Sounds like your timing is good enough to start but not ‘right’. With the engine running, possibly with the throttle held open a little (jamming a bit of card under the throttle linkage or having the choke open a tiny bit will work if you haven’t got a helper) if it won’t hold idle, turn the distributor again till the revs stop increasing, turn it back a fraction. If the engine will run without the throttle now then close the throttle. Repeat the process with the throttle at idle, tighten the clamp bolt and road test.