My bike is PX125. MY bike used MALOSSI 166(not porting), SI 26e or Si 24e and RZ MARK ONE.
I want to ask that which type of JET(be3 or be4)  ,Idle and main JET can use for my bike ?

Thank You. 

Plug read first to determine the condition (rich or lean) of your motor. Use new plugs when doing your plug reading. This should give a clear indication of the condition your motor. After seeing the results, you can adjust the pilot screw or change the size of your main jets.

p.s. avoid the 26/26E carbs they can be very temperamental to set up.

Read the plug, also do a ‚plug chop‘ so that you make sure it doesn’t lean out when you rev it out. If your using a SI 24/24 E, the mixer tube is BE3 normally. Unless of you have changed that or the previous owner has.

A standard P200 24/24E carb works well on a Malossi 166 but taking into account the [superb] RZ righthand pipe I would suggest standard P2 settings but main jet up to 122 and then check your plug colour for fine adjustments.