How much air does your 1980 engine leak? I've had success drilling jets but I went in baby steps. I drilled holes in my airbox, and now I have a noisy intake, it wasn't the answer. You need to have everything working right stock before you start trying to tune it. Get a new jet in the stock size and get it running right. Chances are if you were trying to revive a derelict bike you didn't get the main jet clean enough in the first place. You may find that the new jet will put things right. Also, tape over any airbox holes you may have drilled. Have you de-restricted the exhaust yet? there is a good tutorial on that. There are also other restrictions hidden throughout the intake system. Mine had a plastic insert in the intake and a restrictor tube in the air box.