My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired
I'll take them apart and clean everything. Meanwhile, perhaps someone
with experience can suggest what I should be looking for. The sparkplug
is new, by the way. It does look rather sooty, but not at the business
end (close to the gap).

"Gib Bogle" wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden it
almost seems electrical, but in other respects it's as if the fuel in the
carburettor float chamber has been used up and not replenished - but of
course there is no float chamber, and the fuel system looks childishly
simple. The electrics are so simple - no moving parts except the
magneto - that it's hard to see what could go wrong there either. Maybe
there is something about the fuel system that I don't understand. I've
taken all the fuel-related bits off, and when I feel inspired I'll take
them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

duff capacitor on LT side?
does it restart? when cold? or hot?

Jim K

On Sun, 31 Jul 2011 17:22:00 +1200, Gib Bogle wrote:

The stop is so sudden it almost seems electrical, but in other respects
it's as if the fuel in the carburettor float chamber has been used up
and not replenished - but of course there is no float chamber, and the
fuel system looks childishly simple.

There is still a reservior with a pump to keep the level constant.
Have a dig about on the B&S site for the proper manaul for your
engine. The diaphragm might have failed or one of the flap valves
isn't working properly.

--
Cheers
Dave.

It'll stop dead as it's under load of sorts.
Electrically, as you say they are simple and if it was an electrical issue
you would have trouble starting every time.
Check the carb hasn't come adrift slightly and is sucking air, other than
that it's getting tired.
Local mower shop or Ebay source a carb repair kit strip and sort it. (Item
190556871460 might do the job but you will have to ask them about your model
or search for a kit for yours etc)
Also source a new air filter and a can of carb cleaner spray and don't prod
around with bits of wire in any ports or jets.
Change the plug and the oil at the same time. If the plug is fairly black
suspect piston rings, but that's usually after many years of use.

I used to look after a small fleet of these little buggers with several
el'cheapo makes of two smoke as well which revved like a bugger when the
field teams played with them during an 8 hour day.
All a much of a muchness really to look after.




My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired
I'll take them apart and clean everything. Meanwhile, perhaps someone
with experience can suggest what I should be looking for. The sparkplug
is new, by the way. It does look rather sooty, but not at the business
end (close to the gap).

On 31/07/2011 6:00 p.m., Jim K wrote:
"Gib wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden it
almost seems electrical, but in other respects it's as if the fuel in the
carburettor float chamber has been used up and not replenished - but of
course there is no float chamber, and the fuel system looks childishly
simple. The electrics are so simple - no moving parts except the
magneto - that it's hard to see what could go wrong there either. Maybe
there is something about the fuel system that I don't understand. I've
taken all the fuel-related bits off, and when I feel inspired I'll take
them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

duff capacitor on LT side?
does it restart? when cold? or hot?

It's very hard/impossible to start hot. I usually just give and put it
away for another day. My lawn is now quite long in the parts I haven't
got to.

I need to search for the capacitor.

On 31/07/2011 7:15 p.m., Dave Liquorice wrote:
On Sun, 31 Jul 2011 17:22:00 +1200, Gib Bogle wrote:

The stop is so sudden it almost seems electrical, but in other respects
it's as if the fuel in the carburettor float chamber has been used up
and not replenished - but of course there is no float chamber, and the
fuel system looks childishly simple.

There is still a reservior with a pump to keep the level constant.
Have a dig about on the B&S site for the proper manaul for your
engine. The diaphragm might have failed or one of the flap valves
isn't working properly.


Thanks for those leads. I haven't noticed anything resembling a pump,
will look more carefully later. This machine is more than 20 years old.
I bought it in the US and brought it back to NZ. SWMBO tells me to
buy a new one, but I feel it's almost good still.

On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

One simple thing to check, could the petrol reservoir cap air vent be
blocked? If it becomes blocked, you will gradually get a vacuum in the
tank. An easy way to check would be to wait until it stops and loosen
the cap. If you hear air rushing in and the engine then starts, invest
in a new cap or make a small hole in the old one.

--
Howard Neil

"Gib Bogle" wrote in message
...
On 31/07/2011 6:00 p.m., Jim K wrote:
"Gib wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it
almost seems electrical, but in other respects it's as if the fuel in
the
carburettor float chamber has been used up and not replenished - but of
course there is no float chamber, and the fuel system looks childishly
simple. The electrics are so simple - no moving parts except the
magneto - that it's hard to see what could go wrong there either. Maybe
there is something about the fuel system that I don't understand. I've
taken all the fuel-related bits off, and when I feel inspired I'll take
them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

duff capacitor on LT side?
does it restart? when cold? or hot?

It's very hard/impossible to start hot. I usually just give and put it
away for another day. My lawn is now quite long in the parts I haven't
got to.

I need to search for the capacitor.

my similarly ancient B&S (rotovator) engine was vertical shaft and capac is
under flywheel along with points etc....
"joy" i hear you say...;)
try fuel ideas first? amazing what spares are still about for old
carbs/engines on ebay.

(altho if it's a carb diaphragm prob how does it even start? is there a
primer bulb or similar? mine hasn't, it's a crankshaft powered "kind of a"
pump with (IIRC) 2 diaphragms in the carb...

Jim K

Gib Bogle wrote:
On 31/07/2011 6:00 p.m., Jim K wrote:
"Gib wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so
sudden it
almost seems electrical, but in other respects it's as if the fuel in
the
carburettor float chamber has been used up and not replenished - but of
course there is no float chamber, and the fuel system looks childishly
simple. The electrics are so simple - no moving parts except the
magneto - that it's hard to see what could go wrong there either. Maybe
there is something about the fuel system that I don't understand. I've
taken all the fuel-related bits off, and when I feel inspired I'll take
them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

duff capacitor on LT side?
does it restart? when cold? or hot?

It's very hard/impossible to start hot. I usually just give and put it
away for another day. My lawn is now quite long in the parts I haven't
got to.

I need to search for the capacitor.

they have had some sort of magneto solid state thingie for years havent
they?

"Gib Bogle" wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden it
almost seems electrical,
Does it have a "stop" wire somewhere on the throttle linkage? I have known
these short out and cause the sort of problem you describe. The work by
shorting the ignition to earth when the throttle is closed.

Mike

On Sun, 31 Jul 2011 17:22:00 +1200, Gib Bogle wrote:

My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.

What engine is it? Does it have an obvious HP rating or a model number
(model numbers sometimes stamped into the front of the cowling which sits
around the flywheel)

I'm used to 4-stroke B+S 10 and 11 HP engines as I've got a couple of
those, but I don't think I've ever had cause to mess with their smaller
stuff.

cheers

Jules

"Gib Bogle" wrote in message
...
On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

thinking on a bit, when it conks whip the plug out and check for a spark
when someone pulls the starter rope- that will narrow it down to one or the
other (fuel vs elecs)

Jim K

On 1/08/2011 3:21 a.m., Jim K wrote:
"Gib wrote in message
...
On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

thinking on a bit, when it conks whip the plug out and check for a spark
when someone pulls the starter rope- that will narrow it down to one or the
other (fuel vs elecs)

I've tested the spark (by myself, which isn't very satisfactory), but
not just after it conks out. The spark is weak.

There no engine number, so I can't use the B&S site to search for a
manual. The only identification on the engine is Classic 3.5 HP.

"Gib Bogle" wrote in message
...
On 1/08/2011 3:21 a.m., Jim K wrote:
"Gib wrote in message
...
On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

thinking on a bit, when it conks whip the plug out and check for a spark
when someone pulls the starter rope- that will narrow it down to one or
the
other (fuel vs elecs)

I've tested the spark (by myself, which isn't very satisfactory), but not
just after it conks out. The spark is weak.

There no engine number, so I can't use the B&S site to search for a
manual. The only identification on the engine is Classic 3.5 HP.

does this help narrow it down?

http://www.briggsbits.co.uk/acatalog...hp.html#sprint

Jiim K

On 31/07/2011 21:45, Gib Bogle wrote:
On 1/08/2011 3:21 a.m., Jim K wrote:
"Gib wrote in message
...
On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

thinking on a bit, when it conks whip the plug out and check for a spark
when someone pulls the starter rope- that will narrow it down to one
or the
other (fuel vs elecs)

I've tested the spark (by myself, which isn't very satisfactory), but
not just after it conks out. The spark is weak.

There no engine number, so I can't use the B&S site to search for a
manual. The only identification on the engine is Classic 3.5 HP.

I've had a simililar problem on the B&S small 4 stroke, cutting out
under load. Turned out to be the inlet manifold cracked, cost about £7
IIRC to replace.

Chrs K

On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

Well, you've been given a fair number of things to check:
* duff diaphragm in carb
* airlock in fuel system
* ignition cutout operating when it shouldn't, etc.

One other thing to check is the (ultra crude!) auto speed control
mechanism. The throttle cable doesn't open the throttle directly, but
does so via a spring. There's another spring, connected to a vane, which
is trying to shut it. The vane is blown by some fins which rotate with
the flywheel - the faster the rotation, the greater the force. the
actual speed is determined by the equilibrium point between these two
forces - and the idea is the speed remains more or less constant
regardless of load. If bits of grass and other debris get inside the
housing where the vane is, they can interfere with its operation. I'm
not sure whether this would cause your symptoms, but it's easy enough to
eliminate. You just need to remove the top cover of the engine, complete
with recoil starter mechanism, and clean out the housing.

With regard to spares, I get the impression that B&S have used the same
diaphragm in most of their carbs since Adam was a lad, so getting a
replacement shouldn't be a problem.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 31/07/2011 8:38 p.m., Chris Hogg wrote:
On Sun, 31 Jul 2011 17:22:00 +1200, Gib
wrote:

My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired
I'll take them apart and clean everything. Meanwhile, perhaps someone
with experience can suggest what I should be looking for. The sparkplug
is new, by the way. It does look rather sooty, but not at the business
end (close to the gap).

I have recently had a similar problem with my 10+ yr old B&S mower,
discussed over on uk.rec.gardening in the last few days. It would run
for a minute or so and then stop. Pumping the fuel primer bulb got it
going again for another minute or so. Popular suggestions were the
rubber diaphragm in the fuel pump/carb had perished, or the vent holes
in the fuel filler cap had become blocked. The latter can be checked
by running with the filler cap loose or off altogether. The following
may give you some ideas:

http://www.briggsandstratton.com/eng...he-carburetor/

Current thinking is that my problem was simply a blocked filler cap
vent.

Thanks, Howard Neil has the same idea. No fuel primer bulb on this
engine. It is about 20 years old, and the carb is very simple.

On 1/08/2011 9:03 a.m., Jim K wrote:
"Gib wrote in message
...
On 1/08/2011 3:21 a.m., Jim K wrote:
"Gib wrote in message
...
On 31/07/2011 7:46 p.m., Londonman wrote:
It'll stop dead as it's under load of sorts.

These stops can occur under no load.

Electrically, as you say they are simple and if it was an electrical
issue you would have trouble starting every time.

Unless it's intermittent.

Check the carb hasn't come adrift slightly and is sucking air, other
than that it's getting tired.

Everything was screwed down tight. I'm certainly getting tired.

Local mower shop or Ebay source a carb repair kit strip and sort it.
(Item 190556871460 might do the job but you will have to ask them about
your model or search for a kit for yours etc)

Thanks, it's possible that the kit will be available locally, but not
likely, given the age of the mower.

Also source a new air filter and a can of carb cleaner spray and don't
prod around with bits of wire in any ports or jets.

I'm used to working on bike carbs, probably will not do anything stupid.

Change the plug and the oil at the same time. If the plug is fairly
black suspect piston rings, but that's usually after many years of use.

thinking on a bit, when it conks whip the plug out and check for a spark
when someone pulls the starter rope- that will narrow it down to one or
the
other (fuel vs elecs)

I've tested the spark (by myself, which isn't very satisfactory), but not
just after it conks out. The spark is weak.

There no engine number, so I can't use the B&S site to search for a
manual. The only identification on the engine is Classic 3.5 HP.

does this help narrow it down?

http://www.briggsbits.co.uk/acatalog...hp.html#sprint

Jiim K



It doesn't look exactly like that engine. It might have been sold only
in the US (where I bought it). I'm guessing that this is the simplest
(cheapest, nastiest) engine that B&S ever made. The carb, which is
plastic, is simpler than the old 3.5 hp version I've seen online. It
has only one intake tube+gauze filter, instead of the usual two.

I cleaned the carb and petrol tank (neither looked dirty, no sign of
water), checked that the filter was clean (I cleaned it recently),
changed the oil (way overdue), reassembled and ran it. I was able to
make good headway on the lawn until it bogged down on a thick patch -
this is normal. So far it looks OK. If the problem recurs the next
step is to pull the flywheel off and look at the points (and if
necessary the capacitor), since the spark is always weak.

Thanks to all for helpful suggestions.

On 31/07/2011 8:39 p.m., Howard Neil wrote:
On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).

One simple thing to check, could the petrol reservoir cap air vent be
blocked? If it becomes blocked, you will gradually get a vacuum in the
tank. An easy way to check would be to wait until it stops and loosen
the cap. If you hear air rushing in and the engine then starts, invest
in a new cap or make a small hole in the old one.


The cap vent is not blocked.

On 1/08/2011 12:05 a.m., MuddyMike wrote:
"Gib wrote in message
...
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden it
almost seems electrical,
Does it have a "stop" wire somewhere on the throttle linkage? I have known
these short out and cause the sort of problem you describe. The work by
shorting the ignition to earth when the throttle is closed.

Mike

I thought of that, but it looks OK.

On 1/08/2011 3:09 a.m., Jules Richardson wrote:
On Sun, 31 Jul 2011 17:22:00 +1200, Gib Bogle wrote:

My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.

What engine is it? Does it have an obvious HP rating or a model number
(model numbers sometimes stamped into the front of the cowling which sits
around the flywheel)

No engine number anywhere.

On 1/08/2011 9:38 a.m., Roger Mills wrote:

One other thing to check is the (ultra crude!) auto speed control
mechanism. The throttle cable doesn't open the throttle directly, but
does so via a spring. There's another spring, connected to a vane, which
is trying to shut it. The vane is blown by some fins which rotate with
the flywheel - the faster the rotation, the greater the force. the
actual speed is determined by the equilibrium point between these two
forces - and the idea is the speed remains more or less constant
regardless of load. If bits of grass and other debris get inside the
housing where the vane is, they can interfere with its operation. I'm
not sure whether this would cause your symptoms, but it's easy enough to
eliminate. You just need to remove the top cover of the engine, complete
with recoil starter mechanism, and clean out the housing.

I've checked that, all OK.

With regard to spares, I get the impression that B&S have used the same
diaphragm in most of their carbs since Adam was a lad, so getting a
replacement shouldn't be a problem.

Actually the diaphragm is different from that on at least some other
carbs - the YouTube videos I looked at (for an old 3.5 hp engine) have a
carb with two intake tubes, while mine has just one.

On 02/08/2011 11:04, wrote:
Thus spake Gib Bogle ) unto the assembled multitudes:

Thanks for those leads. I haven't noticed anything resembling a pump,
will look more carefully later. This machine is more than 20 years old.

I bought it in the US and brought it back to NZ.

Gosh, and there's me complaining about driving 10 miles to buy a lawn mower ;-)



Indeed. I wonder how long it took - at 3MPH - to get from USA to NZ! g
--
Cheers,
Roger
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"Roger Mills" wrote in message
...
On 02/08/2011 11:04, wrote:
Thus spake Gib Bogle ) unto the assembled
multitudes:

Thanks for those leads. I haven't noticed anything resembling a pump,
will look more carefully later. This machine is more than 20 years old.

I bought it in the US and brought it back to NZ.

Gosh, and there's me complaining about driving 10 miles to buy a lawn
mower ;-)



Indeed. I wonder how long it took - at 3MPH - to get from USA to NZ! g
--

about as long as it takes google groups to get back up again this time?

Jim K

On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).
Probably not the same as you have a magneto and, I assume, no battery,
but I had a similar problem with my B&S powered lawn tractor. I traced
the problem to the solenoid at the bottom of the carb. The purpose is to
retract a needle from the main jet to permit the petrol to enter and to
shut it off once the ignition is turned off to prevent 'afterfire'.

I replaced the solenoid with the appropriate UNF(?) bolt cut down to
length and, provided I slow the engine to idle before stopping, I have
no more problems with it.

In message , Pete
Shew writes
On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).
Probably not the same as you have a magneto and, I assume, no battery,
but I had a similar problem with my B&S powered lawn tractor. I traced
the problem to the solenoid at the bottom of the carb. The purpose is
to retract a needle from the main jet to permit the petrol to enter and
to shut it off once the ignition is turned off to prevent 'afterfire'.

I replaced the solenoid with the appropriate UNF(?) bolt cut down to
length and, provided I slow the engine to idle before stopping, I have
no more problems with it.

Do you also have a manual shut off valve?

My Jonsered (different engine) has the same feature and, once or twice a
season, would fill the cylinders with neat petrol.

regards



--
Tim Lamb

On Sun, 31 Jul 2011 17:22:00 +1200, Gib Bogle wrote:

I've taken all the fuel-related bits off, and when I feel inspired
I'll take them apart and clean everything. Meanwhile, perhaps someone
with experience can suggest what I should be looking for. The sparkplug
is new, by the way. It does look rather sooty, but not at the business
end (close to the gap).

This: http://www.repairfaq.org/sam/lmfaq.htm#lmedwrwh suggests it might be a
bad condenser/points.

More likely because you've checked the fuel side...

Thomas Prufer

On 03/08/2011 19:23, Tim Lamb wrote:
In message , Pete
Shew writes
On 31/07/2011 06:22, Gib Bogle wrote:
My trusty old mower is no longer trusty. It starts OK, and runs for a
couple of circuits of the lawn, then stops dead. The stop is so sudden
it almost seems electrical, but in other respects it's as if the fuel in
the carburettor float chamber has been used up and not replenished - but
of course there is no float chamber, and the fuel system looks
childishly simple. The electrics are so simple - no moving parts except
the magneto - that it's hard to see what could go wrong there either.
Maybe there is something about the fuel system that I don't understand.
I've taken all the fuel-related bits off, and when I feel inspired I'll
take them apart and clean everything. Meanwhile, perhaps someone with
experience can suggest what I should be looking for. The sparkplug is
new, by the way. It does look rather sooty, but not at the business end
(close to the gap).
Probably not the same as you have a magneto and, I assume, no battery,
but I had a similar problem with my B&S powered lawn tractor. I traced
the problem to the solenoid at the bottom of the carb. The purpose is
to retract a needle from the main jet to permit the petrol to enter
and to shut it off once the ignition is turned off to prevent
'afterfire'.

I replaced the solenoid with the appropriate UNF(?) bolt cut down to
length and, provided I slow the engine to idle before stopping, I have
no more problems with it.

Do you also have a manual shut off valve?

My Jonsered (different engine) has the same feature and, once or twice a
season, would fill the cylinders with neat petrol.

regards



No, no manual fuel tap, just the solenoid which stops the fuel leaving
the float chamber via the main jet. It was probably developed as a nasty
fix for when users turn off the engine at full throttle and are startled
by the bangs from the exhaust.

For some reason mine got weak when warm and couldn't pull the needle
down against the spring so shutting off the fuel. The solenoid seems
difficult to disassemble without damage and as a new one is close to
£100! it seems that a 10p set screw was the correct fix.

Pete

To wrap this up: my trusty, incredibly simple, old B&S is now trusty
again. I thoroughly cleaned the carb and tank, changed the oil, and
then did the lawn with no sudden conking out. There was no obvious
problem anywhere - no water in the oil or petrol, little sediment in the
tank - but whatever it was it seems to be fixed. I didn't need to check
the points, but should take a look some time. Thanks for all the advice
and interesting comments.

Gib Bogle wrote:
To wrap this up: my trusty, incredibly simple, old B&S is now trusty
again. I thoroughly cleaned the carb and tank, changed the oil, and
then did the lawn with no sudden conking out. There was no obvious
problem anywhere - no water in the oil or petrol, little sediment in the
tank - but whatever it was it seems to be fixed. I didn't need to check
the points, but should take a look some time. Thanks for all the advice
and interesting comments.


Classic bit of grit in the carb behaviour ....


fit fuel filter?

On 5/08/2011 8:55 a.m., The Natural Philosopher wrote:
Gib Bogle wrote:
To wrap this up: my trusty, incredibly simple, old B&S is now trusty
again. I thoroughly cleaned the carb and tank, changed the oil, and
then did the lawn with no sudden conking out. There was no obvious
problem anywhere - no water in the oil or petrol, little sediment in
the tank - but whatever it was it seems to be fixed. I didn't need to
check the points, but should take a look some time. Thanks for all the
advice and interesting comments.


Classic bit of grit in the carb behaviour ....


fit fuel filter?

Where? The carb is bolted on the top of the petrol tank. A tube sticks
down into the petrol. It has a gauze filter on the end.

Gib Bogle wrote:
On 5/08/2011 8:55 a.m., The Natural Philosopher wrote:
Gib Bogle wrote:
To wrap this up: my trusty, incredibly simple, old B&S is now trusty
again. I thoroughly cleaned the carb and tank, changed the oil, and
then did the lawn with no sudden conking out. There was no obvious
problem anywhere - no water in the oil or petrol, little sediment in
the tank - but whatever it was it seems to be fixed. I didn't need to
check the points, but should take a look some time. Thanks for all the
advice and interesting comments.


Classic bit of grit in the carb behaviour ....


fit fuel filter?

Where? The carb is bolted on the top of the petrol tank. A tube sticks
down into the petrol. It has a gauze filter on the end.

Ah. That should have been enough.