I am brand new to biking. I purchased a used 1987 Trek 1500 as a beginner bike just to make sure I like biking. The bike has a mix of Shimano 600 and Shimano Sante components. It is a 7 speed drivetrain. I am having trouble with the front derailleur and wonder if it is bad and can be replaced with a new/different derailleur. First, the derailleur does not seem to be very responsive, especially when shifting from the small chain ring to the large. It takes several revolutions to shift properly. Second, the chain is often thrown to the outside of the large chain ring when shifting. Third, when on the small chain ring and the large cog, the chain rubs the inside of the derailleur.

I have tried adjusting the H limit to fix the chain throwing problem, but even with screw all the way in the chain is still thrown if I am not super careful. I have also tried adjusting the L limit to fix the chain rubbing issue, but even with the l screw all the way out it still rubs. Unfortunately, I am not fit enough to not need the small chain ring and large cog. Thus, I would like to get it fixed.

What options do I have? Can I buy a new derailleur? I don't want to put a ton of money into the bike as I would prefer to just buy a new bike. At the same time, I want to get the derailleur working properly so that I can ride it until I can afford a new bike and also, so that I can sell the bike as a working machine.

Thanks.