MG Car Repair: bad fuel, stale gas, gas tank

Question
My sister has a 1979 MGB that she has restored. She became ill and hasn't drive it at all in the past year and a half.
When she stored it she said she filled the gas tank and put some kind of additive to the tank before she put it away. Just recently she took it out to get it in running condition, suach as a tune-up oil change. She said it ran good the first few miles and then it started to sputter and backfired a couple of times. She would like to know if she should empty the gas tank or is there something she can add to to the gas to clear this up?
Please be advised that I know absolutly nothing about cars,so I'm little help to her!
                                  Thank You


Answer
Hi Bill,
Even though she put an additive in the gas, a year and a half is too old for gas and it should be drained and fresh gas installed weather or not that is the cause of the sputter. You will have a hard time diagnosising an engine running problem with stale gas in it.
Drain the gas then see if it needs further work.
Howard