Hi My 87 Brat is having some trouble most of the time it runs great but at times it will start stumbling really bad. It will do that with out warning i can let off the gas and let it idle for a few seconds and it will be fine today it did it in a parking lot and I was able to open the hood it idled good but when I open the throttle it started stumbling . I notice a buzzing or humming sound that went with the stumble in the area of the carb that when it clear up the stumble was gone any idaes? Thanks Charlie

id start with each of your fuel filters, then start looking at fuel pump shorts.