[Mgs] sputter

Paul Hunt paul.hunt1 at blueyonder.co.uk
Mon Jul 13 04:50:21 MDT 2009


Ignition problems often show up as fluttering of the tach needle if it is the
LT side e.g. coil, points or connections.  If that is steady with actual
engine speed then ignition HT or fuel.  A misfire under load could be either
HT or fuel, but if HT it will happen immediately, if fuel it will only happen
after a delay i.e. when the float chambers get low if it is a problem with the
supply i.e. pump.  With the original SU pump it is useful to switch off when a
misfire or cut-out occurs, then when the car has come to a stop and you can
hear the pump switch on again.  If you hear the pump chattering away like
billy-oh then it *was* fuel starvation.  If not, and the car then proceeds to
start and drive normally, then probably HT.  The pump should deliver a minimum
of one Imperial pint per minute and in practice closer to two, with a pipe
removed from a carb and directed into a container and the ignition turned on.
An SU pump should operate with a steady series of pulses and minimal bubbles.
HT problems will often show themselves if you rev the engine hard (not massive
revs, but full throttle for a short pulse) with a timing light connected to
the coil lead and each plug lead in turn.  If the flashes stop or get erratic
with a misfire then it is HT.  If on one or more plug leads but not the coil
lead then it will be cap or rotor, if on the coil lead as well then the coil
or other ignition problem.

PaulH.

  ----- Original Message -----
  I have a 74 B that has a irritating problem. When at highway speed, not
around town , I get this period loss of power, ...


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