Zama C3 with 18,8mm bore/venturi?!

[Maxchaos]

Hello!
I'm following the forum from a long time,but now I need an help for something I can't understand.
I'm rebuilding a 357xp,It has a farmertec crankshaft so I bet the previous owner had thinkered with It. I've deleted the base gasket and used a new Meteor piston.

It run very strong and I Can tune the carb good,but it's lean at low,I've turned the screw 3 turns out but It still wants more and more turns make no effect. On the H side I can make It 4-stroke at 2 and half turns out,maxing at 12500 rpm.

I tought carb maybe is the problem,so pulled It out to check wich model It have.
I can only read Zama C3-13a but seems It doesn't exist. The carb hole diameter that goes toward the cylinder measure 18.8mm diameter,is this the commonly called venturi size? I can't find any carb with so big diameter,any help?
The saw run very strong at wot,but doesn't sound fine at idle,seems lean. I Will probably buy a Zama c3-el42 for now. But i'm curious about this very big carb, it's definitely bigger than the el42 that I have on 346xp.
Thanks for any input.

 

[huskihl]

The Venturi measurement is the number that is normally referenced. It is the small inner diameter of the throat in the middle of the carburetor

 

[Maxchaos]

Oh ok thanks,so it's the internal "throat". I measured the new HDA198A that I bought right now and it's 18,9mm at the cylinder intake so i'm measuring the wrong spot for the venturi.
Hopefully this carb work good now.