>Reading Spark Plugs
>
>Hi Folks,
>Here's an interesting little topic. ( Well I think so anyway)
>Is it possible to "fine tune" your carb mixtures by looking at the
>condition of your plugs? If so, here's some questions:
>A recent post said that the outer plugs (#1 and 4) tend to run rich, at
>least on an MGB. Does this apply to a Midget and if so , why?
>If the engine was burning oil or if there was a slight ignition miss on o=
>ne
>or more cylinders, wouldn't this confuse the issue. =
>
>Is it OK to use a brass wire brush to clean the plugs.
[snip]
>Adrian. (Being an old fart sure beats the alternative!)
First fix the oil problem.
With a healthy ignition system, (good plugs, cap, rotor and wires), you
will find that one or more of the end cyl. will run rich. This really
has to do with the head and intake design. I'm sure you have the same
intake that is on my '73 which is nothing more than a tube with ports on
it. As the A/F (air/fuel) mix flows straight through an intake there is
little problem. The farther it has to travel the more of the fuel is
going to settle out of the A/F mix. Add to this the fact that the end of
the intake is a dead end being nice and flat and causes a disruption in
the flow of the mix. These main points, plus a couple of minor ones,
cause a fair amount of liquid fuel to enter the cyl. This liquid they
mostly evaporates during the combustion process and burns with the
already present and hopefully correct ratio of A/F mix. The result is a
single cyl.(s) that end up running rich. This is a problem for any motor
that is NOT running a single venturi for each cyl. or NOT a MPI(multi
port injection) or SFI(sequential fuel injection) engine.
Bob Allen Replied:
>> JC Whitney has something that uses grit and is powered by the car battery.
>> Cost $8. Anybody used it?
>
>Spark plugs get worn out for two reasons. One is all the crap that gets
>deposited on it that you might be able to clean off. The other is that
>the elctrode gets worn with rounded ends. This is a bad thing as the
>spark is easier to control (timing) when the spark can launch off the
>sharp corners of new plugs. The Plug Sandblasters just wear out the
>plugs faster due to problem number two.
Bob has it. Just to elaborate... the spark is supposed to come from the
corner of the electrode and NOT from the center. This is why the needle
type of plugs like the Bosch Platinum give consistent performance over
their lifetime as they wear--the spark always has a concentrated launch
point.
On a side note: Plugs with a modified burn pattern like the Splitfire
plug that cause the initial burn from the spark to also extend straight
away from the plug are not a good idea. Manufactures have been designing
the compression cavity and head dome to get the best burn pattern using a
conventional style plug for many years. This is the key point in modern
efficient engines. These so-called wonder plugs actually cause
incomplete burn patterns in autos.
John Knight '73 MGB (under restoration)
"If uniqueness makes us who we are, why be like everyone else?"
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