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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 |
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 |
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. |
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 |
Hi Steve,
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Rob |
Hi Dave,
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Thanks, Rob |
Hi again Dave,
I forgot to say, it doesn't have a choke. Rob |
Hi Mike,
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Thanks, Rob |
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 |
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. |
Hi Bob,
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It'll probably be the weekend before I get to it – I'll post back with an update. Thanks again to all, Rob |
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] |
Hi Risk,
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Rob |
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. |
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