That's where my $$ would be. Even not tuned, it should have gotten closer than 2 seconds.
If you went 2" smaller tires, you should have seen a jump too. With no cahnges to 60', it could be weather related, or track prep, or tire pressures, or....
Was your finish line rpm the same or higher? What did you play with tire pressure at all? You should have a lot to start with..like 18psi. Drop it if it spins at all by 2psi, until it hooks. You want the most pressure that will let it stick.
On the carb, a larger shooter will end the squirt faster. My suggestion would be to tighten the door a hair first, and try that. If there is no improvement, try to find a smaller squirtor than what's in there, and try that. If it gets better, then go back and quicken the air door a hair. You may also try adding a few degrees timing with the slicks...