I take it you have the correct coil for dizzy e.g. MEC or HEC? Does your dizzy have a centrifugal advance governor or does it rely on an ignition controller?
When you say backfire are you talking about the exhaust or the carby? Exhaust popping is generally caused by a lean mixture (vacuum leaks, gasket leaks, over throttled idle cct or dirty jets). Backfire is generally caused by igniting fuel in the intake ports or runners, caused by bad valve timing or overheated exhaust valve or premature spark.
So to your problem, well I don't know because I'm not there, but have you taken into account the increased energy of the coil: your ignition kernal will be much larger than with points because of the higher voltage tension and you may need to increase the plug gaps. Your plugs may now be too hot and still glowing when the fuel starts entering.
You may also be inducing a voltage into an adjacent lead that just happens to fire while it's cylinder is filling= cross firing. Magnecor 8.5s or larger wire wounds are your friend.
What's your dwell when it starts carrying on?
Is the ignitor/amplifier the correct one for the number of cylinders?
Hows your acceleration pump plunger behaving?
Does the cap have any soot marks inside from arc burn?
Your primary current will almost double, is your wiring up to the task or is there excessive volt drop?
And in keeping with the most obvious being the problem, are your leads in good clean condition? Is the continuity ok when you give them a good wriggle? Are the porcelains on the plugs crazed or cracked?
"She gave me a look only a mother could give a child."
Last edited by Wally : 12-15-2005 at 08:31 AM.