Gibbo1

Hi all, I'm new to the club and 911 ownership, my 1979sc was running fine, It has developed a strange fault, it starts on the turn of the key, ticks over at fast idle until warm then drops down to the correct speed, it hunts a little but not too bad, when you rev the car through the range there is no discernible missfire, but when driving slowly increasing the revs the car stutters just before 2000rpm and continues until approx 2700rpm, after that its fine, also if you accelerate hard its unoticable, and cruising in 5th at that rpm it is barley noticable, the fuel pump was making a hell of a din, so i've changed that and filter, I've also adjusted the valves(and oil change), and checked the timing(5 deg BTDC), the coil tests ok as do the leads( the HT lead coil to dizzy 980ohms?), the rotor and cap are relatively new. checked the plugs and they are all the same colour, black around the bottom of the thread and a little up the contact but the electrode and tip of the contact is a biscuit colour, do you think its running rich if so why does it only affect running at 2000rpm, any help/advice would be greatly appreciated...