Yz 125 main jet 500???!!!

ajv#26
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ajv#26
Hello guys!! A few days ago l buy a used yz125 2010, and the bike was jetting like this: needle 3 from top, pilot #45, main 500, air screw 2 1/2... this jetting is for what? What is the effect on bottom end? I'm a bit lost here Dizzy
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FGR01
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FGR01 4/5/2017 7:42am
4/5/2017 7:42am
That jetting would be for ice racing with 2 mile long straights at -30 degC below sea level.
JW381
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JW381 4/5/2017 8:07am
4/5/2017 8:07am
FGR01 wrote:
That jetting would be for ice racing with 2 mile long straights at -30 degC below sea level.
Still might be a little fat on top.
ajv#26
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ajv#26 4/5/2017 8:51am
4/5/2017 8:51am
FGR01 wrote:
That jetting would be for ice racing with 2 mile long straights at -30 degC below sea level.
Laughing Laughing Laughing Laughing
scooter5002
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scooter5002 4/5/2017 10:52am
4/5/2017 10:52am
Or it has a leaking main seal, and the owner was trying to compensate for it, because he couldn't figure out why it ran lean.

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omalley
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omalley 4/5/2017 11:15am
4/5/2017 11:15am
Didn't Mikuni run a really high number main compared to Keihin? If memory serves, mid-400s wasn't abnormal vs 175-ish on Keihin due to their different numbering system.
ajv#26
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ajv#26 4/5/2017 1:24pm
4/5/2017 1:24pm
It's weird! The bike came whit a sand tire, and very hard suspension...
Next weekend l will try 40 pilot and 410 main and see the diference! Unsure
ajv#26
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ajv#26 4/5/2017 1:26pm
4/5/2017 1:26pm
omalley wrote:
Didn't Mikuni run a really high number main compared to Keihin? If memory serves, mid-400s wasn't abnormal vs 175-ish on Keihin due to their different numbering...
Didn't Mikuni run a really high number main compared to Keihin? If memory serves, mid-400s wasn't abnormal vs 175-ish on Keihin due to their different numbering system.
Yes, it is!
Rovalova
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Rovalova 4/5/2017 1:38pm
4/5/2017 1:38pm
omalley wrote:
Didn't Mikuni run a really high number main compared to Keihin? If memory serves, mid-400s wasn't abnormal vs 175-ish on Keihin due to their different numbering...
Didn't Mikuni run a really high number main compared to Keihin? If memory serves, mid-400s wasn't abnormal vs 175-ish on Keihin due to their different numbering system.
ajv#26 wrote:
Yes, it is!
Thats not unusual, A 420-430 is what is used a lot here in Australia, they are different numerically than Keihin, I know they use 480-500 in heavy sand desert style racing here, asked a few guys what they were running after my sons bike melted on the first lap with a 450 main
ajv#26
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ajv#26 4/5/2017 2:56pm
4/5/2017 2:56pm Edited Date/Time 4/5/2017 2:58pm
My bike came from france, and l'm living in Azores islands, so the altitude changes are bigger, l'm at the sea level, then five minutes later I'm at 800 meters of altitude, the temperature it's 9 to 27 celcius and humidity 50 to 100%
Set the jetting is a bit dificult here.
I always use im my bikes (2 and 4 strokes) the jetting spec of MXACTION, and it work and now l will try again because ride the bike whith the 500 jet is horrible, when she pulls it's like a rocket, but until there ist's a really hard.
Skerby
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Skerby 4/5/2017 8:15pm
4/5/2017 8:15pm Edited Date/Time 4/5/2017 8:15pm
I've run mine really hard in sand with a 430 main never had an issue. These were mid 50s (degress F) 37.5 pilot middle clip with stock 06 needle. After reading some of these comments Im thinking that may have been on the lean side of things! Still, I put around 15 hours on that top end with no issues, maybe high concentrations of 110 leaded saved me. I also run maxima super m premix which I have read has a very high flash point and works well for long periods of WOT.

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