Ed,

I have another one for you!

I am currently copying some of the parts of different carbs to cobble together my own design. I found info that the slide carbs with the flat ground needle - have a needle size of 1/8" ( 3.175mm) and are ground to what appears to be 'half' their original size at WOT. My needle stock is 3.18mm, with sliding tolerance, the needle seat/ jet is 3.23mm

 

That is the sized used for a 38mm carb and I was wondering if the 44mm carb might need a bigger needle, but I don't know how to calculate the main jet size/ fuel flow.

 

I have 13.1936 lbm (min of air) and 1.043lbm (min of fuel) at 12.65:1 fuel ratio, at 7,500 rpm (WOT).

 

Can you show me how to work out the main jet size please, I just need to know if I'm in the ballpark or need to go up in needle size, if the depth of the grind exceeds 'half' the needle size at WOT.

 

George (down under)

 

 

When we had SUs, we put motor oil in the slide dampers, and filed flat spots on the back of the needle to change the fuel supply,and raise and lower the needle in the slide.  Most Race car stuff is just wide open with good transition from zero throttle to wide open suddenly with no missing. Aircraft is easier yet with 98% of the time at wide open, with lots of time to write down O2 readings and EGTs to make changes later, or tailor your leaning system.

 

Lynn E. Hanover