Do you mean it won't crank (cranking is generally taken to mean that the
engine is turning over on the starter) or it cranks on the starter but won't
fire up? I suspect the latter.
Is the tach erratic in time with the misfire? If so suspect an ignition LT
fault i.e. bad connections in the 12v feed to the coil, bad coil (OK, youve
changed it), bad wire from coil to points, bad points, bad ground wire in
distributor, bad condenser. The ground and points wires can break inside
the insulation inside the distributor because the base-plate flexes under
vacuum and twists them. Hmmm, wonder if that was why the PO disconnected
the vacuum.
If not suspect HT or fuel problems.
Your best be is to do some testing when it will crank but not fire. Check
the voltage on the coil +ve - it should vary between 12v and 6v as the
points open and close respectively. Check the voltage on the coil -ve - it
should vary between 12v and 0v (ground) again as the points open and close.
If that is OK the ignition LT looks OK.
Now put a timing light on each plug lead in turn and watch it while
cranking. Does it flash regularly on each? Hold each plug lead
(carefully!) away from its plug and see just how far the spark will jump.
You should get at lesat 1/4", blue, and with a sharp 'crack'. If so the HT
is probably OK. If it's short, yellow, and fizzes it's probably the
condenser, its possible for these to break down under heat (like a coil, or
bad connections) with heat and repair again as it cools. It's unlikely to
be timing or points or plug gaps given your symptoms, and I note you have
replaced the plugs any way. What gap did you use? Did you replace the
points? What gap on those?
Only have experience setting-up SUs but it is quite easy to do these without
an analyser, there is info on this on the web site below, select 'Spanners'
and 'SU Carbs'. Also 'Ignition' info.
PaulH
http://www.mgb-stuff.org.uk
----- Original Message -----
From: Greg Bass <gregbass@atlantadental.com>
To: 'Greg Bass' <gregbass@atlantadesign.net>; <mgs@autox.team.net>
Sent: Wednesday, May 16, 2001 7:57 PM
Subject: RE: testing... HELP NEEDED!!!! PLEASE!!!
> I have a '78 B that continues to run rough. It started with a fluxuating
> idle and some sight missing when at speed (ok, ok... speed may not be the
> relative term in a B :-). Then it progressed to a point where it would not
> crank for a hour or so after shut down. I have changes the coil, the
plugs,
> the pug wires, reset the points (yep it is not an electronic dist) rebuilt
> the carb, reset the choke and the idle speed, verified and reset the
timing
> to 10 degrees BTDC, reconnected the crank vent tube to the carb,
reconnected
> the vac advance to the dist (both of which the PO had removed. Why?),
tried
> to set the fuel/air mix without an analyzer, but I don't think I have that
> even close.
///
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