misfire! sputter

Joined
Sep 7, 2003
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#1
my 99 rm125 has been sputtering(misfiring). I was running at 40:1 just fine. I went from a 170 to 165, and middle to 2nd from top clip position. Now it is sputtering and missfiring at full throttle.
what could this be.
I am now running 32:1 MX2T with the new jetting.
 
Joined
Nov 20, 2001
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#2
grease,

You went back to your stock jetting and the same thing happens right?Ok,It could be a crank seal on the gearlube side or water pump side to make it smoke alot,which making it smoke bad.It also can be broken reeds.Its really hard to tell what the problem iswithout seeing or hearing the bike.Just make sure you have new plug,clean filter,check the reeds out make sure their in good shape.If it smokes bad,it could be the transmission seal bad,where it will suck gear lube in to the cylinder and smoke really bad.
 
Joined
Dec 24, 2001
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#3
Also go back to 40:1 as that should help lean out.
I have found when troubleshooting try only one
change at a time even thou it takes longer.
overbore.
 

Jaybird

Apprentice Goon
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Mar 16, 2001
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#4
Wasn't going to 32:1 leaner?

I would stick with a ratio and jet from there.
 
Joined
Apr 11, 2003
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#5
my advice is stick with 32:1 because by switching to 40:1 your just going to make it even richer. you might as well jet it at 32:1 instead of 40:1 to increase top end life. I used to think that i could disguise rich jetting issues by leaning out the ratio and it got me a destroyed cylinder.