This maybe useful to anyone having slow running problems with a J60 engine.
We cleaned the carburettor and jets using compressed air, as well as carb cleaner, then we found a jet with a damaged thread on top of the venturi tube (solex 190). The jet would not seat properly.
After removing and cleaning the idle mixture screws, by chance I injected compressed air into the mixture screw holes only to find that there were air leaks between the 2 halves of the carburettor body accompanied by bubbling carb cleaner at the joint.
The carburettor is in two halves with a gasket between. The 5 socket head screws holding the 2 parts of the carburettor together were all loose, even after tightening there were still slight leaks, so presumably the carburetor joints were warped. The fix was a very thin coat of Hylomar.
These issues, including a dirty carburettor will have contributed to poor running, and the joint leak may never have been found were it not by chance. Worth a check if you cannot get the vehicle to idle properly.
Diana