Mercedes 76' R107 Does not run on all 8 Cylinders
 

I just recently inherited my great grandpas 1976 450 Sl. However, on low RPMs it only runs on 4 to 6 of it's cylinders, but as soon as it starts to get into higher RPMs all eight cylinders start to kick in.

I've replaced all the filters, fuel pump, and spark plugs. Any advice or pointers on what the problem might be are greatly appreciated, thank you.

distributor cap and rotor, plug wires and vacuum lines. run car in the dark to check for electrical shorts in the engine compartment.