At 08:38 AM 11/13/2000 -0500, wtsnyder@juno.com wrote:
>My 66 MGB .... the starter turns VERY slow when the ignition switch is
"on", and fast (normal) when the ignition switch is "off." ....
Too much spark advance causes it to fire and kick back before it gets to
top dead center. Check the timing. Try retarding it a bit; turn the
distributor body a few degrees clockwise.
>....
>.... not firing on the first cylinder, and is fitted with Mikuni Carbs. ....
>
>.... Compression checks out at 100-120 on all cylinders. .... When the
engine is running and the first plug wire is removed, no change in running
is noted. When the plug is left on the wire and grounded, good and regular
spark is noted. When the #1 plug is removed after running, raw gas is noted
on the plug.
Compression, fuel, and spark, but still no fire? Ah, I love a challenge.
>**When the #1 plug wire is removed from the plug, spark can be seen
escaping around the distributor cap. .... The escaping spark is not noted
when the plug wire is connected.
>....
I got it. Spark should never escape from the dizzy cap, not even when a
wire is removed from a plug. Indication here is a bad dizzy cap, or at
least a bad seal where the wire boot sits on the cap. This condition can
also be aggrevated by a high resistance spark plug or a high resistance
plug wire. You get a spark with the plug out and grounded because there is
not much resistance at the plug tip, and the spark jumps there easier than
the longer distance across the dizzy cap. When you install the plug and
start the engine there is high compression in the cylinder which increases
the resistance across the plug tip rather dramatically. The spark then
finds an easier path across the top of the dizzy cap to ground.
The reason you are not seeing the spark on the cap with the engine running
could be because the spark plug is draining off some of the energy, just
not enough to get sufficient power to ignite the fuel, and the remaining
energy being wasted arcoss the dizzy cap is insufficient to make the spark
there visible. You might try this again in the dark to see if the spark is
then visible across the dizzy cap. My guess is that you need either a new
distributor cap or new plug wires (or at least new rubber boots), or maybe
all of the above.
If you don't like spending money replacing good parts you should
investigate further to determine which part is (parts are) at fault. Start
by switching the #1 plug with one from a different cylinder. If the
problem moves to the other cylinder it's a bad spark plug. Otherwise try
switching the #1 plug wire with one on a different cylinder. If the
problem then moves to the other cylinder it's a bad plug wire or the rubber
boots on the plug wire. If doing these things has no affect, and the spark
still arcs across the dizzy cap under the same conditions, then it's a bad
cap.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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