Will not throttle down between gear changes!

Could an opinion givin as to why my engine will not throttle down between gear shifts, and seems to not idle down quickly when coming to a stop in 1st gear.

I'd say two things could cause this:

1.Vacuum leak.

2.Stuck mechanical ignition advancer.

To find the vacuum leak, warn up the engine, then spray brake cleaner around the rubber carb boots(ducting)and the carb holders between the engine and carbs.The rubber plugs on the vacuum sync. fittings also need replacing too as they crack with heat/age

If the idle goes up, you've found the leak.

The ignition advancer is located behind a CD sized cover on the right side of the engine(as you sit on the seat).

Remove the cover with the engine off and give it a twist by hand, if it does not return to it's original position, cafefully note how it's installed, remove it and clean/lubricate it.

Light sewing machine oil or 3-in-one oil is what I have sued on my bike advancer for years.

I will try both and let you know. Thanks Don

id guess a vacuam issue