Joined: Aug 2017 Posts: 1,474 Threads: 26
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Location: North Yorkshire
A friend has lost, on the road, the locking screw that holds the slow running tube in place on his updraft bronze Zenith and he's trying to find out what thread it has so he can source a replacement. Mine is M4 but I don't know if it's been messed about with in the past. The locking screw on mine is certainly a brass original and metric threads turn up on Zenith carbs sometimes so, maybe M4 is correct. If it isn't, it's certainly something very close to M4. 2BA has been suggested but that's too big.
Anybody got a definitive answer?
Steve
Joined: May 2018 Posts: 2,121 Threads: 111
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Location: Llandrindod Wells
Car type: 29 Special, 30 RK, 28 C Cab
Hi Steve
I’ve just checked my spare FZ22 bronze carb and the slow running lock screw is definitely M4. Unfortunately it’s not an original round head brass screw but a pan head stainless screw. However I thought Zenith were pretty exclusively metric in the late twenties?
Cheers
Howard
Joined: Dec 2017 Posts: 1,160 Threads: 68
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
On what has been said about M4 metric thread I would gently try a M4 screw into the thread and see if I fits,
John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
Joined: Aug 2017 Posts: 1,474 Threads: 26
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22-08-2023, 04:55 PM
(This post was last modified: 22-08-2023, 05:00 PM by Steve Jones.)
It does - on mine! And on Howard's spare (thank you). What I'm trying to determine is what's the original thread, not what might fit today.
Steve
Joined: Mar 2015 Posts: 5,469 Threads: 231
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Location: Scotchland
M4 is correct, the threads on the rest of the carb are also metric.
Joined: Aug 2017 Posts: 1,474 Threads: 26
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Location: North Yorkshire
23-08-2023, 01:01 PM
(This post was last modified: 23-08-2023, 01:03 PM by Steve Jones.)
Many thanks Howard, Ruairidh and Dave. M4 it is and Dave's warning noted. Problem solved.
Steve
Joined: Mar 2015 Posts: 5,469 Threads: 231
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Location: Scotchland
From Stuart Joseph:
"Carburettors bought in by Austin from Zenith had metric threads e.g the float chamber on the 26va is held on by two 7mm bolts.
However the Zenith carbs supplied to Fords had BSF threads. The float chamber fitted to downdraft Ford carbs are almost identical to that of the 26va except it is held in place by 5/16 BSF bolts. I have had to Helicoil many float chambers to 7mm to accommodate the bolts sold by The Seven Workshop.
Thanks in anticipation
Best regards, Stuart"
