Question about Yamaha YZ 125 Motorcycles
If you have a spark, but weak. It is possible that your flywheel is demagnetised. Then you'll need a spare.
If sparks are good, then the spark plug should be moisted with fuel after a few ( 10 ) choke kickstarts. If so you'll have a weak compression. Then you have to at least clean out the piston ring grooves ( dismount cilinderhead and cilinder ), or even change the piston rings or overbore the cilinder and place a new oversize piston kit.
If spark plug stays dry when kickstarting, the carburettor is faulty. Clean it out, check also the choke system. Check the air intake between carb and cilinder for air leaks.
Posted on Oct 04, 2009
Flywheel magnet may have lots of dirt or oil from a leak or somewhere insulating the pickup magnet which tells the cdi when and if to fire. So take off cover gently wiggle and remove wiring in rubber clean the magneto drum thouroughly and also the magnet, This usually fixes or improves spark intensity a new quality plug eg ngk bosch champion if you have to. Anew quality plug makes the difference.if you have not spark it is either the cdi not firing the coil or plug properly..Also a few good starting tips as above may offer assistance usually when magneto and pick up coil are clean and cdi ok you always get good blue strong spark.....as far as carby problems on 2 stroke chinese engines they clag float/needle and seat can stick/jam and will race and hunt up and down in revs due to airleaks at carby mounting area to barrel this makes carby tuning hard to get accurate without the bike idling low and stalling or racing. sometimes if you know you have good spark and it is a fuel problem giving the fuel bowl a couple of gentle taps with plenty of fuel in the tank can fill bowl to spec hight and if you start to see fuel coming from overflow lines you can smell if the carby after about 6 full throttle actuations on and off you know the carb is getting fuel and you should be able to start on choke easily, also sometimes after hard starting problems you need to idle the engine up it will start ans run ok then if it is revving to high turn counterclockwise 1/4 to 1/2 at most that should run start and idle well. If you are still struggling BRING IT TO BERGSTRUM  I'LL FIX IT FOR YOU CHINESE 4 AND 2 STROKE WIZARD ALSO HAVE SPECS AND WIRING SCHEMATICS..Hope i could assist you SCOTT...
Posted on Nov 16, 2011
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Posted on Jan 02, 2017
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