On Jun 17, 3:32 pm, firstname.lastname@example.org 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
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.
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.
On 6/18/2012 5:23 PM, email@example.com 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.
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.
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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