On my engines I've had problems with swarf inside the black plastic part where the fuel line connects. This comes from when they drill the hole through it (I guess). You'll need to remove this swarf and also check how well the hole lines up with the grove in the brass part. On my engines this groove was too shallow and slightly miss-aligned with the hole in the plastic part. If you have a lathe you can easily increase the depth and width of the groove, otherwise I guess one can do it with a small file as well.
The low-end is way too rich as they didn't put any type of compensation on the low-end. You can add an airbleed hole though which will improve the throttling. Here is a short video of one of my engines;