Where does the air go into the Idle Circuit On My 5HP Mariner Carb?

[Mark-1]

The carb is this one: 3303-812648T

I'm tinkering with my spare carb. Mainly for my own interest, but also to ensure all the channels are clear before putting it
In a zip lock bag until its needed.

I'm trying to work out where the air comes into the Idle cct.

I can see the pinhole near the engine inlet port downstream of everything where the mixture is introduced to the inlet. The Idle jet is upstream of this and doesn't poke into the venturi so I assume the Idle cct has its own completely separate mini venturi with a completely separate air inlet.

I'm expecting to be able to spray carb cleaner into the pin hole and see connectivity between the jet and the pin hole and and jet and the air inlet wherever that is and the mixture screws of course. I seem to have unobstructed connectivity between all the things I expect to be connected except wherever the air is coming in from. I can't locate that point.

Or does neat petrol drop out of the pin hole and get blown into the inlet by the bit of air that escapes through the venturi with the throttle shut? In which case all the mixture screw does is reduce the petrol? If that's how it works what does the jet do? I thought the whole point of the jet was to have petrol blow out of it by passing air in the venturi?

I may have completely misunderstood how all this works, in which case I'd welcome being corrected!

I hope someone can work out what I'm asking from this unintelligible question!

TIA.

 

[Mark-1]

Ahhh, I reckon my second theory is correct, and it works something like this:

https://www.carburetor-parts.com/marvel-schebler-idle-system

 

[Boathook]

During idling, normally the engine sucks the air in through the venturi with the idle jet supplying fuel. As the venturi is opened the air flow sucks fuel in via the main jet. Hopefully, the two running together supply enough fuel for full power.
Thats my basic understanding having stripped the carbs on my Malta a few times !

 

[VicS]

The carb is this one: 3303-812648T

I'm tinkering with my spare carb. Mainly for my own interest, but also to ensure all the channels are clear before putting it
In a zip lock bag until its needed.

I'm trying to work out where the air comes into the Idle cct.

TIA.

Here ?? if this is your carb (post 1987 2 stroke)

 

[Mark-1]

During idling, normally the engine sucks the air in through the venturi with the idle jet supplying fuel. As the venturi is opened the air flow sucks fuel in via the main jet. Hopefully, the two running together supply enough fuel for full power.
Thats my basic understanding having stripped the carbs on my Malta a few times !

I think you're spot on. Which explains why the Idle screw affects the Idle, rather than just the idle mixture screw and is good because it means no blockage.

 

[Mark-1]

Here ?? if this is your carb (post 1987 2 stroke)
View attachment 173610

Thanks.

I've sprayed carb cleaner in there and it didn't come out in the air inlet, plus it's the wrong end for air coming in. Not quite sure what that is, I think is blanked right off when the carb bolts on.

So, you've failed to solve my mystery and added a new one!