A new acceleration test was introduced for USA and from memory the test was 40 mph snap open throttle in top gear, this was fine without the mutes fitted, but with the mutes ( small disk fitted to the end of the exhaust silencer ) , this caused a the muted condition, ..............................the final cure was to install a cut away spray tube, this allowed a much smaller main jet to be used this in turn stopped the eight stroking when trying to pass the USA acceleration test, think 40 to 60 mph in a certain time.
It is not difficult to see how this worked, FOR THE MUTED CONDITION
Most times with the mutes fitted we would snap at the 1/4 mile point at 30 and 40 mph and be doing the same speed, 30 or 40 mph at the timing lights, after 1/4 mile, of course you could feather the throttle back and judicially pick up speed and improve, but the idea was that a person when accelerating passed a long vehicle could not be expected to intervene and should expect a solid reliable acceleration.
You may not be aware that AMAL did not set up the Carburettors for the trade, BSA, TRIUMPH, NORTON but development worked closely with Amal, and the responsibility for final sign off and payment was down to the Test and Development department of each of the firms, as Deputy group test rider under Bob Mann's we carried such responsibility........
One final thing that would vindicate the modification was the fact that we had over 150 bikes held up and not allowed in California test Authority, and after the modification they and all subsequent Nortons passed straight in.
I am not sure if Alan Lines? of Amal is still alive but he would no doubt give ....chapter and verse on how and why the cutaway spray tube was beneficial to the MUTED CONDITION.
Regards
Bob Rowley
