Car Backfiring After Re-fitting Injectors

[pugpete1108 62 1 Cars]

i went to have a look at the pulsar i was ment to be buying, its from a friend so he is honest.

he had the injectors out as the car never really ran properly (not as bad as it is now), when he came to put them back the car is really down on power and misfiring badly, also blowing black smoke out on acceleration.

 

would this just be a fueling issue (as i thought)?

 

or something else?

 

any help would be appreciated