I have a tricky problem I have been having a heck of a time diagnosing, and
I hope someone can offer some help. I have a stock '68 1600 that misses,
but only under a load, and usually only from 2250-2900 rpm (so right about
55mph). The missing tends to clear up when the engine gets above 3000 rpm.
Note it runs perfectly and revs perfectly when not under a load. The car
feels like it loses about 1/3 its horsepower, like it is running on 2
cylinders.
Work Done:
So far, I have gotten the carbs adjusted and balanced by a local "z"
specialist shop, got the timing curve adjusted on an osciloscope, and
replaced the coil and coil resistor, thinking they may be breaking down.
The points, cap, rotor, plugs, and plug wires are all new. The valves were
also just adjusted.
Today, I went out and bought a cheapie fuel pressure guage, and mounted a
pickup for it in the line between the two carbs. I noted that the fuel
pressure stayed about 4psi when it was running right, but fluctuated wildly,
from 3-5psi when the car was missing. The needle really jumped around
during this time..
Does anyone have any ideas? I am guessing I may have a pressure regulator
problem, but is the regulator located in the fuel pump or is it the gizmo
located on the fuel line on the back carbureator right where the fuel line
goes into the rear carb? Could I have a problem with the float settings on
the carb? Is it still likely something in the ignition? I think the
ignition is ok, as it has all been replaced or checked in the last month.
Thanks for all the help. If needed I can take a few pics...
-Joe
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