backfires when i turn key off

TrailBeast said

What carb and manifold are you running"
A dual plane manifold could do that since left and right banks run on separate sides of the carb.

Click to expand...

its a 600 holley vac sec. with a edelbrock street master.
and it ran good when i had it running. i didnt do the timing when it was running though. but it would idle without me reving it up.