Help? Zama C1Q carb idle circuit

[alexcagle]

I have a Stihl TS420 Zama C1Q-S118 carburetor, that I cannot figure out where the fuel feed for the idle adjustment needle is.
There is an idle circuit brass orifice (jet) with a check valve, which is needed in order for the remote purge primer to work. Beneath the idle jet, there is a hole drilled to feed fuel to the chamber containing the idle bleeds beneath the welch plug.
The idle speed mixture screw hole comes in the side of the idle bleed chamber, but I have drilled through several places to try to discover the feed hole. There is a tiny hole that goes to the area behind the needle, but it's got a plug in it.
Any help would be appreciated.

 

[alexcagle]

I have several other dead identical carbs that I drilled and sawed on to find any passageways that may supply the idle speed circuit needle. There were none. The tiny plug by the L side needle is to plug a drill hole to a cavity behind the needle, which normally could, I suspect, be a feed hole for fuel to the idle circuit.
The H and L are independent circuits as far as I can see.
I used a magnifying glass to search.
Could the needle be an air bleed?

 

[alexcagle]

What is the purpose of this plastic plug?
It runs almost the full length of the carb, and through the needle bores too.

 

[DND 9000]

The L-side fuel feed for the idle adjustment screw is under the inlet control lever (the golden jet with hole)

 

[alexcagle]

I concur.
But how can the L needle adjust the idle mixture if it has no fuel supply to it behind the needle to regulate ?

 

[alexcagle]

I think I just figured it out......
It flows from the idle bleeds chamber backward past the needle tip to the bleed hole that has the tiny plug.....
Somehow I never considered it could be designed to flow backwards.

 

[DND 9000]

Yes I see what you think. That could be the way for the fuel.

 

[alexcagle]

Thanks for the diagram.
It must be the main idle bleed and gets first exposure to the low pressure of the venturi, because if you close the needle, it dies.
*
The original issues with the carb was that it wouldn't idle at all. That leads me to think that I dislodgd the blockage when I flushed it with WD-40.
It runs great now.

 

[DND 9000]

That`s nice to hear that it works now. Sometimes it`s really hard to clean these carbs realy good, if some of these small passages and holes are clogged or patially clogged.