Question about 2004 Yamaha YZ 450 F

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I have just installed a new uprated stator coil on my yz 450 2004 to run lights on my bike as well as the spark plug. However it wont start now at all? I have spark and when i kick her over i do get smoke from the exhaust? every now and again she will back fire like a rifle shot going off. Ive checked all the connections and emptied the carb bowl and flushed the carb through. i keep getting a spark but does the spark need to be a certain strength? It seems normal and strong, and ive also put in a new spark plug? someone please help? Is it the timing or is there some kind of internal shut off for lack of oil or coolant, i just dont know,

regards chris penny

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  • Anonymous Jan 31, 2009

    i HAVE a yamaha yz450 quad that will not start I cheanged the plug and set the gap just keeps turning over not even a cough from it



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Hi and welcome to FixYa,

Offhand, the backfire is significant. It indicates that fuel is getting inside the combustion chamber and it further confirms that there is spark. Being the case, it would appear that this is now a timing issue. A couple of ideas to explore:

  • compare the original stator coil and the uprated one; are the coil location on the same side, on the same angle, on the same distance from the edge;
  • there would be a guide notch on the base plate of the coils, are they identical and does it fit exactly back into position;
  • there would be a guide/lock pin that keeps the magneto/flywheel in position;
  • there would be timing marks on the magnet/flywheel that must coincide with marks on the engine case.
Good luck and Thank you for using FixYa. Happy Holidays.

Posted on Dec 15, 2008


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Yfz 450 only runs when pull started. Wasn't and haven't had any such issues starting it any time before.

Hi, Sal 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.
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My yz 250 will start with a roll start,but I can't

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Did you tried replacing the CDi for your bike?
Tell me what happen when you replace or borrow a CDi from your friend, just to check if it is the real culprit......

Sep 30, 2011 | 2004 Yamaha YZ 450 F

1 Answer

My yz 250f just died on me in the air an will not start I can push the kick start down with my hand seems like the top end is blown I'm not sure any ideas

Sorry to hear your bike stopped - There are way to many possibilities for this but the best advice i can give would be two things, (1) get a leak down test done (at shop if you don't have tools to do this) It will give accurate answers to if compression is low or valves are leaking etc (2) Check to see if you have spark to spark plug by kick starting bike with the spark plug connected and laying on the head of motor ( should be a nice clean blue spark)
if you have no spark then almost guarantied you need a new stator installed but this can be easily tested with a multimeter to confirm before you buy new stator let me know if you want more detail on tests etc
good luck mate regards Jamie

Aug 13, 2011 | 2005 Yamaha yZ 250 F

1 Answer

My Yamaha YZ 450 F runs but then stops?

The last time I came accross this issue was o3 YZ 450 it would start first kick then once operating temp died never to be started again until the next day or two
if this sounds like your YZ then most likely issue is the stator - it is very easy to replace it but you do need some special tools like t30 allen key and fly wheel puller to suit your bike
Happy to elaborate on installation if you want to tackle it yourself
regards Jamie

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1 Answer

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If the spark plug is not getting a spark then you will need to replace the starting coil! the bike wikk start then !...Is the engine getting fule?

Dec 17, 2008 | 2001 Yamaha YZ 426 F

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