I have asked Revmaster for air flow and velocity figures, but these may be derived from piston engine type figures.

 

If you or Lynn could comment on this it would be greatly appreciated.

 

Also my research indicates that flow air/ fuel mix richens at higher RPM and altitude. I can't remember why at higher RPM - mind block, however for altitude it is because fuel flow is driven by air flow and even though the density of the air is lower ( at altitude) the flow remains the same - therefore richer mixture. Revmaster says their needle design is self leaning ( to a degree) because of design. I assume because the air density directly affects the suction to the rear side of the flat ground needle, ( this provides the low pressure area rather than the venturi) therefore with reduced density you have reduced suction and reduced fuel and leaner mixture. However I will clarify that when next we talk.

I find this all very interesting!

George ( down under)

I have missed the question.

Carbs get leaner near the top of their RPM ranges and use a number of tricks to maintain a reasonable F/A at high RPM. Even Webers with a huge number of emulsion tubes and jets for any imagined situation. If you actually remove the venturi (called the choke) from a carburetor it no longer will develop any differential pressure, and no fuel will flow through it.

None is way too lean.

More like the Bendix dribble fuel injection that is based on a positive displacement pump geared to the engine. It just pees fuel all of the time. Crude but effective.

 

In many cases of a slide and needle type of carb, the edges of the slide hole and the flat shelf the slide seals against, is more than enough turbulence to form the choke. Like Posa, Stromberg, SU and any motorcycle carb. They all have chokes even though it is not obvious. 

 

A 12A dyno sheet shows 139.6 foot pounds of torque at 6,500  RPM. and 173.3 HP. This is an engine designed for 9,600 RPM shifting. This has a Weber carb has two 36MM chokes. Two 40MM chokes would be real nice. Longer runners would be better, so cruise RPM is also the peak torque or a bit above peak.

 

Lynn E. Hanover