The del orto carbs, the needle end perishes with age, it's imperative to renew both the needle and seat, the new kit includes a washer that fits behind seat, this must be fitted also. After fitting do a blow test, blow down fuel tube into carb, air should pass into carb, invert carb, do same again, this time you should not be able to blow into carb, if you can, then its time to maybe tweek the float, or its more likely the float is interfering with the side of the float bowl. With patience the carb can be returned to a usable condition. The first time I did this test, I had some residual of fuel in the carb, which when the carb was inverted, I injested, to get rid of the taste, i went to my local pub and asked for a double scotch, the landlord replied, 'are you celibrating', I said no i've just done my first blow test, he said thats usually a time for celibration, I replied, I'm just trying to get rid of the taste.