Firstly is the tach steady, other than changing as the revs change, when the
engine is running badly or is it flicking? If it is steady you can forget
the ignition LT, if not check coil, points, condenser, distributor and
connections.
Secondly, since the problem seems to happen when idling or revved, connect a
timing light to each plug lead in turn and point it at the pulley, 1 and 4
will be on the timing mark and 2 and 3 will be 180 degrees different, put
another mark this side. You are looking for two things - irregular flashing
or big variations in timing that coincide with any stumbling. Irregular
flashing indicates an HT problem, variations indicate a distributor problem.
HT could be leads, cap (any flashes when viewed in the dark?) or rotor,
which tie in with cold/damp conditions. My daughters car had a similar
problem, showed an erratic HT at the plug leads, but a steady HT on the coil
lead. This indicated the cap or rotor were breaking down, changing both
(you might as well rather than diagnosing further) cured it.
If the HT at the plug leads is steady and regular it must be fuel, so after
a bit of rough running check the plugs and see if some are wet and some are
dry. If it were running rich using no choke when cold would clear it, and
rich mixture gives a rhythmic effect rather than irregular. You can see
this by, when it eventually warms up and idles smoothly, pulling out the
choke for a few seconds. As far as seeing smoke when lights are behind you
this is probably just an optical effect of lights through normal exhaust
fumes, particularly if you can't see it in the day time or when you go round
the back. I've seen the same effect with my car when backed up to a white
garage door in bright sunlight from right in front and above me, I could see
what looked like clouds of smoke (from a previously clean engine) against
the garage door but when I jumped out and walked round the back there was
nothing. Check the float valves are working OK by switching on the ignition
without starting the engine, if you have a SU pump it should click a few
times and stop, then click less than once every 30 secs. If it clicks more
frequently, or you have a continuously running aftermarket pump, disconnect
the float chamber overflow pipes and see if any fuel is coming from the
ports.
PaulH.
----- Original Message -----
From: "Paul M." <rowman22001@yahoo.com>
To: "Max Heim" <mvheim@studiolimage.com>; "MG List" <mgs@autox.team.net>
Sent: Thursday, December 11, 2003 9:53 PM
Subject: Re: MGB running problem
> Also, when driving at night, if there was someone
> right behind me with their lights on, I could see some
> light smoke when I'd go to full throttle. Nothing
> major, and nothing I could see during the daytime, but
> it was there, and so I figured the car was rich.
|