Replace the condenser and clean the points with some 320 wet or dry. Check the point gap its .020" for a distributor and .013" for a mag.
If you have a distributor make sure battery voltage is getting to your coil. With the points open you should have voltage on both terminals.
Make sure you're getting gas to your carburetor.
Pull off the gas line at the carb and see if there's a full stream of gas from the tank. If there's full stream of gas remove that tube fitting where your gas line connects and look for a screen that may be plugged. As Old suggested you need to post more info. Your coil could be failing when it warms up. Pull off a plug wire and using a helper see if there's fire to your plugs when the engine quits. Hal