Solex dual barrel carburetors first appeared in 1960 on the Super 90 and continued on the SCs and all 912s through 1969. (Click on image to get a larger version you can download)
Early 1960 Solexes:
• Distinguished by small brass breather tube on top plate
• Dependent idling carburetor, if the main jets are changed it affects the idling circuit.
• Some say frustrating carbs to tune and get to pull smoothly through the rev range.
• Gray pot metal with silver plated hardware
• Sometime in mid-1961 with possible serial numbers starting above 6,000
• Independent idling system, possible now to change main jet without changing anything else.
• Larger diameter and shorter brass vent tube in top cover
Difference Between Solid and Split Shaft Solex 40 PII Carburetors:
In order to meet stricter emissions standards in 1968, Solex made several modifications to the solid shaft 40 PII.
• Bronze bushings were installed solving the wear issue.
• Split shaft system allowed for throttle valves to be balanced separately. Solid shafts had a nasty habit of twisting over time leaving one throat to draw more air than the other.
• Addition of two more holes just above the closed throttle plate to smooth out the transition from the idle circuit to the main jet circuit.
• Serial numbers in 1968 ran 8,xxx,xxx and in 1969 9,xxx,xxx
• Late 1967 for '68 model year, switch to gold plating and gold hardware
Stock jet set ups are as follows: Solid Shaft Split Shaft
Main jets 115 or 120 122.5 or 125
Air correction jets 180 180
Idle metering jets 55 57.5
Idle air bleed (correction) jets 1.8 1.1
Accelerating pump jets 50 40