YZ 125 Fouling Plugs

My YZ 125 has fouled a couple plugs and I was wondering how I can stop it?  I JUST did a new top end and it can't have more than 2 hours on it and it is fouling plugs.  When I was breaking it in it fouled a plug but I figured it was the rich gas I was using to break it in (20:1).  I replaced it and continued riding.  Once I was done breaking it in I drained the 20:1 gas and put in my 32:1 gas.  I have taken a few rides with it and it seemed fine.  Today when I was warming it up I could feel it bogging out and when I started moving I only made it 200 ft before it was completely fouled.  Like I said I just put in a new top end in it and got it re-sleeved.  Also, I just cleaned the air filter if that has anything to do with it.  Please help because I want to go riding before it gets to cold.  Thanks in advance.  
03 YZ 125

Are you putting around to much?  
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I love this dirt stuff.

Yeah there's a couple of things that could affect it:

1: Like pop said, if youre putting around and not riding "on the pipe" it will foul plugs.

2: Jetting is too rich  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

Have you turned the airscrew any?  
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Stand in the place where you are, think about direction and wonder why you haven't
North Carolina

try a ngk br8eg. it shouldnt foul even if youre putting around.  

sscot600:
My YZ 125 has fouled a couple plugs and I was wondering how I can stop it?  I JUST did a new top end and it can't have more than 2 hours on it and it is fouling plugs.  When I was breaking it in it fouled a plug but I figured it was the rich gas I was using to break it in (20:1).  I replaced it and continued riding.  Once I was done breaking it in I drained the 20:1 gas and put in my 32:1 gas.  I have taken a few rides with it and it seemed fine.  Today when I was warming it up I could feel it bogging out and when I started moving I only made it 200 ft before it was completely fouled.  Like I said I just put in a new top end in it and got it re-sleeved.  Also, I just cleaned the air filter if that has anything to do with it.  Please help because I want to go riding before it gets to cold.  Thanks in advance.

Was it fouling before the new top end; or started after it?  What plug are you running in it?

How are you warming it up?  Could be loading the plug up, which causes it to foul as the plug isn't hot enough to burn off the deposits.  
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Dave H 2006 YZ250
(2008 YZ 125 son)

I am going to try to answer all the questions in this post:

I have tried to stay in the powerband as much as I can but some of the trails are technical so I have to stay in the low end.  

I have not done anything to the air screw and wouldn't know what to do with the air screw.  Can ajusting it stop it from fouling?

It wasn't fouling plugs before I did a new top end.  I think it fouled a plug when my top end broke though.  

How should I warm up the bike without "loading up the plug".

I will post my plug type when I get to my bike later today.  
03 YZ 125

Ok, turning the airscrew can only help so much, if it's not extremely rich, it could help. Turning it out will lean fuel/air mixture and turning out it will richen it. But don't turn it too much away from stock position though.

The jetting was probably changed for the previous top en, now that's it's fresh, the jetting is too rich.

And warming it up, anybody also post your warm up procedures.
Put the choke on, let it idle for about 30 seconds or abit longer, not too long. Then close the choke, then LIGHTLY(VERY) blip the throttle. Then (I) always leave it for about 2-3 minutes to just idle. After that i just start blipping the throttle lightly, and as it gets warmer, i give it more throttle till it feels crisp. Then i dont start riding it hard yet, i just slowly pull away and change gears just before powerband for about 3-5 minutes. Then i am sure the engine is properly warmed up.

I had the same problem, then i went many sizes smaller on the pilot jet, and some on the main. Since 4 months ago when i changed that, i havent fouled a plug.  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

My neighbor just bought me a NGK BR9ES.  I don't want to foul this one.  Where should I start?  
03 YZ 125

Find out if you have the standard jets in the carb.  
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Stand in the place where you are, think about direction and wonder why you haven't
North Carolina

Ok tomorrow I will take my carb apart and check.  Do they say the size right on them?  
03 YZ 125

There will be a # on them.  
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I love this dirt stuff.

should I check my needle position?  
03 YZ 125

Yeah check that aswell. and also which needle you have on(if it's stock or not).
There will also be a code on needle, like N3CW(just an example) etc.  
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2006 YZ250

- FMF Gold Series Fatty
- Yamaha Racing Graphics Kit
- Twin Air Filter
- Vforce 2 Reed Valves
- Clarke long range tank
- Cycra Handguards
- Longhorn Triple Clamps
- Pro Grip-Grips
- Pro Taper Handlebar
- Renthal o-ring chain and sprockets

I believe that you need a BR8ES standard plug or a BR8EG(racing plug)....The 9 is a colder plug and will foul easier.  My 250 requires the #8 plug so I would try the BR8EG or BR8ES..The G is a racing plug and the S is standard. (the G is twice the price)  Even if your bike takes the #9 plug, you can move down 1 # to the 8 and try that....