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An explanation of the two types of slide for Dellorto PHF and PHM carburettors

PHF/PHM slides are split into two categories, early and late. Early carbs need an early type slide, later carbs can use either. The way to tell which type of carb you have is to remove the top and slide and look inside at the base where the slide sits. Early carbs have a round base

Later carbs have a round base but the top and bottom is cropped to give  flats on the side like this.

The slides therefore differ in the size of their idle speed ramp, Early slides have a small ramp, later slides have a larger ramp that is given clearance by the cut outs in the base of the later carb

like this

You can see here the slide on the right has a larger ramp and will only fit a later carb.

Early type slides are becoming hard to find now as production stopped some time ago ..Despite what Dellorto say it is not practical to adapt the new slides to fit old bodies because you need to machine most of the Tick over ramp down which gives you virtually no adjustment with tick over  after a few months.

The numbers on the base of the slide refer to the slide cutout and Pump ramp so for example a 60/1 has a 60 (6mm) cutaway , the smaller the cutaway the faster the airflow over the atomiser and the richer the mixture, and a No.1 (/1)  Accelerator pump ramp..The lower the number the lower the ramp starts for the pump in the groove on the slide so the earlier the pump operates.