make sure the float isn't stuck and or the jets aren't clogged it could be either getting to much fuel or most likely not enough. also make sure the lines aren't clogged, crimped crushed or anything else either that or its a stuck butterfly.
I addressed another carb issue before with you and unless it needs a good cleaning...it pertains to this also. The reason you can only run with the choke on is because it is running lean....closing the choke causes the motor to run rich. So here is the cut and paste from before.
Here's the lowdown on setting just about any Tecumseh carb. There are two needles, one on the side (that's the low speed needle) and one on the bottom (that's the high speed needle) Turn both in just til they stop....don't wrench them in any further or you'll mess up the tips. Now back them both out 1 1/4 turns. This is a good spot for starting the engine. Now start the engine and let it get up to operating temperature and put it to full throttle. Turn the high speed needle in till the engine starts to run rough or sputter (remember this location) now turn it out til the motor starts to run rough or sputter (remember this location) now go inbetween these two points and you should have your ideal operation range. You may have to lean or richen it a bit from here to fine tune it to your motor.
yes tempermental little crapers. had one 3.75hp murray pusher, didn't last a year and it was brand new when i got it. i threw it away when the darn thing kept taking my money. i saved the deck a put a briggs 3.5hp on it from the junkyard ran good and still does.