Question about 2003 Yamaha YZ 125
Hi, David and the usual suspects are:
1. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
2. Failed alternator/generator and or voltage regulator.
3. Loose or corroded battery terminals and or cables especially the "NEGATIVE" cable, look for loose, corroded, or broken connectors inside the cable harness at "BOTH" ends.
4. Failed main circuit breaker or ignition switch, check for loose connections and continuity.
5. Failed system and or ignition relay, check for continuity.
6. Failed ignition coil, ignition/electronic module.
7. Failed CKP, CPS, CMP, MAP, TPS, or BAS sensor, corroded, loose or broken wire connector pins/sockets.
8. Throttle cables and or idle speed improperly adjusted hot idle speed should be 950 RPM to 1000 RPM.
9. Air/fuel mixture screw improperly adjusted.
10. Accelerator pump damaged or not working.
11. Water or dirt in the fuel system, carburetor or filter.
12. Restricted, blocked or kinked fuel line.
13. Fuel tank empty.
14. The gas cap is not venting properly or fuel tank venting system blocked.
15. A failed fuel pump, pressure regulator and or fuel injectors.
16. Vacuum line from intake manifold to petcock broken, cracked, or not attached, carburetor vent line plugged.
17. Needle and seat stuck closed in the float bowl.
For more information about your issue and valuable "FREE" downloads that you need please click on the links below. Good luck and have a nice day.
yz 125 wont start
98 YZ 125 won start
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
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Posted on Aug 01, 2016
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Posted on Jan 02, 2017
SOURCE: yamaha yz125 wont start...
hello there guys, listen a top tip is when the engine's cold tip the bike almost right on its side nearly touching the floof, wait for the petrol to poor out of the carb over flow pipe, this should take a matter of a few seconds, stand the bike back up again and kick and that baby should start right up, if it does then you have a problem with your float, if it still doesn,t then take it to a shop and get them to check it out, hope this helps. regards sam
Posted on Jan 24, 2009
There is a proper way to start the engine. Four controls are on your bike to assist in starting.
Top rating for this answer? Thanks!
Posted on Jun 11, 2009
i dont know what all you have tried so far, but check the fuel filter, usally in the tank above petcock. the compression seems fine as you had to bump start it in third gear. you can feel the compression of a bike when pushing it in gear, like a bike with bad compression you could push in first without wheel locking
Posted on Sep 10, 2009
Testimonial: " lots of gas , injector cleaner in the gas, spray cleaned up carb in frame,pulled of valve cover cam looks burnt blue in colour lack of oil? valves "
Compression is too low!
Replace the piston rings.
Also check continuity from engine to frame till high-tension coil...
Check if breaker points aren't dirty ( clean out with fine sandpaper )
Check breakerpoint settings
Posted on Nov 01, 2009
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