First make sure the flywheel zero marking is in line with the top piston. Meaning with #1 piston at TDC, the timing indicator should be at zero with the flywheel marking.
Four things need to be in the following state to synch:
1. Idle stop screw barely touching the block (i.e. backed off)
2. The cam's line should be in line with the eccentric screw slot (adjustment is made with by loosening the eccentric screw)
3. The carbs' throttle should be fully closed (adjustment is made with the tie rod from the timing tower to the carb's arms)
4. Timing indicator should be at zero.(adjustment is with the timing rod on top of the timing tower)
With the above the engine will not start because the throttles are fully closed. Hence, you need to set the idle speed by setting the idle stop screw, i.e. screwing it in until you attain approx 1000 rpm idle speed in neutral. When you set the idle screw, other settings from the above will also change, timing will advance, throttles will open and the cam's line will not be aligned with the eccentric screw slot anymore. This is all normal.
From here you can set the timing using a timing light.
