Alright so I was running my YZ125 today, and I put in a lightly used BR8EG and the white part was golden brown when I put it in, and I rode for about 5 minutes and took it out and It was completely white, there is not oil accumulating around the silencer hole. This seems weird because today it was about 50 degrees, but the other day when it was about 35 to 40 degrees it was running fine and had alot of power. As far as I know I am still running on the stock jetting. This just seems weird to me, any thoughts?

btw: it seemed like it was running fine when i had a br9es and it even had some oil on it.

Yeah, sounds like the bike was running too lean. Maybe dangerously lean at 35-40 degrees.

Well it seemed to me like it was running fine when it was around 35 degrees, it was today when it was about 50 degrees that it seemed like it was running really lean, and what can I do to fix this?


Do not run a 8 series plug in a YZ125 in the cold. Otherwise, this could easily happen to you. :lol:

You need to richen your jetting to reflect what the days weather will be like. Forgoing this step could be costly. :worthy:

What do I need to change on the jetting?

What do I need to change on the jetting?

Put a 9 series plug back in. Fiddle with your air screw (turn inwards) to make richer. If not better, get a richer pilot jet followed next by lowering the clip one position on the needle and if your problem is in the upper rev range - go richer on your main jet too.

Way way more detail available here:

why would I have to rejet it richer?

why would I have to rejet it richer?

To alleviate the lean condition seen on your plug. If you're too lean with colder than normal air temps (for your jetting range) engine damage may occur.

But why would It run fine at 35 degrees and when its at 50degrees it runs lean? and would sta-bil in the fuel make any difference?

But why would It run fine at 35 degrees and when its at 50degrees it runs lean? and would sta-bil in the fuel make any difference?

It's running leaner at 50* now because you're running a hotter plug (8 series) than before with your 9 series at 35*. A nine series is a cooler plug. If it burns hotter than what it's designed for in your combustion chamber - it's gonna be lean even though the air temp has risen.

So all I have to really do is just run the 9 plug and it will all be good? Also, I think the bike is probably jetted for warm weather so should I run an 8 then or keep running 9?

^ Run the 9 and jet from there.

Ok, but if it is jetted for warm weather then can i still ride it safely when its kind of cold out?

Ok, but if it is jetted for warm weather then can i still ride it safely when its kind of cold out?

IMO, if you ride at 50* it won't likely seize with the correct plug (9 series), 32:1, and at least stock jetting values. Below 50* and you need to richen all circuits likely.

What plug do you reccomend for racing?


When I got the bike it had a br8eg plug in it and I rode it in temperatures around 30 degrees and it seemed to run fine, but then I put a 9 in it and rode it on that for a while and it seemed fine and when It was 50 degrees I put a lightly used br8eg in it and it was running lean, I just dont understand it, because I thought that when It was colder is when they run lean, but It ran fine it seemed to me like when it was around 30 degrees.


yeah br8eg is hotter that Br9eg so in warmer temps when running the Br8eg there is more of a chance to seize

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