440/AFB backfire

I have twin 440s in my boat with AFBs. I pulled one of the carbs because of a fuel leak. Turns out, floats were set too high. Guy who fixed it, solved the problem, but also moved my mixture screws from where I had them. Now, when I cold start, I am getting backfiring until she catches and then runs.

I thought I followed directions on setting the mixure screws by listening for RPM changes, but apparently I'm way off base. I will ask the guy again, but I would welcome second opinions as I watch Sunday football.

Timing was on prior to pulling carb.

How do I solve the backfiring? It did not do this prior.

Thanks

Backfire means it's lean, turn the screws out.

Also, see if the linkage to operate the accelerator pump is set to the MAXIMUM. Your buddy may have re-set it to maximum economy, as for a street application. You want the pump to move the most it can, via the linkage, as the throttle is opened.

Jeff