Does anyone know how to work out the cross sectional area of a main jet?  Or does mikuni have a site that will tell me the sizes?  Just curious.

Are you referring to the size of the main jet's orifice?

A= Pi * r**2.

r = d/2

where d is the Mikuni jet number.

Quote from: KevinCA= Pi * r**2.

r = d/2

where d is the Mikuni jet number.

Thanks for that.  I have the basic math, just needed to know exactly what is measured and in what units.  WRT the Mikuni jet number, is that in 1/1000s of an inch?   IE is my stock 115 therefore 115/1000" diameter?

Should have asked how the jets are measured then, not how to calculate the area.

A Mikuni 125 jet has a 1.25 mm hole for the fuel to flow through. I have had some trouble verifying this. Other jets (like Dynajet) have a proprietary numbering system that doesn't seem to easily relate to anything.

Pretty unlikely anything will be in inches except for the US and Uganda..

DJ and mikuni and keihein all measure jet diameter and say it without the decimal. I have stuck drills in these (you need those alphabet drills for it) and measured the diameter with a vernier for added accuracy. They all are the same and they all say diameter in mm wihtout the decimal. However some slight variations in threads exist between mikuni and Kehein. I have still put one in the other first by accident nd then on purpose but I found some small brass slivers the first time. I then checked the threads and cleaned them all with a tap and they all fit happy. Then when I did the next size with the wrong jet a comparison of threads showed slight differences. Needless to say tapping them takes cre of it...
Like the ad says Deep down they are all choclate...or in our case diameter...
Cool.
Srinath.

Quote from: KevinCShould have asked how the jets are measured then, not how to calculate the area.

A Mikuni 125 jet has a 1.25 mm hole for the fuel to flow through. I have had some trouble verifying this. Other jets (like Dynajet) have a proprietary numbering system that doesn't seem to easily relate to anything.

Pretty unlikely anything will be in inches except for the US and Uganda..

Yes, I guess I should have been more specific.  Thanks for the reply- it's just what I was after.  The inches thing was a guess, given that so much of the stuff made is influenced by the (large ) US market.