How do I...

[inanecathode]

Go about finding out where to buy a smaller main jet for my xt250?

I know i need a size 160 as apposed to the 165 equipped ( i ride it at 8000 feet and higher ).

The carb is a mikuni if that helps...

[h2olawyer]

Dealers may be a pain, but remove the jet you have & take it with you to a dealer.  Show them the jet & ask for the size you want.  That way, you get the right type of jet - there are a couple different styles for Mikunis.  Shouldn't cost too much.  The Yamaha dealer here has a large clear plastic divided box with all jet sizes.  they  just grab one out of the box, confirm the size & sell it to you.  Easy - other than the fact you're at the dealer.  Most independent shops should have them as well.  You might call around first, just to make sure.  They're also available mail order / internet from sources like Dennis Kirk.

H₂O