Puzzling Lawm Mower Problem

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On Jun 17, 3:32pm, snipped-for-privacy@carploin.com wrote:

check for spark at plug. pll plug wire off in broke condition and see if another plug has a spark.
if it sparks good in broke condition add some gas to the plug hole and try starting mower.
theres just 3 possibilties, no spark, no compression, or no fuel.
along with a 4th possible.
the starter is going bad and cranks the engine too slow, but pulling cord frees things up a bit allowing it to start with key.
if the battery is 12 volts try starting it in the broke condition with a charger attached
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On Sunday, June 17, 2012 3:32:36 PM UTC-4, (unknown) wrote:

Not sure that's the case. When you pull very slowly, there is no resistance. You are clearly not pulling against compression. I'm not sure what the mechanism is, but some speed is required to lock up and spin the engine. Is there a centrifugal clutch, maybe?
I know that doesn't help with the diagnosis, but it might spell the difference between the rope pull and the key start.
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On 6/18/2012 2:22 PM, TimR wrote:

When pull very slowly valves don't close rapidly enough to build much compression so don't notice it (much). That also gives somewhere for the vapor to go if it is vapor lock.
--
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I don't THINK you have a real case of vapour lock, since there is no fuel pump. Fuel boiling out of the carb and "dry flooding" the engine is a possibility (mixture too rich to light) and turning the engine through slowly by hand COULD be moving enough air through without drawing more fuel like it would with a fast enough crank to try to start the engine.
Pulling the starter rope turns a "sprague clutch" that catches the flywheel (using different mechanisms on different engine - ball bearings in a race on some old Briggs engines, steel tabs on some others - and likely several I've either forgotten or never seen) which turns the motor. MOST small engines in the last 40 years have some sort od "compession release" which either holds a valve open or closed below a certain speed to allow the engine to be spun up to starting speed easily. When up to speed the compression release goes off, allowing full compression, which starts the engine.
The ONLY thing I can see hand cranking the engine slowly acvcomplishing is diluting the charge in the intake and cyl by moving air through the system.
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On 6/18/2012 5:23 PM, snipped-for-privacy@snyder.on.ca wrote: ...

...
Well, there is a fuel pump, it's the diaphragm/spring in the carb...
One I've spent today playing with...392/432 and 390 w/ pinhole in diaphragm. That way it doesn't do too good... :)
But yes, if it is as I've suggested it is as you describe that's going on--and the name seems as good as any for discussion purposes here.
I've seen it on one B&S and while it didn't have electric start to have a symptom just as the OP's, cooling it down would work which is how I came up w/ the foil and a heat shield idea that (pretty much) solved it.
--
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Except I BELIEVE this mower has a Tecumseh engine on it, which uses a gravity feed float type carb with NO pump and NO diaphragm., And therefore NO chance, technically, of a vapour lock.
see: http://www.partstree.com/parts/?lc=toro_consumer&mn 018%2C+22%22+Recycler+Lawnmower%2C+2002+(SN+220300001-220999999)&dn329_334-_3340012-0009
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On Jun 18, 10:14pm, snipped-for-privacy@snyder.on.ca wrote:

its one of these........
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snipped-for-privacy@snyder.on.ca wrote:

Hmmm, If it is too ruch(flooding), could smell it. No?
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wrote:

Usually - a wet flood for sure, but a "dry flood" perhaps not.
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One other thing to try, if you are reasonably handy, is to hold the throttle butterfly wide open when cranking with the starter to see if it starts then. Be ready to release control to the governor as soon as it starts. If this s tarts the engine, it IS flooding. Perculation of the gas in the carb will do this - known as a "dry flood" - and a leaky float valve or excessively high float level can cause a "wet flood" - which is harder to clear and will give you a wet spark plug if you pull it to check when it is in "no start mode"
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