 11:43 PM posted to uk.rec.gardening
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Posts: 737
Default Briggs & Stratton engine not running smoothly

On Tue, 5 May 2009 22:58:23 +0100, Bob Hobden wrote:

sometimes a knackered fuel pump but mowers don't have those.


Mine does. Manifold depression sucks a diaphram against a spring and that
movement (one way or the other) lifts fuel from the tank into a chamber
below the carburetor. There are a couple of flap valves as well, one of
those stuck open gave me the hunting problems.

Make sure the float moves easily and that there is no muck in the float
chamber.


No float but grud in the chambers or jets is a possibilty. No choke
either, cold start is aided by simply pressing the prime button 3 times
which squirts extra fuel into the inlet manifold. These single cyclinder,
small, air cooled 4 stroke engines don't need a choke like a 4 cylinder
water cooled car engine does. Once they have run for a few tens of seconds
they are warm enough not to require it.

--
Cheers
Dave.



  #11  
Old 06-05-2009, 07:58 AM
Registered User
 
First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi Bob,

Quote:
Originally Posted by Bob Hobden View Post
Hunting is when an engine speeds up and then slows down of it's own accord
instead of ticking over. This is usually caused by fuel starvation and
usually a dirty carburettor is the cause, sometimes a knackered fuel pump
but mowers don't have those.

However you mention it's using a lot more fuel than normal and making black
smoke which suggests it's actually running rich. Others have mentioned a
stuck choke but it could also be a stuck float in the carburettor. My
suggestion is to remove, partly dismantle, and clean the carb, just taking
the top of is usually enough to clean it out (use petrol not water). Make
sure the float moves easily and that there is no muck in the float chamber.
Thanks for the reply. Sounds like taking the top off the carb and giving it a good clean out is a sensible place to start. If that doesn't do the trick I guess I'll have to try taking the carb off to see what's underneath it.

It'll probably be the weekend before I get to it I'll post back with an update.

Thanks again to all,

Rob
  #12  
Old 06-05-2009, 02:12 PM posted to uk.rec.gardening
external usenet poster
 
Posts: 1
Default Briggs & Stratton engine not running smoothly

On Wed, 6 May 2009 07:58:05 +0100, robinfrance wrote:


Hi Bob,

Bob Hobden;842989 Wrote:

Hunting is when an engine speeds up and then slows down of it's own
accord
instead of ticking over. This is usually caused by fuel starvation and

usually a dirty carburettor is the cause, sometimes a knackered fuel
pump
but mowers don't have those.

However you mention it's using a lot more fuel than normal and making
black
smoke which suggests it's actually running rich. Others have mentioned
a
stuck choke but it could also be a stuck float in the carburettor. My
suggestion is to remove, partly dismantle, and clean the carb, just
taking
the top of is usually enough to clean it out (use petrol not water).
Make
sure the float moves easily and that there is no muck in the float
chamber.


Thanks for the reply. Sounds like taking the top off the carb and
giving it a good clean out is a sensible place to start. If that
doesn't do the trick I guess I'll have to try taking the carb off to
see what's underneath it.

It'll probably be the weekend before I get to it I'll post back with
an update.

Thanks again to all,

Rob


When you do that, pour the petrol in the tank into a glass jar and hold it up to the light.
When I had a similar problem, I found that the petrol contained very fine pieces of grass. I'm
guessing that the grass was fouling the filter on the carb.

Anyway, a good clean out and fresh petrol should solve your problem.

Rick... (The other Rick)

Science and sound engineering will always prevail in the end
"for nature cannot be fooled" [Feynman]
  #13  
Old 06-05-2009, 03:31 PM
Registered User
 
First recorded activity by GardenBanter: May 2009
Location: Normandy, France
Posts: 8
Default

Hi Risk,

Quote:
Originally Posted by Rick... (The other Rick)[_2_] View Post
When you do that, pour the petrol in the tank into a glass jar and hold it up to the light.
When I had a similar problem, I found that the petrol contained very fine pieces of grass. I'm
guessing that the grass was fouling the filter on the carb.

Anyway, a good clean out and fresh petrol should solve your problem.
Thanks, I'll bear that in mind. Though I was hoping not to have to empty the fuel tank, as that would mean changing the oil again, and I've already changed it once... (Manual says not to tip the mower without draining the oil.)

Rob
  #14  
Old 07-05-2009, 09:15 AM posted to uk.rec.gardening
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Posts: 737
Default Briggs & Stratton engine not running smoothly

On Wed, 6 May 2009 15:31:54 +0100, robinfrance wrote:

Thanks, I'll bear that in mind. Though I was hoping not to have to
empty the fuel tank, as that would mean changing the oil again, and
I've already changed it once... (Manual says not to tip the mower
without draining the oil.)


I think you'll find that the carb and fuel tank come away as a single unit
held onto the cylinder block with just a couple of bolts. Watch out for
the linkages/springs that connects to the vane under the fan cover that
regulates the engine speed according to load.

--
Cheers
Dave.



  #15  
Old 07-05-2009, 09:25 AM
Registered User
 
First recorded activity by GardenBanter: Apr 2009
Posts: 18
Default

Quote:
Originally Posted by robinfrance View Post
Hi everyone,

My first post on this forum, so a brief intro: we're Brits living in northern France (Normandy) for the last four years, though hoping to return to the UK in the new few months.

I have a mower with a Briggs and Stratton XP40 mower which is not running well. This will be only its third year of use, and I've never had a problem with it until now. I used it for the first time this year a few weeks ago no problem, seemed to be running as normal. I then got it out again last week and found that it wasn't running smoothly. I would say the engine seems to be "hunting" almost like it's coughing slightly it sounds at various points as though it's going to die but always manages to keep going. Two further symptoms: (1) puffs of black smoke are visible by the grill on the L/H side, and (2) it used an awful lot more petrol than usual when I cut the grass with it the other day.

I'm no mechanic, but have done my best to do the basics in an attempt to rule out obvious causes: I've cleaned the air filter (seems fine), taken off the plastic engine cover and cleaned round everything I can, and changed the oil. Doesn't seem to have made any difference.

One other thing I've noticed: when first starting the engine (even after only a few minutes' break in running), it seems to run nice and smoothly for maybe ten seconds or so before starting to cough and splutter again.

I would have taken it in for repair, but there's only one place in the vicinity and they have a 3 week wait! I'd be very grateful if anyone has any ideas or suggestions. (N.B. I've looked on the B&S site, but so far only found quite generic advice that hasn't helped me.)

Thanks in advance,

Rob
Hello Rob it seems as though theres to much petrol going through. Make sure the adjustment on the throttle cable isn't to high. Also how many times have you had it serviced in the 3 years ????
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