[NickRCarter]

Its taken a time for the weather to allow me to play. I checked the linkage, as far as I can see the secondaries are prevented from opening until the throttle is advanced about a quarter open, then they are free to move, being closed again by the closing of the throttle linkage. Other than that the secondaries are free to move.
I have replaced the quick change top back to stock and installed the yellow spring. I was also able to check the vacuum passage to both primary and secondary venturis by use of a stethoscope made from a length of small diameter rubber hose and operating the actuating rod before reconnecting to the secondary spindle.
Out on the road its performing much better with a 0-90mph time of 14 secs although it should be better than that. I also found that the secondaries are now opening but only about 1/4" on the actuating rod. So not quite there yet.
Nick