Posted by GodfreyY on September 10, 2011, 9:52 am
I recently had the common problem of engine running rough, puffs of
black smoke etc. It had been used for four seasons with no maintenance
whatsoever so I changed the oil, fitted new air filter, spark plug and
fuel diaphram. The engine ran perfectly for two mowings but the next
time it absolutely refused to start at all. I inspected the plug which
was very wet so took another look at the diaphram and fuel filters which
seemed OK. Checked for a spark at the plug, which also seems OK so I
tried to check compression. Following a suggestion I found elsewhere on
the web, with the plug lead off, the engine brake lever tied to off
position, I turned the engine backwards. I could feel resistance at one
point but after turning it past that, it took two whole turns before it
resisted again.
I would be really grateful if anyone is able to tell me if this is
normal, or indeed make any other suggestions as to what the problem
might be.
Many thanks.
--
GodfreyY
Posted by Bob Hobden on September 10, 2011, 11:33 am
"GodfreyY" wrote ...
>I recently had the common problem of engine running rough, puffs of
>black smoke etc. It had been used for four seasons with no maintenance
>whatsoever so I changed the oil, fitted new air filter, spark plug and
>fuel diaphram. The engine ran perfectly for two mowings but the next
>time it absolutely refused to start at all. I inspected the plug which
>was very wet so took another look at the diaphram and fuel filters which
>seemed OK. Checked for a spark at the plug, which also seems OK so I
>tried to check compression. Following a suggestion I found elsewhere on
>the web, with the plug lead off, the engine brake lever tied to off
>position, I turned the engine backwards. I could feel resistance at one
>point but after turning it past that, it took two whole turns before it
>resisted again.
>I would be really grateful if anyone is able to tell me if this is
>normal, or indeed make any other suggestions as to what the problem
>might be.
>Many thanks.
It's a 4 stroke engine so two complete revolutions of the flywheel between
each compression stroke. It goes...bang and power, piston moves down;
exhaust, piston moves up pushing out the old gas; Inlet, piston moves down
sucking in new gas; compression, piston moves up to compress the gas....
A wet plug shows either too much petrol compared to air or no spark. Spark
should be blue not yellow, check the air filters again to ensure air can
flow, I've known an engine try to ingest it's foam filter if not fitted
properly.
--
Regards. Bob Hobden.
Posted to this Newsgroup from the W of London, UK
Posted by Anarchy on September 10, 2011, 2:03 pm
> "GodfreyY" wrote ...
> >I recently had the common problem of engine running rough, puffs of
> >black smoke etc. It had been used for four seasons with no maintenance
> >whatsoever so I changed the oil, fitted new air filter, spark plug and
> >fuel diaphram. The engine ran perfectly for two mowings but the next
> >time it absolutely refused to start at all. I inspected the plug which
> >was very wet so took another look at the diaphram and fuel filters which
> >seemed OK. Checked for a spark at the plug, which also seems OK so I
> >tried to check compression. Following a suggestion I found elsewhere on
> >the web, with the plug lead off, the engine brake lever tied to off
> >position, I turned the engine backwards. I could feel resistance at one
> >point but after turning it past that, it took two whole turns before it
> >resisted again.
> >I would be really grateful if anyone is able to tell me if this is
> >normal, or indeed make any other suggestions as to what the problem
> >might be.
> >Many thanks.
> It's a 4 stroke engine so two complete revolutions of the flywheel between
> each compression stroke. It goes...bang and power, piston moves down;
> exhaust, piston moves up pushing out the old gas; Inlet, piston moves down
> sucking in new gas; compression, piston moves up to compress the gas....
> A wet plug shows either too much petrol compared to air or no spark. Spark
> should be blue not yellow, check the air filters again to ensure air can
> flow, I've known an engine try to ingest it's foam filter if not fitted
> properly.
> --
> Regards. Bob Hobden.
> Posted to this Newsgroup from the W of London, UK
First thing to do is fit a new spark plug (new, not an old one
cleaned), and then turn the motor over on the starter with plug
removed (but fitted into cap and earthed onto engine), to remove the
unburnt fuel. Try it again and with any luck it will then run fine.
Posted by NT on September 10, 2011, 9:32 pm
wrote:
> I recently had the common problem of engine running rough, puffs of
> black smoke etc. It had been used for four seasons with no maintenance
> whatsoever so I changed the oil, fitted new air filter, spark plug and
> fuel diaphram. The engine ran perfectly for two mowings but the next
> time it absolutely refused to start at all. I inspected the plug which
> was very wet so took another look at the diaphram and fuel filters which
> seemed OK. Checked for a spark at the plug, which also seems OK so I
> tried to check compression. Following a suggestion I found elsewhere on
> the web, with the plug lead off, the engine brake lever tied to off
> position, I turned the engine backwards. I could feel resistance at one
> point but after turning it past that, it took two whole turns before it
> resisted again.
> I would be really grateful if anyone is able to tell me if this is
> normal, or indeed make any other suggestions as to what the problem
> might be.
> Many thanks.
During one of the piston travels the exhaust valve will be open, so if
its being reversed that sounds right.
NT
Posted by Anarchy on September 11, 2011, 4:11 am
> wrote:
> > I recently had the common problem of engine running rough, puffs of
> > black smoke etc. It had been used for four seasons with no maintenance
> > whatsoever so I changed the oil, fitted new air filter, spark plug and
> > fuel diaphram. The engine ran perfectly for two mowings but the next
> > time it absolutely refused to start at all. I inspected the plug which
> > was very wet so took another look at the diaphram and fuel filters which
> > seemed OK. Checked for a spark at the plug, which also seems OK so I
> > tried to check compression. Following a suggestion I found elsewhere on
> > the web, with the plug lead off, the engine brake lever tied to off
> > position, I turned the engine backwards. I could feel resistance at one
> > point but after turning it past that, it took two whole turns before it
> > resisted again.
> > I would be really grateful if anyone is able to tell me if this is
> > normal, or indeed make any other suggestions as to what the problem
> > might be.
> > Many thanks.
> > --
> > GodfreyY
> Though the spark plug looks wet, it could be oil not fuel. If it won't
> dry out when left a while, it is oil. Oli can kill the spark, stopping
> it from running.
> This usually indicates a worn bore/broken piston ring. Does it use a
> lot of oil or does the oil get dirty very quickly?
> If the air filter is clean, then most other problems revolve round the
> ignition system.
> There may be points (depending on the technolgy) that need cleaning/
> adjusting.
> More unusually, HT lead spark plug connector/cap.
> You will only feel compression on every alternate revolution. If you
> can feel it, the engine is usually mechanically OK, though sometimes a
> ring can still be broken.
Rather than posting all this misleading info, would it not be better
for the OP to simply try fitting a new spark plug, and see if that
sorts his problems?
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>black smoke etc. It had been used for four seasons with no maintenance
>whatsoever so I changed the oil, fitted new air filter, spark plug and
>fuel diaphram. The engine ran perfectly for two mowings but the next
>time it absolutely refused to start at all. I inspected the plug which
>was very wet so took another look at the diaphram and fuel filters which
>seemed OK. Checked for a spark at the plug, which also seems OK so I
>tried to check compression. Following a suggestion I found elsewhere on
>the web, with the plug lead off, the engine brake lever tied to off
>position, I turned the engine backwards. I could feel resistance at one
>point but after turning it past that, it took two whole turns before it
>resisted again.
>I would be really grateful if anyone is able to tell me if this is
>normal, or indeed make any other suggestions as to what the problem
>might be.
>Many thanks.