They use the same fuel pump.
Does the problem now occur regardless of which tank you use? If so, then your problem lies from the carb to your fuel selector switch. Change your fuel filters, inline if you have it, as well as the one going into the carb.
Basically, with fuel related issues,, Start with known good and work from there. Especially if you have had it sitting for 3 years with gas in the tanks.
I would, replace the filters, drop the tanks, drain and inspect them and the pick up tubes, inspect the selector switch. put it all back together. test, if still trouble, check to be sure there is fuel flow at the carb verifying the mechanical pump is good. If still bad, take the carb apart and clean it.
I'm guessing that you had some gunk in the other tank which has now been sucked into the filters and or pump.
My past experiences in fuel issues tells me to take the time to make sure everything is in good shape. If there is gunk in the tanks, it may work for a while, then start up again with a totally different symptom, Then you start replacing ignition parts and chasing your tail. Take the time to drop and verify the tanks and pickups are in good shape. It will save you in the long run. ( especially if it has sat for 3 years with gas in there)
Brett