If you have a Gen II FJR and want to have best odds of a functional cruise install and ~$600 or more doesn’t matter to you the MC unit is the way to go. The AVCC is inexpensive (as opposed to cheap) and when it works, it works quite well but there seems to be a high number of Gen II installs that fail when hot.
I'm guessing that AV doesn't provide any type of schematic of the unit.
I think that the problem is in the tach pickup lead. Since they only use a a 20k resistor as the filter, I would try some inductance as close to the controller as possible, an easy way, if you have extra lead, would be with Radio Shack 273-104 or if you don't mind soldering (or just wire nuts to try it) 273-102 in series with the tach lead.
You may actually need some resistance and capacitance to ground on the tach lead as a filter, that's why I'd like to see the AV circuit diagram.
Some thoughts about the failing AVCC units:
Since the majority of the AVCC problems are reported as speed sag and not abrupt shut-off, that should rule out the brake circuit, power circuits and gross tach signal read errors.
I agree that the speed sag failure symptom is consistent with a coil signal read error. I had suggested that some intrepid soul use the magnetic pickup in place of the tach tap as a diagnostic tool. At least one person wrote back to say that with the magnetic pickup they still had the same failure when hot. I dunno, guess we have to assume they actually did the mag signal and they accurately reported the results. If the problem was resolved by substituting the tach signal with the magnetic pickup there could be a number of ways to resolve the problem. The first best way would be to build a ' non-retriggerable one-shot' circuit to buffer the tach signal, followed by modifications to the stock AVCC 'filter'.
I suggested that someone tee a vacuum gauge into the line going to the AVCC servo which another person says they did and the vacuum was adequate, though the vacuum levels they reported were not in the range I would have expected.
I suggested that someone try measuring the force needed to move the throttle bell-crank and see if some of the problem installs required higher than normal(?) force. No feed back on this one -- has anyone that's having a problem already released the throttle spring?
Since Smitty has done a ton of these installs I think it is safe to say that the installs were done essentially the same. Just to review, the dip switches were set for light vehicle, high power and correct number of cylinders? The servo unit itself is solidly anchored? The servo throttle cable is securely anchored close to the throttle bell-crank? The bell-crank attachment doesn't bind when heat expands the parts? If the control pad was sealed, is there a possibility that the Coast button is inadvertently being activated?
I found this 
