Hi, Lissahere and the usual suspects are:
1. Fuel tank empty.
2. Fuel supply valve/petcock turned off.
3. Fouled spark plugs.
4. Engine flooded as a result of overuse of the enricher.
5. Vacuum hose to the fuel supply valve/petcock disconnected, broken, cracked, or pinched.
6. Fuel valve/petcock or filter clogged.
7. Fuel line to carburetor or throttle body pinched or kinked.
8. Carburetor float stuck.
9. Fuel injectors clogged.
10. Severely discharged or damaged battery, you need 12.5 volts or better and be able to pass a load test if necessary.
11. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
12. Loose or corroded wire connection at the coil, battery or plug between ignition sensor and module.
Spark plug cables in bad condition and shorting, cable connections loose, or connected to the wrong cylinders.
13. Ignition timing incorrect due to a faulty ignition coil, ignition module or sensors (MAP, CMP, CKP, O2, TPS, ETP, IAC,or BAS).
14. Faulty neutral, clutch lever, or kickstand safety switch.
15. Faulty fuel pump or fuse or relay.
16. Faulty CDI box if applicable.
17. Tilt sensor needs a reset.
18. Security system not disarming alarm needs a reset.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Dirt Rider Magazine
yz 125 wont start
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/gregg_c0ec1df182c7330e