I find them just too slow for me and I agree with the underpowered assessment. I wouldn't alter the bobbin case or retime to take 15x1 needles, that's just my opinion. I've owned several and have sold a few. Yet, I just can't part with my black 319. I really should, though as I don't use it. I prefer so many other machines over it. Not one of Singer's best, for sure, but it is an interesting machine that I just can't seem to let go of.