Did you check both diaphragms? If you checked the screen, I assume you checked the one under the cover retained by the single large screw. Did you check the one under the cover plate retained by (4) screws? Under that diaphragm is the metering needle that often times sticks after long periods of storage. You can cycle the metering needle fork a few times and that should free that needle up. If the diaphragms are in good condition, you should be good to go as far as the carb goes.