Now that you have the throttle working properly, consider installing lighter throttle return springs on the carbs. These are the external springs visible on the engine side of the carb's body.

The stock springs are stiff, meaning you will be fighting them on long trips (the throttle 'lock' screw can help, but is a sub-optimal solution, IMO). The results is stiff neck muscles.

I installed a pair of EZ Pull springs on my 1975 R90/6 years ago and have never looked back.

Left Bing carb #: 64/32/11; right 64/32/12.

You want the Type 908 for your machine.

Needle nose pliers can help with the job.