Vance,
Thanks for the suggestions. Please see the answers to your questions below:
I am still struck by the fact that only the number one cylinder
is having issues.
[Dave] It turns out this was misleading information. Other cylinders show
the same timing jump but at a much reduced occurrence rate. I had to wait
almost 5 min to see the same result with #6.
1. What are you setting your point gap to?
[Dave] Gapped as per Bentley.
Have you tried increasing the gap a bit?
[Dave] Yes, no improvement.
I am thinking that perhaps you dizzy has a
flat lobe for the number one cylinder, and so the points are getting
opened enough to fire the number one spark plug.
2. Are you using any sort of electronic ignition? A pertronix
perhaps? Something that uses little magnets to fire each plug? one of
the magnets might be weak resulting in intermittent firing of the number
one plug.
[Dave] My original ignition was a Crane XR700. When starting the new motor
and running in the cam my mechanic used points; once we got the car on the
dyno we also tried the XR700 and a Petronix unit. All showed the same
symptoms. This is when we swapped distributors. We found a crack in the
housing of the original dizzy and more play in the 2nd dizzy and so combined
them to make one "better" unit. Since this comprised of my old innards and
the "new" housing it is possible that the dizzy is still the culprit. I
have ordered a Mallory Unilite dizzy to see if I can put this to rest.
Unfortunately the TBI setup still to go is not compatible with the Unilite
so I still will need to get this resolved using a stock dizzy.
3. Are your valves opening on the number one cylinder? Could you
have a flat lobe or misadjusted rocker on that cylinder so that the
compression is low or the cylinder is not drawing in enough air/fuel?
[Dave] This was also one of our concerns. We measured valve lift to see if
we lost a lobe (did not want to pull the cam unless there was some
indication) and all measurements were within a couple of thou; likely within
the margin of error of the fools doing the measurement :)
As I recall you have swapped the wires, plugs, and dizzy cap,
and swapped rotors for the dizzy.
4. Is your dizzy shaft worn? Can you wiggle the dizzy rotor from
side to side? If so, then the cam that activates the points may be moving
enough to avoid opening the points to fire the number one plug.
[Dave] There is minor rotational play but no discernible side to side play.
The new dizzy should address this possibility.
5. Are you certain that drive gear (in the block under the
dizzy) is in correctly? The slot in the top of the dizzy drive gear is
not symmetric, and if you get it in backwards the dizzy will not seat
fully, and your dizzy drive shaft can wobble. Try having a friend crank
the car while you watch the dizzy rotor (cap off). Does the rotor
wobble?
[Dave] Drive gear is installed correctly. We actually tried 3 different
ones to see if excessive wear in this component was causing the problem.
Did not see any wobble with any of the drive gears.
Cheers,
Vance
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