Probably too lean. See what main jet is in there. If your old carb worked for a while (assuming you have it) take the main out of it and clean it and try it. This is a replacement right, or is it an aftermarket carb? Turn the mix screw all the way in till it seats, don't apply too much pressure, and then back it out about 2 turns. That should be a decent starting point. If you messed with idle speed, look through the carb and adjust that screw so there's a few mm opening. Whenever you start it, make sure it's on the stand and hold the brakes just in case it's revving too high. If it does rev to high, kill it and adjust the idle speed screw so there's less opening.
So you have tried the 70 or no? The 57 sounds way lean to me. Even if it were rich stock with the 70 main, it may not be with the 70cc. I've used anything from a stock 70 up to a 95 in stock carbs with 70cc kits.