Hi Al have a look at your springs in the slides they could have lost a bit of spring to them and could need a bit more stretch in them or replace with new or stronger springs I had this problem way back in the early 90s as the slides were a bit slow in dropping back down fully, also look at the O rings in your carb adjusters or anywhere air could be leaking into the carbs, are you running with chokes or none, back in the early days with my new Norton mine would idle a lot higher on hot days while out riding and stopping, I sorted this out by installing a Lochard oil cooler and never had a problem with high idle when hot ever since, does it do it now in our colder weather or is it only in our hot weather does it do it.
Carbs when pulled down could look good but needle and jets do wear out depends on how many miles you clock up, my Norton was a everyday rider most of its life till 2013 when I brought my new Triumph Thruxton but when riding all those years every day I would replace needle and jets ever 3 years without fail as from vibrations the jet wear oval and Amal rebuild kits are cheap for keeping great running.
does your Norton idle just right when cold but as soon as it warms up its sits too high could just need the idle screw to be adjusted out a bit more as the slide not dropping down enough when hot, your bike should not idle good when cold unless you using chokes, I would take a small screw driver with me and adjust the idle/slide when the motor is hot.
I have just gone back to running with my old Amals after a 12 year absent and when tuning the carbs up in the shed I had to readjust them while out and about to get things set right when the bike had done a few miles and stops, I be dropping your idle screws down a bit when it does it, put your hand over the end of your mufflers when stopped and feel which side is doing what, you be able to feel if one cylinder is running higher than the other if both side are doing it just lower your idle down, no use doing this till your motor is at running temp.
I run K&N air filter on mine so its easy for me to remove them and stick my fingers in the back to feel my slides and feel if both slide are dropping right down while on the bike or feel for tight spots.
If I had your Norton in my hands I am sure I would workout what the problem is but as we don't its hard to know but I am sure its only something simple causing it if the bike is running good other than the slides not fully retuning.
If the Norton is running good no need to replace the carbs, I have ran my Norton for years with worn out slides and it still ran good but didn't idle so well had to keep the throttle open a little but a new set of Amals way back in 1980 which I am still running and to my surprise the slides are still good even with a lot of miles on them.
Ashley
