Without looking at it my first guess would be that your throttle linkage is rubbing/pushing on the end of your hand throttle wire. When you press the foot throttle it's slowly pushing the hand throttle wire too. I would watch the hand throttle wire as the throttle linkage is activated to see if that's where the problem is. If that turns out to be the problem the fix should be obvious. Good Luck.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.