Mike Stevenson writes:
>Listers,
>Some time ago on the Stag list, I asked a general question about
'blipping'
>the throttle just before switching off the ignition. I would be
interested
>in the wider classics view. Briefly, since I was a kid, I was told to
blip
>the throttle at shutdown so that the bearings would be primed for the next
>start and the float chambers would be full if a mechanical fuel pump were
>fitted. The opposite view is that the extra fuel entering the cylinders
at
>shutdown would wash the thin film of oil lubrication from the walls and
lead
>to excessive friction and wear.
>Does anyone out there still do it? Do we have any more reasons for and
>against?
>Regards,
>Mike
>'71 Stag
>ex '56 MGA
Mike,
Here's my take on it:
On early models running the engine up and switching off is not good for
the reason you cite; when the key is switched off the ignition stops
functioning but the carburettors continue to intruduce fuel in the
airstream leaving much unburned gas in the cylinders and the exhaust
system. This rinses the oil from the side of the cylinders and puts
unburned hydrocarbons into the atmosphere. Of course the wash down
effect is minimal since the rings wipe most of the oil away anyway.
In the mid 70's BL fitted most cars with the Anti-run-on system to
eliminate dieseling. This system (discussed on this list to great
length) cuts off fuel flow when the key is switched off. And, of
course, the electronic fuel injected systems shut off fuel flow when
the key is switched off. On these models bliping the throttle will
allow the engine to wind down drawing nothing but fresh air through
the engine. What the advantage is to this escapes me.
As far as filling the float chambers; if your fuel pump is having
trouble keeping up with fuel demands at idle then you need a new
fuel pump. As far as priming the bearing: if your oil pump is having
trouble keeping your bearings lube'd at idle you need a new oil pump.
Or new bearings. Or both.
But if it makes you feel good, do it.
Dave Massey
St. Louis, MO USA
57 TR3
71 TR6
80 TR8
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