While designing this carb I needed to know what to expect
 in terms of fuel flow and mixture as I changed the pressure
 inside the fuel chamber. This is the pressure difference across

one main jet. Some is due to lower than atmospheric  pressure in the venturi

and some is due to the higher than atmospheric pressure in front of the diaphragm.
 It is the difference between these two that flows the fuel.

 I was amazed that such low pressure difference
 of .5 psi can change the flow so drastically.
 This is  based on a formula that Kinsler had in their
 catalog and a chart of water flow for different
 size main jets. The jet size chosen here for starting
 purposes is .079 inches in diameter. The rotary will run
 up to a mixture ratio of 17:1.


New flow = old flow times the square root of new pressure divided by old pressure.


 Here is the data, the program and the flow charts it was based on.
 Check my math.

 All of this is ground adjustable in my design including the main jet area
 for each rotor.

 The spring force on the diaphragm will initially cause the pressure
 in the fuel chamber to be in the range of 2 psi. The fuel pump pressure
 will be higher than that of course or you would not be able to fill

the carb with fuel. As the spring force is reduced by a manually controlled
 cam the pressure in the fuel chamber will lower leaning the mixture. This
 is very similar to the way Dial A Jet works.

 This should be a relatively low cost, very effective
 and very reliable carburetor with so few parts of any kind.

 Paul Lamar ...No rotor no motor.

Hi Paul,

If I understand all this correctly the lever will have to have a very
fine micrometer type adjustment to handle the large mixture swings
created by only a very small delta P change. Looking at the charts and
working backwards we know the mixture ratio will never need to be under
~12 so starting there this would be 83 #/hr or 14 g/h and utilize a .070
dia orifice instead of the .079, not really a whole lot of difference
but it might help to make the adjustment a bit less touchy. The ratio
could even be pushed ~14 and an even smaller orifice used. Would
this effect other parts of your overall
plan?                                      Dave M


Yes I am still working on the eccentric cam design that adjusts the spring force
so I can set the lever movement angle change to about a 90 degree travel.
Of course the springs can be changed too during R&D.

Paul Lamar ...No rotor no motor.

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