I have an old Snapper mower with B&S 3.5hp engine that I am working on. See attached picture. It has a carb that has a throttle mechanism/linkage that should engage and disengage the choke, but I can not figure out how it works.  See image.  The yellow arrowed linkage should engage the red arrowed choke.At first I thought the black plastic choke top (red arrow) was broken.  But the few parts diagrams I see - it looks okay. So I wonder if the throttle piece (yellow arrow; has two metal arms) is missing something. Any and all help appreciated.

Here's a diagram for your engine but the linkages don't look the same to me?? https://www.partstree.com/models/121702-3132-01-briggs-stratton-vertical-engine/controls-4/ 
In this parts list it shows a choke lever and spring (Part # 494218) which would move the clutch.
https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/100000-19z999-series/121700-to-121799/121702-3132-01   The lever would not be practical on a lawnmower (As they are usually controlled by a choke cable you can move from the operating position). Do you know if the engine is original? Is this a riding or push mower? Good Luck!

Thanks "Thesmallenginehobby" for the reply.  I saw that parts diagram and agree the parts do not like identical.  And regarding that spring - it may be missing ... but I'm not sure where it would connect.  The weird shape of the choke control top is really throwing me.  But I've look at other carbs an eBay and they have the same shape.
It is the original engine and it is from a Snapper push mower.
 
If all I'm missing is the spring - I could get one - but I'm at a loss as to where to connect it.

I've NEVER seen a spring attached to the choke to operate it.  Soo forget that.
 
With that said, when the "control bracket" (that rotates with the handle throttle)
SHOULD engage with the choke when the handle is pushed all the way forward 
activating the choke. 
 
Yours looks somewhat mangled so some tweeking may be needed..
Again, with that in mind, rotate the control plate past full throttle, where it
should engage the choke.  At the same time watch the choke plate close.
 
They should mesh together, so re-set (loosen the carb) so that both above
listed parts mesh together.
 
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I found an old picture that shows the spring in place on the choke.  Still not sure if the geometry works.
I need to get a spring or do some more testing.  Still does not seem right - but this is the way it was when I got it.
I wanted to attach the picture - but the forum does not seem to be accepting it right now.

I believe the arm (yellow arrow) is bent.
 
It very likely needs to be on THE OTHER SIDE of the black choke lever.
So when the throttle is pushed all the way forward, the throttle is wide open and the choke 
plate is NOW CLOSED...
 
Un-bolt or at least loosen the carb and make that tab is straight.
 
Slide the carb back on (manipulating it in the correct position)
making sure that tab is on the other side of the choke lever..
 
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I took Scott's (STRsFZ6) and bent the arm.  I found a position I think will work.
I was having such a challenge uploading links here - I will try to link to my image server.  I hope this works.
 
Here is the most original picture I have that shows spring:

http://0zero1one2two.tplinkdns.com:2283/share/5CgQrBJt-yzJJbWfzFwEB2tv3kFI3EWiSSVfo9eqqPvprRkC0AsdCevr8JdaKNX7-_A
 
Here is a video I made today with the throttle control arm bent in such a way that I should get proper choke movement:

http://0zero1one2two.tplinkdns.com:2283/share/Bww5XpjLiofUyvqCqciZgQRRSqkaXLryjo3Nqh_QLs1Spem37LTd16Ux7tAgZwP_zHA

Your video looks like it's working properly now.  
 
Choke is closing fully when the engine linkage is pushed fully, correct?
 
Might want to brake clean all that nastiness atop the carb and linkage assembly..
 
 
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Yes - thanks for all the help.  I was waiting to clean up/paint the engine and mower until I felt I could have a properly running system.  Now that I think I can - I'll clean things up and then re-assembly.  
Thanks for all the help.

Yepper,  Have fun!!
 
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