I posted here in November regarding a petrol lawnmower that was refusing to
start. It's a Tecumseh BVS143 4-stroke engine on an unnamed box, so nothing
special.

Anyway, before it was running for about 1-3 seconds before cutting out. I
eventually traced it down to a perished spark lead, and today I replaced the
electronic coil/lead unit with a good condition used part. Earlier this
year I also changed the oil (it was filthy) for new 15w/40 and cleaned the
spark plug and air filter. Today I put in new petrol (bought today) and
oiled the air filter.

The five lines of print that came with the new coil said to adjust the
magneto gap between magnet and laminations to 0.30mm. But I don't have
their gauging tool, so I googled the thickness of a piece of 80gsm paper to
be 0.10mm, and used three sheets. It started, and continued to run, but it
didn't have much power to tackle thick grass and was misfiring every 4-5
cycles. I did leave it to run for a while to clear out any clag, but it
seemed to be running clean after the first minute or two.

So I tried several paper thicknesses:
1-2 sheets - cuts out after 1-3s
3-4 - runs, some degree of misfire
5 - misfiring 60%+ of the time, but enough to run without load just about

So is there an easy way to adjust the coil gap? I'm guessing it must be
possible to get hold of a little kit of plasticard spacers of relevant
thicknesses or something similar - any suggestions from where?

Also, anything else I should be looking at for solving the misfiring? I
didn't wring out the air filter, so maybe it has too much oil? What else?
I haven't looked at the fuel filter or the carburettor (can't work out how
to find these) - would these be the cause, or is it likely to be just the
coil gap?

Thanks
Theo

Theo Markettos wrote:

I posted here in November regarding a petrol lawnmower that was refusing to
start. It's a Tecumseh BVS143 4-stroke engine on an unnamed box, so nothing
special.
snip
So is there an easy way to adjust the coil gap? I'm guessing it must be
possible to get hold of a little kit of plasticard spacers of relevant
thicknesses or something similar - any suggestions from where?

Has it got a good spark? If so, then the gap is fine.

Also, anything else I should be looking at for solving the misfiring?

Shit in the carb.
Take the carb apart and spray it thoroughly with carb cleaner spray.
Make sure it goes into all of the little holes and jets, and that they
are clear.
It should work fine then. - my dealer says 90% of mower faults are
blocked carburettors.
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

On 04 Aug 2007 20:01:45 +0100 (BST), Theo Markettos wrote:

I posted here in November regarding a petrol lawnmower that was refusing
to
start. It's a Tecumseh BVS143 4-stroke engine on an unnamed box, so
nothing
special.

Anyway, before it was running for about 1-3 seconds before cutting out.
I
eventually traced it down to a perished spark lead, and today I replaced
the
electronic coil/lead unit with a good condition used part. Earlier this
year I also changed the oil (it was filthy) for new 15w/40 and cleaned
the
spark plug and air filter. Today I put in new petrol (bought today) and
oiled the air filter.

The five lines of print that came with the new coil said to adjust the
magneto gap between magnet and laminations to 0.30mm. But I don't have
their gauging tool, so I googled the thickness of a piece of 80gsm paper
to
be 0.10mm, and used three sheets. It started, and continued to run, but
it
didn't have much power to tackle thick grass and was misfiring every 4-5
cycles. I did leave it to run for a while to clear out any clag, but it
seemed to be running clean after the first minute or two.

So I tried several paper thicknesses:
1-2 sheets - cuts out after 1-3s
3-4 - runs, some degree of misfire
5 - misfiring 60%+ of the time, but enough to run without load just
about

So is there an easy way to adjust the coil gap? I'm guessing it must be
possible to get hold of a little kit of plasticard spacers of relevant
thicknesses or something similar - any suggestions from where?

Also, anything else I should be looking at for solving the misfiring? I
didn't wring out the air filter, so maybe it has too much oil? What
else?
I haven't looked at the fuel filter or the carburettor (can't work out
how
to find these) - would these be the cause, or is it likely to be just
the
coil gap?

Thanks
Theo

--
Cheers
Dave. pam is missing e-mail

On 04 Aug 2007 20:01:45 +0100 (BST), Theo Markettos wrote:

So is there an easy way to adjust the coil gap? I'm guessing it must be
possible to get hold of a little kit of plasticard spacers of relevant
thicknesses or something similar - any suggestions from where?

Halfords will alomst certainly have a feeler gauge set. If my maths is
right 0.3mm is a little less than 8 thou.

--
Cheers
Dave. pam is missing e-mail

Theo,
the symptoms suggest a partially blocked carburettor main jet. Enough fuel
getting through for idling but not enough for full power.
David

"Theo Markettos" wrote in message
...
I posted here in November regarding a petrol lawnmower that was refusing
to
start. It's a Tecumseh BVS143 4-stroke engine on an unnamed box, so
nothing
special.

Anyway, before it was running for about 1-3 seconds before cutting out. I
eventually traced it down to a perished spark lead, and today I replaced
the
electronic coil/lead unit with a good condition used part. Earlier this
year I also changed the oil (it was filthy) for new 15w/40 and cleaned the
spark plug and air filter. Today I put in new petrol (bought today) and
oiled the air filter.

The five lines of print that came with the new coil said to adjust the
magneto gap between magnet and laminations to 0.30mm. But I don't have
their gauging tool, so I googled the thickness of a piece of 80gsm paper
to
be 0.10mm, and used three sheets. It started, and continued to run, but
it
didn't have much power to tackle thick grass and was misfiring every 4-5
cycles. I did leave it to run for a while to clear out any clag, but it
seemed to be running clean after the first minute or two.

So I tried several paper thicknesses:
1-2 sheets - cuts out after 1-3s
3-4 - runs, some degree of misfire
5 - misfiring 60%+ of the time, but enough to run without load just about

So is there an easy way to adjust the coil gap? I'm guessing it must be
possible to get hold of a little kit of plasticard spacers of relevant
thicknesses or something similar - any suggestions from where?

Also, anything else I should be looking at for solving the misfiring? I
didn't wring out the air filter, so maybe it has too much oil? What else?
I haven't looked at the fuel filter or the carburettor (can't work out how
to find these) - would these be the cause, or is it likely to be just the
coil gap?

Thanks
Theo

On 4 Aug, 20:01, Theo Markettos
wrote:
1-2 sheets - cuts out after 1-3s
3-4 - runs, some degree of misfire
5 - misfiring 60%+ of the time, but enough to run without load just about

Not familiar with this particular engine, but in general the magneto
gap affects the spark amplitude, but not timing. Again, in general,
the amplitude is not very important. As the other posters say the
carb is a good place to go, or indeed a new plug. To alter timing you
would need to move the coil radially around the flywheel.

In the old days it was common to put a "keeper" on the magnet when
removing the flywheel, but I think it is an urban myth - the magnetic
circuit is only closed when the magnet passes the coil.

Davy wrote:
Theo,
the symptoms suggest a partially blocked carburettor main jet. Enough fuel
getting through for idling but not enough for full power.

Thanks. Whereabouts would I find the carburettor - just follow the fuel
line? Is that where the throttle cable goes (which incidentally at the
moment only really has two positions, start/on and a tiny bit further down
splutter/die). Or should I take the flywheel assembly apart? I don't have
any documentation, so I don't know where things are likely to be.

The spark plug and air filter were pretty filthy, so I wouldn't be surprised
if there were things blocked inside.

Theo

"Theo Markettos" wrote in message
...
Davy wrote:
Theo,
the symptoms suggest a partially blocked carburettor main jet. Enough
fuel
getting through for idling but not enough for full power.

Thanks. Whereabouts would I find the carburettor - just follow the fuel
line? Is that where the throttle cable goes (which incidentally at the
moment only really has two positions, start/on and a tiny bit further down
splutter/die). Or should I take the flywheel assembly apart? I don't have
any documentation, so I don't know where things are likely to be.

The spark plug and air filter were pretty filthy, so I wouldn't be
surprised
if there were things blocked inside.

Theo

Air filter VERY important. Clean that before you do anything else. The
machine demands air to run, blocked filter starves it of air. FULL STOP
ENGINE.

Spark plug almost as important. A wire brush will clean that and as a VERY
VERY rough guide, the gap between the electrodes should be the thickness of
a thumb nail.

Mike


--
The Royal Naval Electrical Branch Association.
'THE' Association if you served in the Electrical Branch of the Royal Navy
Reunion Bournemouth August/September 2007
www.rneba.org.uk
"Navy Days" Portsmouth 25th - 27th July 2008. RN Shipmates will have a Stand

Did anyone reading this have a Lambretta LI150 with twin seats in the early
60's when flared skirts were the rage?

Air starvation? Tell me about it :-((((

Mike



--
The Royal Naval Electrical Branch Association.
'THE' Association if you served in the Electrical Branch of the Royal Navy
Reunion Bournemouth August/September 2007
www.rneba.org.uk
"Navy Days" Portsmouth 25th - 27th July 2008. RN Shipmates will have a Stand




"Theo Markettos" wrote in message
...
Davy wrote:
Theo,
the symptoms suggest a partially blocked carburettor main jet. Enough
fuel
getting through for idling but not enough for full power.

Thanks. Whereabouts would I find the carburettor - just follow the fuel
line? Is that where the throttle cable goes (which incidentally at the
moment only really has two positions, start/on and a tiny bit further down
splutter/die). Or should I take the flywheel assembly apart? I don't have
any documentation, so I don't know where things are likely to be.

The spark plug and air filter were pretty filthy, so I wouldn't be
surprised
if there were things blocked inside.

Theo

"'Mike'" wrote in message
...
Air filter VERY important. Clean that before you do anything else. The
machine demands air to run, blocked filter starves it of air. FULL STOP
ENGINE.

That one caught me out. I had tipped the mower over to sharpen the blade.
When I tried to start it again it wouldn't run and was very smokey. Turned
out the air filter paper was flooded with petrol and dust.

Dave Liquorice wrote:
Halfords will alomst certainly have a feeler gauge set. If my maths is
right 0.3mm is a little less than 8 thou.

Thanks, knowing the name for it was the problem! I've just ebayed myself a
set.

Theo

'Mike' wrote:
Air filter VERY important. Clean that before you do anything else. The
machine demands air to run, blocked filter starves it of air. FULL STOP
ENGINE.

Spark plug almost as important. A wire brush will clean that and as a VERY
VERY rough guide, the gap between the electrodes should be the thickness of
a thumb nail.

I realised those - they were dirty but cleaning them was the first thing I
did when I started working on the mower I did toothbrush and meths
treatment on the plug - scraped away much of the carbon on it.

Though the clean and dry air filter sponge soaked up much more oil than I
expected... should I squeeze out as much oil as possible (to allow the
airflow) or is it better to keep some in (to collect bits of dust, I
assume)? I don't think it was originally very oily, but the previous owners
of the mower did zero maintenance on it so that's probably not a guide.
FWIW in testing (on concrete, not cutting anything, not dusty air) I ran it
with no air filter until I got it started.

Theo

Spark plug almost as important. A wire brush will clean that and as a
VERY
VERY rough guide, the gap between the electrodes should be the thickness
of
a thumb nail.

I realised those - they were dirty but cleaning them was the first thing I
did when I started working on the mower I did toothbrush and meths
treatment on the plug - scraped away much of the carbon on it.


Great :-))

Though the clean and dry air filter sponge soaked up much more oil than I
expected... should I squeeze out as much oil as possible (to allow the
airflow) or is it better to keep some in (to collect bits of dust, I
assume)?

If it is the sponge type without the cardboard stifeners/case etc, then I
would wash it out in hot soapy water. It needs to be clean to allow the air
to go through, leave a film of oil in it and it will clog again.


I don't think it was originally very oily, but the previous owners
of the mower did zero maintenance on it so that's probably not a guide.
FWIW in testing (on concrete, not cutting anything, not dusty air) I ran
it
with no air filter until I got it started.

You can run the engine without the air filter and that should prove one way
or the other. If it runs OK without the filter but not with it, there is
your problem ........ 'sort of' because you are now down to tuning.

BUT, to run it on concrete without the filter is not a good idea. The filter
is there to stop impurities entering the engine and scoring the bores of the
cylinder. Concrete is very abrasive and any dust thrown up and into the
engine will not do it any good. If you have a large sheet of ply or
harboard, run it on that

Mike


--
The Royal Naval Electrical Branch Association.
'THE' Association if you served in the Electrical Branch of the Royal Navy
Reunion Bournemouth August/September 2007
www.rneba.org.uk
"Navy Days" Portsmouth 25th - 27th July 2008. RN Shipmates will have a Stand

On Sun, 5 Aug 2007 20:53:03 +0100, Mike wrote:

If it is the sponge type without the cardboard stifeners/case etc, then
I would wash it out in hot soapy water. It needs to be clean to allow
the air to go through, leave a film of oil in it and it will clog again.

They vary. A plain foam filter without oil won't trap the fine muck that
blocks up carbs. It doesn't want to to be dripping in oil though just have
a film of oil to trap the tiny bits of dust.

You can run the engine without the air filter and that should prove one
way or the other. If it runs OK without the filter but not with it,
there is your problem ........ 'sort of' because you are now down to
tuning.

And the filter being there or not even a proper one will affect the vacuum
and thus the mixture, though if it runs a lot better at highre revs
without the filter it is a pretty good indication that not enough air is
being allowed in.

Has the OP done a google on Teuschmesh(sp) engines? I wouldn't be
surprised to find the manual online somewhere.

--
Cheers
Dave. pam is missing e-mail

'Mike' wrote:
Did anyone reading this have a Lambretta LI150 with twin seats in the early
60's when flared skirts were the rage?

Air starvation? Tell me about it :-((((

I'm afraid I wasn't even born then
Hence the teach-yourself-engines I'm doing at the moment...

Theo