New Bosch Ignition Coil Installed
(I also posted part of the wiring diagram showing the external resistor and coil - from www.311s.org, a good resource site for roadster restoration)

Finally, I was able to have the new Bosch coil installed along with its (very very important!) external ballast resistor. I also had the carburetor calibrated again to smoothen out the backfire problems at idle. The mechanic also used a dwell meter, which he attached to one of the high-tension wires leading to one of the spark plugs. Initial readings on the meter show that the dwell is only at 38-39. This explains why the engine has been misfiring at high rpm. So the mechanic adjusted the cam angle to 45 (the optimum range for dwell is from 40-50 as explained by the mechanic). During the road test, I noticed that engine response and torque did improve, which resulted to better shift points. Driving the Fairlady is much easier and predictable. I don't have to change gears (usually 2nd and 3rd gear in traffic) often to prevent the engine from sputtering. Now the roadster is much better to drive and "very" tempting to test to the limit :)

Last night I was able to test the reliability of the newly installed Bosch coil and so far no problems even at low rpm where there's a tendency for these kinds of coils to heat up rapidly. I think the resistor is doing its job preventing the coil from overheating during idle :) But I'll be keeping a spare ignition coil just in case...