If it passes the vacuum test, I would then look for trash in the main metering jet. If it is trash in the main jet, quite often you can rev the engine up and then put your hand on top of the carb. Sometimes this will suck the trash on through. I have also removed the top of the carb and sucked the trash out with an eyedropper. If all of this fails to fix it and you are sure you don't have a vacuum leak, you probably need to get the carb rebuilt.
