Subject: Holley Carb
From: rotaryeng
Date: 9/12/2013, 2:42 PM
To: AAA-rotaryeng


       There was discussion on a fuel cut off kit for the Holley carb. I was thinking EFI at the time for my installation so I didn't look at it very well. Now I am reconsidering. Can the fuel cut off be used for leaning? Who sells this kit? Thanks.

       Paul Shamlian


       Tom McNeilly <tomcn@earthlink.net

       It is more than a fuel cut off. You can lean the mixture.

       Here are some 3D's. The 500 CFM 2 barrel is about right for a P-port
       13B or RX8 engine.


       What kind of airplane are you building Paul?

       Paul Lamar

--------------------------------------------------------------------------------------------
       "The mixture control body is CNC machined from 6061-T6 aluminum which is
       alodine treated, the shaft is stainless steel and the screws are plated
       steel.

       The first picture is what comes in the kit. The mixture control plate is in
       the background with the accelerator pump extension arm., power valve block
       off plug, and installation bolts in the foreground.  I also include a set of
       three gaskets which are not shown.

         The second picture is a unit installed on a 4 barrel Holley carburetor.
       The installer is responsible for the push-pull cables and attachment
       hardware.  As you can see, the unit is installed in-between the jet plate
       and the float bowl.  This requires the use of longer float bowl bolts which
       are included in the kit.  The arm swings through 90 degrees of rotation from
       idle cut-off to full rich. The arm can be clocked anywhere on the shaft to
       make installation easier.  The arm in the photo is in the full rich position
       and idle cut-off would be in the 4 o'clock position. Two shafts are available
       to make full rich either in the clockwise rotation or counter-clockwise
       rotation.  This sometimes simplifies the push-pull cable installation.  I
       usually ship the counter-clockwise to full rich shaft, as this parallels the
       throttle rotation on the opposite side of the carburetor."

       Tom McNeilly <tomcn@earthlink.net <mailto:tomcn@earthlink.net> <mailto:tomcn@earthlink.net <mailto:tomcn@earthlink.net>> <mailto:tomcn@earthlink.net <mailto:tomcn@earthlink.net> <mailto:tomcn@earthlink.net <mailto:tomcn@earthlink.net>>>>
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       The plane is a Bearhawk Patrol. It will be used for off airport and high altitude mountain flying.

       Paul Shamlian


        It will be spectacular with an 80 inch prop, a 250 HP p-port engine and a 3.12:1 gear box.
       A 500 CFM Holley 2 Barrel carb will work fine. Plenty of room under the cowl.

       When we get the new Outboard/Vespa style ignition working it will run with out an electrical
       system and/or battery.  Just like a Cub. Gravity feed fuel tanks.

       Tell Bob I said hello next time you speak to him.  I usually see him at Sun n Fun and Oskosh
       when I was still going :)

       Paul Lamar


   Can the engine be hand propped with the PSRU? Seems like the PSRU would not only triple the amount compression strokes in a swing of the propeller but it would also triple the amount of pressure to get through each compression stroke.

   Paul Shamlian

   My guess is the prop will not have enough inertia to drive the engine through the 3.12 step up gear box.

   Maybe a rope starter could be made to work. Tie one rope from the right side engine to a stump and the other around a pulley on the e-shaft nose. Getting a running start off to the left of the engine.  Works with outboards.

   I am only half joking :)

   Paul Lamar



Paul Shamlian,

Since my engine is not ready to run yet, I turn it over every week with corrosion X sprayed in the intake, with a 2 x 4 a little bit shorter than the future prop. Here is what I can tell you: Yes the gear box does take a bit more effort to turn the engine than a "regular" airplane motor, but the engine is turning over 3 times as fast. On a regular airplane engine, you would grab the blade and pull through one, two if you are lucky, compression strokes before you let go and run. With the rotary, this same prop distance results in 1. 3 times the engine rpm, and 2. more firing events.
The normal 4 stroke piston engine- say a 4 cylinder lycoming- will fire each cylinder every 720 degrees of crank rotation. Divide this by 4 and you get 180 crankshaft degrees between firing events.  If you grab the prop at 10 o'clock and pull it through, you might get 90 degrees before letting go, so you start right at the bottom of the compression stroke and hope it fires.

With the rotary and the 3:12 gear box, this 90 degrees is now just over 270. The rotary fires each face of the rotor every 180 degrees of crankshaft rotation. With a 2 rotor, this is a firing event every 90 degrees of crankshaft rotation. For the same 90 degrees of prop travel the engine goes through 3 firing events. 3 times more chances for it to start. So, instead of pulling one piston through, you pull in effect 3 for a little more effort.

Kind of like Paul's reference to the rope starter on your lawnmower. You could (in theory) start your mower by yanking the blade through one compression stroke, but the effective gear reduction of the rope starter and its multiple firing events per pull make starting much easier.

Kevin Alderman




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