Make sure the sensor gap is correct 0.2mm to 0.3mm, often you might have to gently bend the basplate of the sensor so that it lines up square to the arm lobe, but never usually that bad.
Then when timing up, make sure the scribe mark on the dizzy body outer ring, exposed when cap removed is dead in the centre of the rotor arm alignment when sighted along it's path, easier to do than explain.
Make sure the connector is on the correct way in dizzy, but sure it wouldn't run if that was the case.
tabetha