Just purchased a 1991 F150 302 2-wheel drive last week. it ran great for a few days after picking it up. i added in some "gaurenteed to pass" emision cleaner with a full tank of gas. on my way to drop off the truck for safety (driving on the highway) i noticed a hesitation while driving at idle speeds between 50mph-60mph that day. no hesitation under hard acceleration. hesitation went away that afternoon. then it started hesitating while sitting idle in the driveway. put my hand to the tail pipe while idleing. lots of fuel moisture and black smoke out the tail pipe. no check engine light on.
I have changed the following in the past 2 days:
air filter
plugs
wires
fuel filter
rotor and cap
PCV filter

none of the above has helped....actually made it worse.

any recomendations for troubleshooting

Thanks