Fueling restriction

Within the last two refuelings of my 1989 sl56 the fuel pump nozzel kept tripping out. I had to set a filling rate very slow initially then gradually raise the rate to the point of reasonable. I have checked under the car and can not find a vent line. I have not found a charcol filter under the hood which in some cases is the culprit. So comments on my problem and how to resolve it.