Stihl MS181 weird manifold

[pozidriv]

Hey,

I've come across this forum a couple of times before, while fixing stuff, but this is my first post

I'm trying to repair a small stihl ms181 for a friend. It has this weird style of manifold and two butterfly valves on the carb leading up to them:
Three holes in the cylinder head: inlet, pulse and???

The carb:

What does the upper butterfly valve do? It opens along with the fuel valve and it seems it just lets air in somewhere?

So I'm just trying to understand the function of these parts.

Thanks in advance!
Kind regards

 

[RED-85-Z51]

Stratocharging port

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[RED-85-Z51]

Blue is straight air..no fuel

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[pozidriv]

Stratocharging port

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Thanks! Something to google

Edit: that little clip is even better Had no idea something like this existed.

 

[heimannm]

That is a "strato" or "stratocharged" saw. Basically it is designed to put a layer of fresh air on top of the fuel/air mix in the cylinder to minimize emissions of unburnt fuel.

Mark

 

[pozidriv]

Thanks for the replies!

So I guess the air gets 'stored' inside the upper cavity, which then passes the transfer port first?