Just recently got into a 240z '72. 280 motor installed, but original '72 3 screw round top SUs. Drove it for a bit to find that it was well tuned to be at high idle. I believe this is to have the ol' girl stay running. I then had to ring a friend to grab me, as I was on the side of the road!! All this to say that, I rebuilt the SUs brought them back to spec and reinstalled( cleanest part in the engine bay ) got her running at high idle, but have a loud slapping noise coming from the front SU! was thinking that it might the mixture but no matter what I do it still there!! any suggestions

 

Did you put 3cc of 10w-30 oil in the screw caps of the domes?

 

Yes sir 20w really

 

thinking now that it might just be the needles at the base of the pots

 

Sounds like an intake valve not closing all the way. Check valve lash and if it's good do a compression check, could be a bent intake valve.