I owe everyone that responded on this question a reply, a thank you, and
a follow-up on the solution.
I had numerous responses, most of which questioned my fuel mixture or
centered on my condensor or coil.
Thanks to all of you for those responses, but as it turns out, it was
none of those things.
The problem became more definitive when the "high rpm miss" turned into
"no rpm at all."
I was driving to work in the MGA with the idea of continuing on for a
Hill Country tour that weekend. The miss became really bad about half
way. Then the motor started cutting out altogether. I managed to pull
over and get it running again by fussing with the distributor cap and
ignition wires, although I couldn't pin down the problem.
It cut out a couple of times more on the way back home (I had turned
around by this point) and finally completely died. A quick check
revealed that there was no spark at #1 cylinder. I got a tow home.
The car dying altogether was actually fortuitous, because now I could
positively identify the problem as being an ignition issue. Previously,
the intermittent nature of the thing made it hard to pin down. Also,
since I had swapped out condensors, cap and wires, and coils, I had
previously rulled out the ignition system.
There is a clue there, by the way, that might tell you what I eventually
found.
That weekend I got out the shop manual (Haynes) and went through the
troubleshooting steps for "no spark." I checked the points, condensor
(swapped with third, working when removed, condensor), and various
current flow points as instructed. I then checked the coil for spark by
removing the high tension coil wire from the distributor and holding it
near the block. Since I got spark there, it was obvious that there was
still a problem in the distributor. The book said that it had to be
either the cap or the rotor since all the other checks had been run.
Since I had swapped out the cap before, I tryed the rotor. The rotor was
new, as were all the other ignition components. I swapped it with an old
one I had lying around. Eureka! I now had spark at #1! Just to make
sure that was my problem, I replaced it again with the original rotor.
No spark at #1. I had finally found my problem. I put the spare rotor
back in. No more missing.
The bad rotor looks OK on visual inspection and those things are so
simple it is hard to imagine how they could be bad right out of the box.
I did detect a little play in the metal piece, but not very much. There
might be some sort of crack in it which causes it to ground out.
Thanks again to those who responded.
BTW, the Hill Country tour was canceled anyway because of torrential
rains...
David Littlefield
'62 MGA MkII
'51 MGTD
'74 MG Midget vintage racer
'88 Jaguar XJ-S
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