General Discussion Forum

i have a 2002 cr125 and it runs great when is hot. but every time i start it after a week of not riding it will foul the spark plug.
i think is the choke. any other ideas or solution would save me alot of money.
it starts and foul the plug right away after that i change the plug it start and run good all day long.plug is br9eg oil is gn2 honda. mix 32/1.  

or anybody else who knows about it.  

Here read this thread Spark Plugs, The misunderstood component  
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leonel125:
i have a 2002 cr125 and it runs great when is hot. but every time i start it after a week of not riding it will foul the spark plug.
i think is the choke. any other ideas or solution would save me alot of money.
it starts and foul the plug right away after that i change the plug it start and run good all day long.plug is br9eg oil is gn2 honda. mix 32/1.

What you describe is a cold foul; which would indicate one of two things.
1.  The plug is not getting hot enough (what type of riding do you do? )  You can drop one step hotter on the plug (a BR8EG) and try it.
2.  Bike might be jetted rich (might just need a smaller pilot jet... again depends on riding you do)

Being a 2002, what shape is the top-end, reeds etc in?  If its original and has a large number of hours; it may be getting worn which can cause some fouling issues.

125 MX bikes are designed to run at high RPM most of the time, so they come with a cooler plug.  If you trail ride or don't keep them wound up; the plug can run cooler than it needs to to self clean and gets carbon buildup.  After its sat and you go to start it; it builds up more deposits and fouls before it can get hot enough to clean out (hence the term "cold foul".)

If you feel the top-end is in good condition, and the jetting is good; then try a BR8EG and see how it does.  After a couple rides, pull it and have a look at the insulator.

Let is know how it goes.  
Dave H 2006 YZ250
(2008 YZ 125 son)

Can't say it better then DJ just did.  

thanks for the explanation. i allways ride fast thats why i have never foul a plug,  my only problen is when i want to start the bike and the bike is realy cold exemple: a week without riding,it will foul the plug in less than 5 or 10 seconds even if i acelerate.when i take it out is wet n black.
do you thin cleaning it before triying to start will help? or trying to start it cold without the choke? thank you in advanced.  

Sounds like you want to check your idle jet. Make shure your air screw is at stock setting. And use a new plug with the choke on, And don't touch the throttle at all. And see if it will warm up like that. Do not give it gas untill it starts to bog alittle. After about a min you should get good throttle respounce. Also check the ARC for what kind of spark your getting to rule out the coil ect...... Let us know. YZ WOODS.  

If your plug is looking likew this.Then We just need to lean out the idle jet alittle assuming you have good spark and freash mix ect...I would not chang the heat range of the plug for just a idle start issue as that better for mid to top end.  

yes my plug is looking like that, is the idle jet the same as the slow jet as the manual said? i was reading what you wrote and you said no to touch the throle i'm been doing the oposite i allways try to acelerate as soon as i put the choke down to see if i can burn the oil.thats how i see people doing it.one more question woul a iridium spar  plug help? br9eix ngk. i going to ride on sunday i let you know! thanks.  

does the choke on make me run richer or leaner? i allways turn it down realy fast.  

Where to start....Yes the SLOW jet is the same as what i call idle jet.
Next. New plug. (NEW) plug. And with the choke ON. Give it NO gas..! Not even before you kick it! Then kick it hard and smooth! And fast!
Putting the choke down before the bike is not hot enough will just cold foul the plug as you did not warm the engine properly.
Put in a NEW plug. Pull the choke up.
DONT TOUCH THE THROTTLE! Kick it .
Then let warm up! Just try That! If that does not work, Then ill tell you the # jet.  

Also i did not hear you say that you have FRESH mix, A good spark, And ARC.  

yes my gas is fresh i use a new spark every week. i'm going to try on sunday the way you are telling me but i would like to understand the science of the choke.the manual said to pull it down a soon as the engine is on which what i has been doing.(obviosly not workin) u are telling me to leave on for a little while thats what i'm going to do.(without touchin the throle)
question #1 the choke on would make my bike leaner or richer?if richer, how would this help?if leaner,sounds good!!
question #2 would a iridium plug make any diferent?  

so far...sense if ridden 2 strokes....i think iv burnt up.....11 plugs in the last 2 years....thats before i switched to 40:1...sense then....its only been about 3 i think  

thanks twist for the awesome pic