Holley backfiring after cleaning - please help!

Hi all,

I have a 350 SBC with a Holley 600. The motor is in a car that has been
stored for 12 years, and the previous owner had turned it over
regularly using 2 stroke gas. The car ran really rough and it was
suggested that I remove the front of the carb and clean the primary
jets etc. I did this, and removed as much of the old gasket as I could
and replaed with new. Now when I try to start the car, it won't,
backfiring badly. What have I done wrong, or where should I be looking?
I don't think the float level was touched, but it may have been knocked
during ceaning - would this cause it? I have a rebuild kit on order,
but it may be a few weeks away (I am in New Zealand), but have a gasket
set bought locally. Any thoughts?

Kind regards,

Andrew