E30 Zone

i own an '86 318 m10 that is honestly my pride and joy. to get to the point directly, the car lurches during normal acceleration, particularly at the beginnig of a gear change, not so much in the higher revs. i've since changed the spark plugs and it worked fine for a while, but it started again, with the new plugs. at idle, its initially rough but soothes down as it warms up.
also, does anyone know about bmw carburetors being replaced with fiat carburetors? i'm told i bought the car with a fiat replacement and i'm looking to get a good replacement. anyone know how much that might cost? thanks all.

might just need the clean the injectors

An '86 M10 will probably have a carb. Try some Redex down its throat while revving it to clean out any deposits/varnish. Also put some in the fuel tank and take it for a blast down a motorway. I wouldn't recommend Fiat parts on a Beemer

Are the M10's not designed for leaded fuel? (and thus need lead-x or similar added to the fuel)

Could this issue not be caused by worn bits due to a lack of lead in it's pencil (I'm sorry, I couldn't resist )?