Fouling plugs like crazy out of no where.

YZ 125 2005 model

I'll run the bike for roughly 40 minutes or so and the bike will die on me. FOULED PLUG! fak happened several times out on the trails.

The original plug was a BR8EV i believe. I changed it out to a br9eg and it ran ok but the fouling started!

i ran a br8eg i believe it was and it ran nice but the power didnt seem to cut in.. like it was revving out super quick.

I've cleaned the carbs TWICE. I'm running stock jetting plus the needle clip in the middle position. running 44:1

what plugs are you guys running on a 05+ yz 125? maybe it's the plug or maybe i just over oiled the filter? dont think that could cause it to foul this bad.

This doesn't surprise me. A 9 is colder than an 8, and therefor more prone to fouling. However, a 9 is stock for your bie.

How hard do you ride? Are you really on it a lot cleaning it out? If not, then maybe the hotter plug is right for you. If you do ride hard, I would stay with the stock heat range.

If I were you I would also run something more in the 32:1 oil/fuel mixture. 125s are hard working little engines, they will take all the extra protection they can get. It also will lean the air/fuel mixture very slightly, helping your fouling problems.

A bad reed will make it rich in the lower rpms.How does it idle?

Poss. r/h case seal bad?

What elevation and temps are you riding at? Both will affect your jetting.

I'd go with the stock recommended plug, unless you are really lugging it down low al of the time and never revving it out.

Don't overlook excess oil on the air filter. If you are spraying the filter with an aerosol product, then you probably won't have a problem. However, if you are dipping the filter in your oil, then you may have excess oil in the filter. The filter should be slightly damp with the oil, not dripping wet.

jetting.re jet it and give that a go-could also be the tempture

A bad reed

Yep...

i dont really lug the bike around low.

Usually at least half throttle all the time and constantly blipping the throttle.

Maybe i'll stick with the 8 since it runs better on it.

I was always confused about running more oil. Doesnt that mean there is more oil that cant be burned up causing more gunk? there's less gas, but more oil that isnt burning up.

I ride at roughly 4500-5000 feet

The idle isnt that bad although it doesnt idle for a long period of time. The idle is set low.

R/h = right hand crank seal?

As for the reed i took them out and looked at them. no visible. cracks or anything

Your pretty high in elevation for stock jetting. Have you always ridden at that elevation, or is this a new riding area for you?

Blipping the throttle won't clear it out. You really need to pin it and go for a few hundred yards at a time. Small 2t's really prefer to be revved (especially the MX bikes).

I've had the same problem. there is a great article on rejetting and setting the float level (probably the real culprit) on yz125's, look it up

I've had the same problem. there is a great article on rejetting and setting the float level (probably the real culprit) on yz125's, look it up

thanks!!! Read through it and it seems i've got some work to do! =) probably have to do a new top end and reeds first before jetting

If I were you I would also run something more in the 32:1 oil/fuel mixture. 125s are hard working little engines, they will take all the extra protection they can get. It also will lean the air/fuel mixture very slightly, helping your fouling problems.

while your doing your work this is a good ides 44-1 is not the best by far, change your premix and get it jetted while your doing your other stuff. GL

Well if it was running OK before it started to fowl plugs sounds like a dirty airfilter and or float adjustment. You probally keep the air filter clean, so then I think your problem is float adjustment.

i dont really lug the bike around low.

Usually at least half throttle all the time and constantly blipping the throttle.

Maybe i'll stick with the 8 since it runs better on it.

I was always confused about running more oil. Doesnt that mean there is more oil that cant be burned up causing more gunk? there's less gas, but more oil that isnt burning up.

I ride at roughly 4500-5000 feet

The idle isnt that bad although it doesnt idle for a long period of time. The idle is set low.

R/h = right hand crank seal?

As for the reed i took them out and looked at them. no visible. cracks or anything

try running less oil, i always run 2 oz of yahamalube per gallon, the fuel is what cools the engine not the oil. too much oil is useless, if it dripping from the head pipe or any place else your wasting it , i raced off road for 16 years and never ran over 2 oz's and never had a oil related issue with a engine, never fouled plugs either

I have a 98 that had the same problem. I went through the same process of cleaning and jetting with no change. finally, I read a jetting article in thumper talk and discovered that the float level can cause the carb to run too rich sometimes due to a worn needle. replace the float needle and reset the level according to the manual and all will be well.

you need to clear it out more, if you are running at half throttle it will just load up and foul the plugs. Go a gear down and ride it like a 2-stroke...On the PIPE!!

your really rich at 4500 feet....

I run a 400 in the winter as the mj here in tex and a 390 in the summer with a 35-37 pilot on C12.

You could easily drop the mj to a 390 if not 380 and definately the pilot needs to go leaner....try a 35.

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