> It is coming right along. We found a center less grinding
> outfit 10 miles from Santa Paula in the small town
> of Fillmore Ca that has agreed to do a range of fuel needles
> for us. Very convenient. The precision of this
> needle is crucial. One thousands of an inch difference
> of diameter can result in a change of fuel/air mixture.
> The grinding outfit can hold 1/10 of a thou accuracy.
> We will have a range of needles that we can change
> during the dyno test until we find one that gives a
> reasonable mixture across the RPM and load range.
>
> If anybody wants to build one of these my friend
> Jim Poole can machine the hard part for you. Fortunately he
> has a right angle milling head for his Bridgeport mill
> as that is what it takes to drill the long needle hole in the
> slide. There is not enough vertical travel in the mill head
> and foot.
> -- > Paul Lamar ...No rotor no motor.

Paul,
Looking good, however I can't understand why you need a number of needles
when only one would do if you adjust it with a threaded end - especially
since your taper is totally linier. It seems an overly complex way of doing
it to me.

I have my needle seated on a spring and a threaded rod that pushes on the
needle guide. The spring keeps the needle and guide positively positioned
against the threaded rod - which also acts as the throttle.

Turning the rod pushes the needle and guide up and down, leaning and
enrichening - pushing and pulling on the rod is the throttle control. With
one knob you can throttle and lean, at the same time if you want to.

Attached is a photo of the needle in guide (slide carb 13). The spring
slides over the needle and sits under the guide, the needle and guide slide
into the slide plate (slide carb 18). Again in 19. There is a top plate
with
a threaded centre hole which the throttle rod screws into and pushes on the
needle and guide.

Can't get much simpler than this!

George (down under)

George,
Paul's comment about the need for various needles is correct. The fact
is that various engines in different states of tune need to change in
richness at different rates. Look at a standard carburetor and think,
the guys building this thing are trying to make a PROFIT. The point is
they wouldn't be putting double taper needles in there if they weren't
forced to because of engine function. The aircraft carb will probably be
able to get by with one needle, once the proper taper is determined. The
back flow, or revisions at certain RPMs can literally stop the engine if
the throttle is held at a specific opening that causes problems. I had a
engine that I built for a guy that had a "point" in the RPM range where
you could literally take the engine into a nonoperable mixture by
closing and then opening the throttle. The engine would simply stop. It
this case around 4000 RPM. The problem was unrecoverable, that is once
the engine bogged is was going to stop. IF you ran the engine directly
through that range it would scream to redline. The point is that the
system is complicated. Sometimes we tend to gloss over the necessities.
Bill Jepson



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