A few different things can cutoff the circulation in your hands making them go numb:
The first is by supporting too much of your body weight on your arms during riding. This puts pressure on your hands and, especially when your wrists are bent (dorsiflexed) the added pressure will restrict blood flow.
There are a couple of ways to mitigate this: The easiest fix (but most expensive) is to get bar risers that make you sit up straighter so you will not have as much of your torso weight leaning on the bars. Everyone's anatomical dimensions are different, so what height is the right height for you is mostly a matter of trying different positions.
Another change you can make is to have your wrists cocked less while riding. If you start out by grabbing the bars with your wrist in a neutral (straight) position, the left wrist will be fine, but as you open the throttle your right wrist will dorsiflex. Try re-gripping the right bar so that your wrist is a straight as possible while actually riding down the road.
The most effective change of all will be to use your (much stronger) legs and abdominal muscles to support your upper body weight instead of your arms. You'll want to learn to position the balls of your feet on the footpegs (not the arches) and use your legs and feet pushing on the pegs to hold your torso up, instead of pushing against the bars with your arms. This is a tough change to make for most riders who have already become used to pushing up and back with their arms.
The other major contributor to hand numbness is from gripping the handlebars too tightly. You really do not need to grip the bars all that much during normal cruising. You can just rest your hands on the handlebars, with your fingers naturally draped and curved around the grips, with no "gripping force" exerted at all and still have perfectly safe control of the bike. You control the steering by pushing on one side or the other, not by pulling on the bars, so you do not really need to grip the bars for steering.
The stock position of the throttle spring creates too much closing force, which does require you to grip the right hand to keep it open, so you'll want to release the throttle spring one turn to make the spring rate softer. Just the weight of your hand should be able to maintain the throttle open after the spring unwind.
Many folks use a clamp on throttle lever (wrist rest, cramp buster, etc.) which can reduce the need to grip the throttle side even further. Once you get used to them being there, and using them, they become very comfortable. But many people have problems getting used to the flap being there and end up bumping it or catching it with a sleeve or something at an inopportune moment. I've used one so long now I never even think twice about it being there anymore. But it does take some getting used to.
Hope that helps
