Reviewing papers after leaving research for teaching? I had been an active researcher until two years ago and published several papers and reviewed several papers as expected. Two years ago I took a teaching position. I teach 3 classes/semester but most classes meet 4 or 5 times a week, so it actually feels like 4 classes. I also do extensive work with undergraduates. I do some research, but it is very minimal (corresponding to the high teaching load).

Due to my previous research past I am constantly getting requests to review papers (3/month). Due to my change in work duties, I have to decline many of them (but I do review some papers).

My question is:
Should I explain that I am declining due to my change in work duties? What about if it is the same editor or journal that keeps sending me papers to review? How do I best/ethically proceed without hurting my chances to publish the few papers I plan to submit?

Additional information to clarify: I am not too worried about my chances to publish (my current position requires very minimal research). I am mostly worried that I will get known as a bad professional. By the way, my current institution is officially a top tier research university (and they advertise themselves as such), but my department is not (we barely have a masters program). It is very easy for colleagues to think that I am active in research unless I explicitly tell them about my current duties. It gets even more confusing since some papers take a long time to get published (after acceptance).
There are (at least) three issues here:


Your time. If you're unable to spend time due to teaching, than that's a perfectly acceptable reason to decline.
Your duty. If you're no longer publishing research, then arguably you're no longer obliged to provide the service of review to those who do. So, don't feel obliged, but you may still enjoy this.
Your expertise may no longer be up to scratch. In particular, you may lack access to some relevant publications and/or may no longer follow recent research to be on top of the field. In this case, you cannot provide an adequate review (w/o an unreasonable effort) and should decline.


In any case, you don't have to feel apologetic when declining a review request, though it does not harm to briefly state a reason.