If you say spark is weak, that's what you want to diagnose first. Do the rotor, leads, plugs (do NOT use platinum plugs) if you haven't already, then perhaps check coil, trigger box etc

later

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg