I replaced my downtube friction shifters (which were Shimano 600, and probably pretty nice) with Suntour barcons. (New old stock.) I much prefer the location on the handlebars, but the shifting on the chainrings has always required a pretty decent bit of muscle. (The cog shifter I can manipulate with finger pressure.) What's wrong here? Misadjusted shifter? Poor quality component? Or *gulp* am I just weak?