Problem exist after timming belt was changed

1991 Toyota Camry V6
I recently had my timing belt changed. And now, my car won't accelerate right, after an instant stop, it takes a long time for me to accelerate up to 30mph. After that, it's normal. Then when I'm on the highway, sometime there's blacksmoke comming out of my muffler for about 5-7 secs and then it stops(the harder I press on my acceleration pedle, the more smokes comes out.) Can Someone please give me some sorta clue of what's going on?
Thank you!
Already check the timming, and it doesn't have nothing to do w/ it.