If you've verified that you have good fuel flow to the carb then it could be jets that are still stopped up and choke would be the only way to keep it running or the carb needle valve may be sticking in the seat not allowing enough fuel to get into the carb to begin with.Therefore the choke would keep it running in that instance also.Still good carb kits out there for these old machines that may solve the problem. Here's one for a 81-82 atc 200 for example.https://www.ebay.com/itm/Shindy-Carb...haaLnQ&vxp=mtr If that's not the year model you have,here's the list of kit numbers.Shindy Products, Inc. - ATV Replacement Parts Plus not a bad idea to check valve clearance. Should be at least a minimum of .003 or so clearance for the intake and exhaust valve,plus a compression test would tell you the condition of the top end.

 

My carb was the same way. I soaked it in my soaker can(available at most auto parts store, looks like a gallon can of paint) for 4 hours, then blew all ports clear with a can of carb cleaner. Reassembled, set the adjuster screws to initial start up settings and she fired right up. Took a bit of tuning to get the idle down where it belongs and then tuning the idle mixture so it doesn't load up by running rich, or run hot form running lean. Mike