I've only ever had to replace a distributor cap or rotor once in 40 years,
including several cars that have done up to 75k miles. Nevertheless you
could have a problem with the rotor or cap, and the way to diagnose this is
with a timing light. Clip it onto each plug lead and the coil lead. If the
flashes on the coil lead are steady and regular whereas those on one or more
plug leads seems to miss one that coincides with the misfire, the rotor
and/or cap are suspect. Hardly worth diagnosing which, it would be better
to replace both, but FWIW if the miss happens on any plug lead it is more
likely to be the rotor, if only on one or two then probably the cap. The
condenser could also be suspect - the symptom of this is a weak spark, if
you ease the coil lead out of the coil with the engine running it should
*continue* running with a sharp 'crack' - 'crack' from the air gap between
the coil terminal and coil lead before eventually the gap gets to big for
the spark to jump. Always eliminate any potential ignition problem before
looking at fuel. You should also check plug condition and gaps are OK,
dwell and timing correct and steady, plug lead condition satisfactory, etc.
Another one I would check is the condition of the LT coil lead as it goes
into the distributor and the ground wire inside the distributor. Both these
are subject to flexing from changing engine vacuum when you operate the
throttle pedal, the ground wire can get visibly ratty and frayed, and the
coil wire conductors can go open-circuit inside the insulation. Problems
here can cause cutting-out when accelerating.
Like-wise the SU fuel pump is very long-lived and reliable. Of course the
points on the original type do eventually fail, but usually that causes the
pump to stop pumping altogether - which can be temporarily 'repaired' to get
you home with a sharp rap. My V8 came with an SU-type pointless conversion
and it was OK for a few years but then started short-stroking which caused
fuel starvation. Unlike the points type there is nothing you can do with
this 'pointless' type, you either have to wait for it to start working
properly or junk it. After having been stuck for a while three times with
the former strategy I adopted the latter strategy and replaced it with a
refurbished points-type and have had no more problems. If you remove a fuel
feed pipe from a carb and direct it into a container and turn on the
ignition, it should deliver *at least* 1/2 Imperial pint per minute with the
pulses regular and consistent and few if any bubbles.
And yes, any MG prefers to be driven, but problems of this nature are due to
a defect rather than low usage.
PaulH.
----- Original Message -----
> While driving my 1974 MGB recently, the engine would sputter badly and
> sometimes stall when taking off from a stop...
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