Dave,


I understand perfectly how a two-needle carburettor works.

What I don't understand is your claim in post #39 that the main needle controls 90% of the carburettor's function...

Would you care to explain how does it, for example, tailor the fuel curve for the engine's decreased fuel needs at 1/4, 1/3, 1/2 throttle?...
Oh, there is no explanation for this?

That is because it doesn't!

The low-speed needle's taper, in conjunction with the fuel nozzle's tip, is what controls this function.
This is done, as Webra did not care to explain, as the diagonal locator slot in the carburettor barrel causes it to move into the carburettor body, together with the low-speed needle, as the throttle is closed.
The needle's taper moves about 2 mm into the nozzle, as the carburettor barrel is rotated from fully open to idle.

Contrary to what you wrote, the low-speed needle moves much more than does the high-speed needle. And its movement is directly controlled by the throttle.


Maybe you, like Webra, chose the wrong wording... The 'main needle' (for which I prefer the name 'high-speed' needle) does control the fuel mixture at 90%-100% open throttle; not over 90% of its range.

Please read what I wrote in post #38 again, as to the interaction of the low-speed needle with the high-speed needle.

This is not meant as an insult.
Understanding this should clear up many misconceptions.


I stand by my claim that this part of the Webra manual is incorrectly written, uses incorrect terms and does not explicitly illustrate the function of this excellent carburettor.


In the mean time you can practice 75% throttle landings (it is within your definition of Webra's 'idle range'. No?)...