First question you've seen me ask for backfire on decel, lol.
Do you have an exhaust leak ?
If so, repair it
If in doubt, have someone plug the exhaust holding shop-cloths
over the ends, and listen, be quick, as the shop cloth will get hot very quickly.
Good luck.
If it’s surging during cruise it’s lean. Light load cruise will be on the transfer slots and idle circuit so richening up the jets and rods will make only a very marginal difference.
“ported vac is 13” in park 10” in gear”
Please explain this ^^. Ported vacuum should be zero at idle. That sounds more like manifold vacuum. And if you have your vacuum advance on manifold vac you need to tune it differently. It could be surging at cruise because you have way too much cruise timing.
MY BAD.....Manifold vac for the reading, sorry I'll go back and edit.
Hooked to ported for va.
The surging happens at cruise at different speeds, so far the backfiring is at hwy speeds.
Same/similar issues prev to rod change, but "stalled" 3 times fairly quick.
Oh also using Edelbrock spacer.
Thanks all.