This one is confusing me. changing the plug should not cause your issue. However you may have damaged the wire connection to the boot when you changed your plug. Try unscrewing the spark plug boot and then cut off about 1/4- 3/8 inch of the spark plug wire. screw the boot back on and see if that corrects the issue. Based on your description of the problem I would guess that your exhaust could be plugged, but the chances of that happening at the same time you change a plug is not likely. Hence my confusion.
Check the card intake boot for cracks. check the pulse line from the
Engine to the fuel pump. if the ends look chewed up I would trim them off and reseat the clamp. You can also check the return fuel by looking your fill neck of the gas tank while it is running.
Hopefully these are some things to check - Hopefully this will ID your problem.