Stan Bradbury's Speedway Training Notes

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CARBURETORS

The Dell Orto PHF carb (stamped on the side of the carb) is now obsolete and many of its parts unobtainable. Some parts are interchangeable with the later PHBE but are expensive. Some of these parts can be made by any competent machinist. Inquire if in doubt. Main and needle jets for all Dell Orto and Amal carbs, can be made by drilling out the smaller orifices in the equivalent gasoline jets which are usually obtainable. These gasoline jets are drilled out using either Wire number drills or Metric sized drills. Metric jet number correspond to the metric drill size. Amal jet sizes are based on flow rates at a specific head and require a conversion chart to obtain the Number drill approximate equivalent sizes. The jet sizes recommended by European sources are generally too lean for Canadian conditions due possibly to different sources of methanol, atmospheric or altitude conditions etc. This could lead to overheating causing seizures, plug failures, melted pistons, damaged exhaust valves etc. I would strongly recommend increasing main jet settings above those recommended by Jawa, Godden, Weslake etc. In general, jets should be slightly increased in size when switching from short tracks to long tracks.

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