Carburettor Jet sizes 1926/7 12/4

[bsa]

Hello Just wondering if anyone has details of original jet sizes for the Zenith carburettor fitted to 1926 and 1927 heavy 12/4. I have a slight issue with an occasional missfire. Also feel its a bit down on power compared to my other 12/4's. I have checked the valve timing and cylinder compressions ( all 90psi) also stripped the carb and cleaned. Still have this issue and the plugs are rather black....especially if I compare to my other 12's where the plugs are a nice tan colour. Any suggestions welcome. The engine was rebuilt not many miles back and I have the receipts to prove and it runs very quiet and smooth. Dont know what I can do next.....many thanks for any suggestions. Thanks Nick

[Media-Moderator]

Hi Nick.
It may be worth having a chat with Tony Smallbone - his number is in the magazine.