Btw, I don't know if you said if you took the low speed screw out, and I don't know if it applies to your carb, but here's something to look for. On my Magnum carbs, the low speed needle is a long, thin rod that has to go in to a small hole when installed. It's possible to put it in out of alignment, so it misses the hole in the end of the spraybar. When you do this, it's like not having a low speed needle at all, and everything goes really rich and runs poorly. Usually you can see if this is the case by looking down the carb throat and making sure everything is lined up right.