This is pretty self explanatory.
To lean the carb you move the entire float
bowl up and down.

It is mostly made from Holley stock parts.

BTW Mark S, if you are building a P-port from scratch
you could keep one small side port for each rotor
for the idle system.

Paul Lamar

Paul,  It would seem that the slide  would be the throttle plate
for the
carburetor and that a similar slide choke plate would eliminate the
drag
of the choke plate at WOT.  As for the restriction of the venturi
making
the intake diameter effectively smaller you might use a booster
venturi
which is removable on several brands of carburetor and allows intake
 area  around  the outside of the booster.

George grimes


Thanks for the suggestions George. Can you make a 3D for me?

Paul Lamar


Paul, In the 60's  Chrysler built 413 cu in wedge super stock engines
with 31 inch long tuned runner between the
4-barrel carbs and the intake valves.  The carbs were located on the
opposite side of the engine so as not to affect the tuned length that
ended at the throttle plates.  If the proposed 1-barrel is close to the
slide throttle wouldn't the venturi  negate the tuned length runner
benefit?  I see this as a different condition than the slide throttle
being in the runner at 75% power cruise HP.  There may be some effect on
the resonant pulse but only at reduced power. At WOT it is not in the
runner but the carburetor venturi would always be present..I can
understand that throttle response on a road racing car is important and
having the volume below the throttle at a minimum helps the throttle
response but that is irrelevant on an aircraft engine.
George grimes

Yes and that is why I moved it out to the ends of the tubes  in the
latest iteration. Actually since we have HP to burn it might not bother
the tunning enough to mater when mounted close to the slide.

When the carb is near the  input end of the tube you get a lot of fuel
vapor stand off so one must use a sealed ram airbox. See this You Tube
video.

http://www.youtube.com/watch?v=NKJ00JsnS8A

Paul Lamar
Paul,

There are several version that you have posted.  Could the venturi be
located close to the slide throttle?  Why not use one bowl and float
with 2 needle valves between the two runners? Reduce parts count.  Is
the the slide throttle the throttle plate in the carb scheme?  I need a
fuel system soon and always liked the carb for simplicity.

Joe Berki
The reason I went with one float bowl per throat was for capacity
reasons. One Holly float bowl per two throats would be fuel
limited. You get two float bowls with every Holly 4 barrel.

As George pointed out... not a good idea to put the carb
next to the slide. It ruins the tuning to a certain extent.
Paul Lamar


Paul,

The carbs could be located at the inlet to the runners with a sealed plenum feeding the carbs.  Can they be lower than the slide throttle? Does the carb only have a choke butterfly now with the slide becoming the throttle butterfly?  Thanks for  any help.

Joe Berki


Sure they can be lower than the slide throttle.
No choke is needed on aircraft carbs as they are started
full rich. It is only in cars where the driver never controls
the mixture that starting chokes are needed.

Also there is another point about this particular scheme
of actually changing the float level over a wide range.
It is fundamentally different and superior to the usual leaning method
of restricting the size of the jet. At very low power and air flow levels the suction of a venturi falls off disproportionately with airflow. With a movable float bowl you can actually cause the fuel to dribble into the engine with no airflow at all. If you mount the carb lower than the port this won't happen. The fuel will merely run into the sealed plenum. A simple stop screw can also adjust the upper position of the float bowl to prevent this from happening.

Another trick is use air bleed to improve the BSFC but that requires a somewhat more complicated feed tube. More about that option later.

Paul Lamar