Carburettor
February 2004:
the carburettor choke control was well and truly seized and the throttle spindle flopped around an amazing amount.
Equally amazing - all the wear was on the spindle - a new spindle from Burlen has solved the problem.
the carburettor was reassembled and put back on the manifold. A replacement choke assembly was located and fitted; so the external return spring is no longer needed.
These are the two jets - the main jet is physically smaller than the compensating jet.
I prefer rich running so the main jet was opened up slightly: these settings are fine for the winter.
Main (smaller) jet is 75 (standard 72)
Pilot Jet is 60 (standard 60)
Compensating (larger) jet is 55 (standard 55)
Standard choke size of 19mm
see the ATDC magazine August 2005 for all the jet sizes for these Zenith carbs.
November 2006:
I acquired a 21mm choke carburettor as fitted to the 1936 Lichfield and Sherborne models.
Main (smaller) jet is 85 (standard 82)
Pilot Jet is 60 (standard 60)
Compensating (larger) jet is 55 (standard 50)
This slightly later carburettor looks identical but has several improvements and immediately set up well, with no hesitation through the range of speed and power
November 2007:
This 21mm carburettor need no adjustments when I fitted the aluminium head