Question about 2003 Yamaha YZ 250

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Yz 2501989 model had new magneto new coil new cdi but bike hard to start and backfires how do i get it to start smoothley

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  • Yamaha Master
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Hi, Mountainjoin for more information about your question and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Bike Backfire And Hard To Start
2000 YZ250 Back fire Yamaha 2 Stroke
YAMAHA YZ250 LC Owner Service Manual
OEM parts for Yamaha

Posted on Jul 26, 2016


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Posted on Jan 02, 2017

  • 149 Answers

SOURCE: my bike is backfiring what could be my problem

try richening up the fuel mixture, it could be that its running a bit lean... hope it helps

Posted on Aug 14, 2009

ollie reece
  • 1167 Answers

SOURCE: 98 YZ 250 started sputtering at higher rpms?

just change the plug buddy use a br8eg and get back to me if still not starting

Posted on Sep 28, 2009

  • 1508 Answers

SOURCE: 04 yz 450 backfires and is hard to start when is c...

Runs better with choke means the mixture is lean,
Has the exhaust been changed.?
Did this problem just begin.?
Check for air leaks on intake manifold.
Clean carb.
Check valve clearances
raise the needle jet one notch
one size up in the main jet.

check one item at a time, and write notes about jetting changes.and improvements
I also run Moreys upper cylnder lube, helps starting hot or cold, and helps stop "cough stopping" with heavy rear brake use

Posted on May 23, 2010

  • 42 Answers

SOURCE: backfire

Your plug may be firing in a fouled area. When I have a problem like this, I 1.change the plug. 2. Take the carb and have it cleaned in a sonic bath and my honda dealer(They are the only one with this cleaner in my area) for about $25. 3. Check to insure that the fuel mixture screw is set correctly(about 2.5 turns), and 4.clean the air filter or replace it.

Posted on Aug 28, 2010

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Did you line up the stator plate line with the notch on the cases? Sounds like your ignition timing is set a bit retarded. I would pull the side cover off and check the timing marks.

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My 2004 yfz 450 wont start i changed plug and stator still wont start you can hear lil backfire from pipe when trying to crank

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

Bike has no power but will still crash start bike will also only go if the lights are on when lights are off bike have poor idel and will not accelerate i was thinking maybe ignition coil

It is more likely to be either the Regulatoer/Rectifier or the Magneto coils or pick-up. Your magneto sends a series of pulses at various revs. This is changed and evened out by the Reg/Rec. First step is to check quality of all connections from magneto upwards to all relevent components. IE; ignition coil, CDI unit, Reg/Rec, battery (if applic.). If the bike normally runs with a city light or running light when ignition is on, then check all switches for crossed, pinched or broken wire connections, especially around headstem area. Ideally, a service manual with relevent ohm resistance figures and a multi-meter should lead you to the problem. CDI units, Reg/Rec, Magneto Coils and pulse coils are very expensive as are ignition coils. They will all be affected eventually if the problem is not identified and fixed. Goodluck.

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I need a cdi magneto or fly wheel rotor and can't find the right one

buddy is that the cdi unit the stator plate and the magneto ???

Oct 12, 2009 | 2004 Yamaha YZ 125

1 Answer

98 YZ 250 started sputtering at higher rpms?

just change the plug buddy use a br8eg and get back to me if still not starting

Sep 28, 2009 | 2004 Yamaha YZ 250 F

2 Answers

Yz125 no spark

G'day i am a . YZ 125 j ...lets see now! You could perform these tests yourself.Check your plug CAP,if in doubt replace it with a new one. Take the below ohm figures and see if they match up. Pulse coil: white/blue and white/red= 310 ohms. low speed coil: Green/white and Black/red= 900 ohms. high speed coil: Green/blue and black= 55 ohms. hope this has helped in some way to helping you solve your problem.If it has please leave feed back.Ride hard , see ya,Tabbycat

Jul 22, 2009 | 2003 Yamaha YZ 125

1 Answer


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.

Dec 14, 2008 | 2004 Yamaha YZ 450 F

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