AJS & Matchless Owners Club

Hi -
I've measured across manifold bore to arrive at 1" bore but I am scratching my head as I have a 1958 600cc motor which for the year should be 1 1/16" Perhaps I've got an earlier 1956 motor manifold....I know there is not much in it but does anyone have any knowledge of fitting slightly oversized carbs on m/cycles?
The earlier 1956 models with the 1" inlet bore had a slightly larger 300 main jet, whereas the later year (my engine model 1958) had a smaller 280 main jet. All other fitted parts are very similar 280 main jet (without air filter) 3 1/2 throttle slide - 30 pilot jet -106 needle and sited central needle position...
So which inlet bore sized carb do I go for? (I did notice on the carb manifold that the bores on the cylinder side were oval so difficult to determine any accurate measurement....
Regards
Pete

Having a larger carburetor diameter than the inlet manifold, even 1/16", creates an obstruction which disturbs the airflow.
While this may be minor it can cause idle problems etc.

you say its a 58 model 30 but its made in 57 so it would have a 376/58 with a 1 inch bore and a 260 main jet a 30 pilot jet ans a 106 needle jet and a number 4 slide, hope this helps.