running really rich will do that. it will feel like it stumbles and accelerates really slowly. the cars adding a lot of fuel and pulling timing, making it way worse.
when mine went bad it was right after a rebuild and really sucked because i had high hopes for the "new" power. When i replaced it, night and day difference. i took it out for a test drive and it had just rained a few hours before, so it was still a little wet. i was surprised to say the least. went easy on it in first, easy into second, mid second started to get on it and just lit up the tires, ok, sweet. put it in third, just more spinning:naughty: my car had never done that before.
get that fixed!! youll be happy you did.
but make sure your wiring isn't bad too, thats also known to go bad.
good luck!