Tech session went as scheduled with a few participants. I offered a session on the 850 balanced piped exhaust VS Amal carb cut away spray tube.
It was discussed on access norton to some great length. However I did not agree with some of the assertions that did not have technical merit.
It ended after 161 posts
I've supplied the link here:
www.accessnorton.com/NortonCommando/mkii...vs-peashooter.23436/
Folks were side tracked by peashooter/mute discussion where in reality the balance pipe is the origin for low level leanness to be cured.
OFFERED AS DATA:
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, I 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
My analysis is that the "snap open with mutes" would put it way to rich when above the cutaway onto the needle.
A cutaway spraytube would retain the low end richness(needed for the balance pipes) and the 4 groove (lean) needle would cut down the higher fuel delivery and cut the rich 8 stroking as if it was being choked.
The mutes IMO only affected the overall breathing and exaggerated the effect of balance pipe breathing low RPM/throttle characteristic, and was not the actual source of the problem.
