Could be almost anything, especially since you have recently worked on
ignition and carbs. What does the tach do for a start? If that is flicking
all over the place then it is an ignition LT problem. If it is relatively
steady then HT or fuel. As it happens when cruising you may be able to
reproduce it with your head under the bonnet, if so clip a timing light onto
the coil and plug leads and watch the flashes. Erratic flashing on the coil
lead indicates coil or possibly condenser problems. Steady on the coil lead
but irregular on the plug leads (remember the coil lead flashes four times
faster than any one plug lead) indicates that the rotor or cap are breaking
down, although that would be more likely under acceleration than cruising.
While on No.1 lead point it at the timing marks to check that it is about
right, and not jumping around. If all that is OK then it looks like carbs.
Unlikely to be fuel starvation as that would be worse under acceleration.
Could be the aforementioned vacuum leak, test with propane or carb cleaner,
or possibly float valves, a slight leak causing mixture problems under light
fuel demand but not under heavier demand. If you have an SU pump turn on
the ignition but don't start the engine, and listen to the clicks. Once the
float chambers have been filled the pump shouldn't click more than once
every 30 secs. More than this indicates a leaking float valve or possibly a
leaking one-way valve in the pump inlet, although this latter is more likely
to cause problems under high fuel demand than low. Remove the float chamber
vent pipes to see if one or other carbs does eventually start to overflow,
this can take several minutes, so disconnect the coil to prevent it
overheating.
PaulH.
----- Original Message -----
> ... The spitting issue was much worse coming home. Essentially,
> after a half-mile of steady speed cruising, she would start this pop-
> pop-pop shutter. If I were climbing a hill, or accelerating
> moderately, no problems. I've recently set the timing and set the
> carbs.
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