Zenith 161 Idle Fuel Pickup Passage - Size

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   The 11141 carb on this CA I am going through has the threads stripped out for the main passage plug. I have a pretty rough 9705 carb (from a C, I suspect?) that I was planning on stealing the bowl from. I'd swap the threaded main jet, well vent, etc. parts over from the CA bowl to the C bowl, and then use the original CA throttle body.
Then I noticed that the idle fuel pickup passages drilled into the bowls are different sizes, and the CA/11141 has a brass orifice installed. The C/9705 has no orifice. Since the drilled holes are different sizes the brass orifice from the CA would not fit into the C bowl.

How important is this orifice? I would've thought this was mostly irrelevant as the idle jet sizing controls flow into the throttle body. However... I also doubt Zenith put that orifice in there just for fun and extra cost.

CA/11141 carb:

C/9705 carb:

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wjohn Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 19 Jan 2010 Location: KS Points: 2317	Post Options Post Reply Quote wjohn Report Post Thanks(0) Quote Reply Topic: Zenith 161 Idle Fuel Pickup Passage - Size Posted: 02 Jan 2026 at 11:11pm
	The 11141 carb on this CA I am going through has the threads stripped out for the main passage plug. I have a pretty rough 9705 carb (from a C, I suspect?) that I was planning on stealing the bowl from. I'd swap the threaded main jet, well vent, etc. parts over from the CA bowl to the C bowl, and then use the original CA throttle body. Then I noticed that the idle fuel pickup passages drilled into the bowls are different sizes, and the CA/11141 has a brass orifice installed. The C/9705 has no orifice. Since the drilled holes are different sizes the brass orifice from the CA would not fit into the C bowl. How important is this orifice? I would've thought this was mostly irrelevant as the idle jet sizing controls flow into the throttle body. However... I also doubt Zenith put that orifice in there just for fun and extra cost. CA/11141 carb: C/9705 carb:
	1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45

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Les Kerf Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 08 May 2020 Location: Idaho Points: 1510	Post Options Post Reply Quote Les Kerf Report Post Thanks(0) Quote Reply Posted: Yesterday at 9:58am
	I would just give it a try and see what happens

wjohn Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 19 Jan 2010 Location: KS Points: 2317	Post Options Post Reply Quote wjohn Report Post Thanks(0) Quote Reply Posted: 11 hours 31 minutes ago at 10:26am
	I actually have to correct myself - upon further inspection, it is not an orifice but I believe a brass tube inserted into the bowl casting. I am not sure why that would be needed unless they had issues with the casting in that area? Based on that I am more confident I could swap bowls. I am trying to see if there is anything creative I can do to salvage the original bowl before I totally abandon it. I could try a 3/8-24 bolt that is slightly longer than the Zenith plug to grab a couple more threads. There isn't a lot of room to work with before you would be blocking off the outlet from the bottom of the bowl, where it feeds into the main jet passage. Not a lot of depth for a thread insert either. An 1/8" NPT plug is pretty close and with the taper might have a chance of sealing up.
	1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45

Les Kerf Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 08 May 2020 Location: Idaho Points: 1510	Post Options Post Reply Quote Les Kerf Report Post Thanks(0) Quote Reply Posted: 11 hours 16 minutes ago at 10:41am
	Maybe try tapping the hole to 10 mm, then seal the threads with non-hardening Permatex Aviation #2 gasket sealer?