Mccoy throttle question

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Mccoy throttle question

Postby linktrain » Tue Jul 11, 2006 5:55 pm

I have a Testors Mccoy .19 Blackhead.
On the needle side of the throttle body there is
a rotatable brass disc with an index dot on it.
There are three scribed lines on the throttle
body near the index dot on the rotatable disc.
What is this disc called, and what is it's purpose?
As far as I can see it's only purpose is to cut off
the fuel supply, but maybe it does something else.
Can anyone explain?


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Postby loucrane » Fri Jul 14, 2006 1:23 pm


That is most likely a Perry carb. They were very good when abundant and popular. Got a bit pricey, and engine mfrs went to own design more than 3rd party.

To set up: Set the line on the brass disc to the center line on the black carb body.

Presuming you have enough time on the McCoy that the Dykes ring is seated and the other wear-in bits are happy with each other...

Start the engine and get a nice two-cycle at wide open throttle (WOT). This needn't be the ultimate, at the point of sagging lean, just well up in the main needle two cycling range.

Ease the throttle back down to idle. From here it is much like setting idle on any carb (or is that: carby??) except that you trim the idle setting by moving the brass disk VERY slightly off the center line.

The symptoms are the same: stopping, gagging on smoky exhaust on throttling up suggests rich. Sighing to a dry smokeless stop on throttling up, lean.

Of course the throttle stop screw may be too far closed... To preclude: leave a visible eyebrow opening at the stop. Later, once you're near set, you may be able to bring it further in.

The brass disc is coined around the edge, right? By 'small movement to adjust,' I mean you to think one or two coining ridges at a time. There should also be '+' and '-' marks stamped alongside the line on the brass disc. I don't recall which means what, but in trying to stabilize a decent idle you'll soon find out.
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