White plugs means you are lean. Holley makes a lot of different carbs. Usually the mixture screws are located on the sides of the mereting block. I would buy a book on Holley carbs. You will gain a world of knowledge from it. Also the mixture screws only control fuel at and just above idle, then the run circuit comes into play. You say it's running fine at idle. As for the timeing, are you sure the advance is working? Does the timeing move when you increase the RPM? Again, check the accelerator pump. You need a good shot of fuel when you tip open the throttle because you loose all your vaccum which draws the fuel. Also double check your float level. Good luck.