I am not afraid to break a nail, or have them painted.
Before you jump on that, my 4 year old grand daughter said "I am going to paint your nails papa." I couldn't say no, and I had to use an exacto knife to remove it the next day.
Now, back to the problem...I am a little confused at the bogging going down hill, as the throttle should be in a neutral position or somewhat closed going down hill, and a "bog" is generally associated with a loss of power when throttle is applied. Am I misunderstanding something here? Plenty of power going up hills?
Answering your questions- Yes, remove the (cool) plug and look at the center.
You can adjust the off idle to 3/4 throttle range by moving the C clip down for a richer mixture, up a notch for leaner. While we're at it, you aren't using 16:1 mixture are you? 24:1 for a gallon or so, then go to 32-40:1.