Motorcycle Repair: Jetting for a 2002 Yamaha TTR-125, yamaha ttr 125, shively

Question
I have a 2002 Yamaha TTR-125E.  I bought it used a few months ago.  I live at an altitude between 800 and 1200 feet.  The jetting in it now is a 145.  Is this the right jet?  what should it have?

Answer
Hi Sean,

My calculations indicate a size 140 main jet.

At about 1000-1200 feet altitude, and guessing your environmental temperature is about 70 degrees Fahrenheit, and a correction factor of 0.96....the math says 140.


145 x .96 = 139.2 (140)

Respectfully,
Mark Shively