flyrotary@lancaironline.net Mailing List Archive

George, you're going to have to ask someone who has experience with carburetors - I went with fuel injection because of the very frustrating experience I had trying to tune a Webber carburator with all its different size air bleeds and jets. I just found EFI was much easier to know what I was getting. Not against carburetors, they obviously work quite well - if you know what you are doing with all the jets and air bleeds - which I clearly did not.

Perhaps Bill J can help.

----- Original Message -----

From: George Lendich

To: Rotary motors in aircraft

Sent: Thursday, September 27, 2007 3:12 AM

Subject: [FlyRotary] Carbs

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)