Pymongo connection timeout from remote machine

I have a Bitnami MEAN Stack running on AWS EC2. I'm trying to connect from a remote machine using PyMongo.

from pymongo import MongoClient
conn = MongoClient('mongodb://username:password@ec2blah.us-east-1.compute.amazonaws.com:27017/dbname')

but I keep getting an error along the lines of pymongo.errors.ConnectionFailure: timed out

I have edited /opt/bitnami/mongodb/mongodb.conf to supposedly allow external connections by commenting out bind_ip = 127.0.0.1 and uncommented bind_ip = 0.0.0.0 and all permutations of commenting/uncommenting those lines.

I've looked over the web for about 90 minutes now trying different things but without luck!