I don"t know the specifics of your carb but requireing the choke to help under load usually indicates a lean mixture. Make sure it is really clean.Carb cleaner may help you really get a cleaner carb. Put a small wire through the passsages and blow them out with compresed air making sure they are clear. Make sure your main jet is clear and adjusted properly. Look at the needle and make sure it is not damaged. Make sure the float level is correct and you have unrestricted fuel flow to the carb.
Alort of problems arw erroneously ascribed to the carb when the ignition system is not performing properly. Make sure you have a FAT, BLUISH-WHITE SPARK, the color of lightning. Make sure the advance is working correctly and the ignition is properly timed.