my friend who has a 305 in his 81 chevy p/u jacked up etc has a big issue he bought it from someguy and ever since he got it fired back up it makes a very loud KAPOW <like someone smacking a sledge hammer against wood> but the motor doesnt run rough. but that kapowing im scratching my head. ignigion is ok plugs are good wires arent crossed he just put headers on it no the kapow is just louder so whaddya think?????????...........hey tech your being paged ...............................scooter