Question about Yamaha YZ 125 Motorcycles
Road bike test had put 330 main jet in it road it for about 15.min hard through the higher gears as we do flat track, and noticed it started to break down at the higher reving range then seem to cut in and out on the way home. then would not start at all then i changed plug no differance also checked plug for spark and there was no spark, i think maybe coil as it looks fairly old or maybe stater.
Posted by Anonymous on
Hi, Anonymous and the usual suspects are:
1. Fouled spark plugs.
2. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
3. 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.
4. Loose connection at ignition coil or plug between ignition sensor and module.
5. Spark plug cables in bad condition, shorting / leaking, spark plug cable connections loose.
6. Faulty ignition coil or electronic control module or CDI box.
7. Faulty CKP, CMP, or BAS sensor.
8. Faulty ignition switch.
9. Tilt sensor needs a reset.
10. Security alarm failing to disarm needs 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
How to fix No Spark Problem on Motorcycles and Dirt Bikes
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
Posted on Jul 18, 2016
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Posted on Jan 02, 2017
SOURCE: hard start, trouble idleing
Drain the carburetor. There should be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install new stock spark plugs. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.
Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. This process should get you back on the road.
Please rate this solution. Thanks!
Posted on Apr 02, 2009
SOURCE: bike only fires once
Okay, let's have a look at it. Say Ahaaa.
The probable cause of the problem is not the spark. Get a fresh set of Stock NGK spark plugs, ground the plus to the engine, and check each cylinder for spark as the starter button is pressed for 3 seconds or so. I will wager that the spark is present.
The likely problem is the fresh gas was put into a very rusty gas tank. Bits of rust now inhabit your carb and are having fun plugging up the carb. Look at the gas valve. With a little luck there is a small bowl behind the valve. Remove it and tell me what you see in the bowl.
Posted on Apr 11, 2009
SOURCE: yz 125cc 2003
Black spark plug means too rich , you will have to replace the spark plug since it has foul up and reset the air mixture screw on the carburator 2 and 1/2 turns outwards.
Check the air filter too.
Hope this helps.
Posted on May 23, 2009
If it wont do anything then it is likely that youve popped a fuse
But it sounds like the battery isnt being charged properly. Make sure the voltage across the batt terminals is at least 13.5v at tickover rising to no more than 15.5v at higher revs
Please mark this as helpful (if it has been!!)
Posted on Aug 14, 2009
Testimonial: "thanks, I will try what you reccommended"
SOURCE: engine turns over but wont start
could that be a possible fuel line crack? or the pet **** is fouled up. i got the same problem found 1/2 in crack in the fuel line. from trying to start it before i found the crack i dryed out the carbs. im a girl and its my first bike just learning
Posted on Oct 15, 2009
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