It sounds like the the carb needs some tweaking. I have had to adjust the metering lever on one of mine to keep it from running with the burble in the mid range. What i do is change the pop off pressure to between 12 and 15 pounds and if it still wants to burble then i will adjust the lever height so the arm is above the surrounding casing put the diaphragm cover back on and see how it will adjust and runs then do it again until the burble is gone and transition is good.