FMX main jet

[kubakruk]

Could you please write me what is the original size on main jet in FMX? What the biggest size I can use?

[Bobn]

I believe the standard is 165.
You can go up to 175 on open pipes or 170 on slightly de-baffled pipes.
There's no point putting a bigger jet in unless you open up the pipes, or change to free-flowing ones.