Hello I've been upgrading Shimano Revoshift to Tourney Thumbshift (SL-TX50) on my son's bike (Python Rock). Rear derailleur was really easy and no problem (and much improved shifting!) but front one is causing me a headache … The main issue I have is that the shifter "maxes out" half way round and is really tight. If you imagine the shifter moving from "twenty to" to "twenty past" (which it does when it's not connected) I'd expect the small / middle / large chainrings to be engaged at "twenty to", "o'clock" and "twenty past" respectively. However they engage at "twenty to", "ten to" and "o'clock", and the shifting is really stiff. This suggests to me that the derailleur is trying to move too much for the shifting provided. I have the H screw all the way out so surely it can't be to do with limits (or the shift from low to middle would happen at the right place on the shifter)?? The derailleur is a Shimano FD-TZ31, which the vendor of the shifters has advised is suitable, so I'm a bit stuck! I suppose he could be wrong and I could try replacing the derailleur but want to make sure nothing else is going on first (like me being stupid!) Any advice much appreciated! Thanks, Paul.