I recently added the GM HEI Conversion to my truck and now it backfires when under a load. In addition it is running very rich. Should the timing have been adjusted after doing this? I have not been able to find any info on the settings with the HEI conversion. I probably should also look at adjusting the carb but I don't know which to do first. Any help would be appreciated.

You might have your distributor wires backwards on the HEI module. I know when I did mine I had them reversed the first time.

Timing and carb setting should remain what they were before the swap. The only thing HEI does is provide a longer dwell period and a hotter spark. That's it.

I second the suggestion that you try switching the pickup wires going to the HEI unit.

Thanks for the responses, I'll check that out this weekend.

Thank you again for the suggestions on fixing this problem. I just got back to working on the truck and I found by back-tracking through everything the the back-firing was being caused by the #5 and #6 spark plug wires being in the wrong locations on the distributor.

Way to go, glad you figured it out!!

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1964 Dodge Dart 270 four door. Three speed automatic 225 Slant with a Carter BBS carb.

You can't beat simple; no tools were abused in that repair.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC