I did a 13 kilometer ride today on the same route with incline at Thompson road, Chancery lane, Balmoral road and Goodwill road.
This time I tried to push the pace harder but I suddenly felt that the handlebar was shaking. A slight turn will wobble the entire front of the bike. I was a bit worried and had to stop to check what's wrong. I tightened the stem bar clamp. It did eliminate the shaking but the ride is still a bit shaky everytime I pushed it hard on incline. I'm still not sure if the stem bar is really the cause or if this is a known problem/issue on folding bikes. I'll try to ask around and do some research and will update this entry if I get any good findings.