my fiesta is missing whisht driving nd the fuel guage is reading alot less ?

i recently blew my head gasket and bent a com rod we put the car back together and now im having funny proplems with it.it seems to only start missing and that when its been driven for a period of time such as 10 mins.plus my fuel guage is reading alot lower than wats in there could my car be shorting out maybe?and where is the automatic choke bolted to on my car please someone help??