Heffkid - Welcome to Ribnet!
I would maybe rearrange guernsey's thoughts:
Idle jet. What you describe sounds like it's set too lean. I don't have a manual for that machine, but someone will no doubt come along & tell you how many turns of the idle screw to start with, then its a caser of try it & see, turning the screw no more than about 1/8th turn at a time.
Air leak. If you can get it running on half cholke or by some other way, spray WD40 at all the gjoijts on the intake side. if it revvs you got a leak. While we're on the subject, you did use new gaskets when reassembling?
Needle valve - would be sticking to cause that, but you say you've cleaned it. Unless theengine has done millions of hours & it;s worn, but I still ereckon you are running lean.
Simialr thoughts on the float sinking - it would flood the engine as the fuel pump merrilyt filled the carbs. Also I guress you might have spotted it was full of fuel when disasembling.
Hopefully someone will be along soon with more detialed knowledge of that engine. If however you know which one the idle mix screw is, probably worth richening it up a bit.