Hi All,
I have had a similar problem since the car was new. Yes, in the beginning I did some things wrong but learned over the past 54 years and still idle at colse to 1K RPMs. During the time, I have increased compression by requesting (incorrectly) the head be shaved 0.060 instead of the 0.006 I should have had. However, this has proven a benifit and did add some additional umph. I use a minimum of 93 Octane fuel and higher; when economically available, to eliminate pre-ignition and also tend to set the carbs a bit rich. I dynamically balance the carbs and set both carburetors as close as possible with 2 Color Tune units (each fixed-attached to a carburetor). Last, I have a Crane electronic ignition and use an adjustable timing light to dynamically set the timing at 15 deg. BTDC. Again, with all this, I can't seem to get a smooth even idle under 1K RPMs but can briskly accelerate and the engine winds freely to 5K+.
Recently, a friend who had a similar problem suggested I try one more thing. It seems he brought his Healey to an experienced tuner who had achieved a smooth even idle on his car for the first time at close to 600 RPM. Curious, upon investigation, he found that the carbs differed from his setting in only one condition, the pin step was not even with the bottom of the piston but set about 1/10" deeper.
Since his HD8s are standard BJ8 carburetors and I am not sure what this change would do to idle performance. However, I will be trying to find out within the next few weeks.
Ray(64BJ8P1)