Personally the biggest issue is how you reconnected the home button flex cable at the top by the group of flex cables. I've had SO many issues with the ID not working after installing a 3rd party screen, yet always worked the first time when installing the OEM screen. The quality of these flex cables that come with the screen just aren't good enough in my opinion. Not even close to good quality sadly. All you can do is keep disconnecting and reconnecting the flex until it works and do it with the battery disconnected each time. I ended up buying a used OEM screen off ebay and it cost me less than iFixit AND everything worked perfectly the first time of install.
No you cannot. The touch ID is unique and if changed will not work anymore no matter what. You must keeo your old sensor or else you'll never be able to use Touch ID on that device again.
Sound weird as in how? I'd just go over the basics and follow the C.F.S rule (Compression Fuel Spark) and make sure those are all in check. For some reason it sounds like the engine isn't getting fuel which you can test by putting a tea spoon of gasoline into the carb's mouth or by spraying engine starter fluid through it. If she fires up for a few seconds then good, you know she isn't getting fuel or maybe it's flooding. Check to see if you're fouling the spark plug when attempting to start it (it means you could be flooding the carb). Not familiar with your carburetor, but in some cases you'll need to re-adjust the float needle inside of it. If it isn't adjusted correctly you could be starving it of fuel or flooding it. Then, I'd start from scratch with the mixture needles though, especially after a clean. Close the LO and HI screws clockwise until they seat gently. Then back the LO out 1 1/2 turns counter clockwise and try to see if the bike will start so you can begin setting your idle. Once you're...
Did the back light driver go bad by any chance? Was the battery disconnected before the screen was removed and or when both were re-installed? If you do board-level repairs, it could be a filter problem, IC issue, resistor burnt out, coil damage etc.
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