knocking on acceleration

I have a 1985 Chevy S-10 with a 2.8 L V-6. The truck has been running rough lately and so I checked it out last week. What I found was a big whole in my vaccuum line leading to my deacceleration valve. I replaced theline, the PCV valve, and then shot some B-12 into the carb to clean it out. Now when I accelerate the engine has a terrible knocking sound. The sound doesn't seem to be noticeable at idle, but only when I accelerate. The knock is very loud and seems to come from the carburator. When I accelerate quickly in recession there is some type of gas that is blown back through the carburator. I hope someone out there can help.

Brandon

Check the timing.

The carbs are pretty good, so I wouldn't expect it to have much wrong.