What spark plug should I use?
The vast majority of seagulls use an 18 mm plug. It must be a short reach, to avoid damaging the piston. The most common used and found), are NGK A6, or the D 16. The old 8 Com is not available now, except old stock.
There is also a Bosch version of the D16, the Bosch M 10 A C but it is not generally found.
Exceptions to the above!
All Q.B. seagulls, the Kingfisher, Osprey and Curlew :-
use a 14mm, either, Champion N4 or RN4.
or NGK B7ES or BR7ES.
(The ‘R’ denotes a resistor plug.)
The Model 125 and 170(the ones with cowlings):-