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+--- Thread: Zenith 22 FZ Slow Running Tube Lock Screw (/showthread.php?tid=8830)
Zenith 22 FZ Slow Running Tube Lock Screw - Steve Jones - 22-08-2023
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
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Howard Wright - 22-08-2023
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
RE: Zenith 22 FZ Slow Running Tube Lock Screw - John Mason - 22-08-2023
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
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Steve Jones - 22-08-2023
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
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Ruairidh Dunford - 22-08-2023
M4 is correct, the threads on the rest of the carb are also metric.
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Dave Mann - 22-08-2023
The threads on the 22 FZ and 22FZB are metric. If you fit a replacement retaining screw make sure it is not too long as it can jack the side of the housing off particularly on the 22 FZB like this
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Steve Jones - 23-08-2023
Many thanks Howard, Ruairidh and Dave. M4 it is and Dave's warning noted. Problem solved.
Steve
RE: Zenith 22 FZ Slow Running Tube Lock Screw - Ruairidh Dunford - 23-08-2023
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"