Here are a few more guesses.
1. Check the small wire inside the distributor. It has to be flexible
to allow the contact plate to rotate for vacuum advance. After many
years the flexing causes strands to break inside the insulation so it
*looks* OK but can have an iffy connection.
2. Look for a crack in the rotor and inside the distributor cap. Look
closely - even a scratch can cause problems.
3. You don't mention replacing the spark plug wires. Sometimes with
old wires the insulation breaks down and the electricity 'leaks'. I've
looked at engine bays at night (i.e. in the dark) and seen the wires
arcing all over. I've also experienced 'ignition crossfire' in our
Alfa. Try routing the wires so they are not parallel for any length.
4. My first thought was a bad coil - they often begin to fail when the
engine gets warm - I assume due to heat. Do you have the old coil? Was
it working OK before all the work you did? If so, try swapping it back
in.
5. Recheck your carb adjustments. What do the spark plugs look like?
Maybe it starts OK because the mixture is rich then fouls the plugs
when it warms up. Or maybe the mixture is too lean and starts OK with
the choke pulled out then is misfiring after it warms up & the choke
is released. Try pulling out the choke when it is misfiring. If it
improves then the mixture may be too lean, if it worsens it may be too
rich. But check everything else first - most "carb problems" are
ignition related!
Eric Russell
Mebane, NC
http://home.mebtel.net/~ejrussell
----- Original Message -----
> Date: Fri, 21 Jul 2006 13:12:47 -0400
> From: "Sam DeSalvo" <sdesalvo@frontiernet.net>
> Subject: MG misfire
>
> My '52 MGTD Mark II runs fine on startup. After it warms to
> operating temp, it
> starts misfiring to the point where it stops running. I just
> installed a new
> coil, have rebuilt the head, adjusted the carbs, timing, points.
> Does anyone
> in MG land have a clue what the problem could be? Clogged exhaust?
> Distributor? Any ideas would be appreciated.
> Thanks,
> Sam
> TD
> BN1
> MGB
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