i've owned hundreds of tomos peds and never had this problem. at least not that i can remember.
is the fitting on the carb that covers the little filter moving by any chance?
when you install the fuel line are you making it long enough that it doesn't have to make any sharp bends?
a straight shot is usually your best bet, but on these step through models i find that it is better to rought the fuel line so that it is in the most relaxed position possible and does not have to make any tight turns. and on the 94 models with the short intake, they can be a bit more of a challenge to do this. try loosening that fitting on the carb then run the fuel line so that there is no way it will crimp over time.
or get steel braided fuel line from your auto parts store lol.