Here are some tips on tuning Solex carb by Geoff Dowdle

  1. It is quite a lengthly process to try and correct 50 plus years of abuse on those old Solex. The most important things to look for before you start tuning as per the manual is ……
  2. Are the 3 carbs the same, especially the throttle bases, make sure they all have the same number of progression holes ie 2 for 401 – 405 , 3 for 406 & D2. All faces must be flat including the adapter the carbs bolt to.
  3. Float levels MUST be at 16mm down from the top of the main body when the engine is idling, this can only be measured by making up an external plastic sight tube attached to a spare main jet holder. The levels are adjusted by shimming the needle & seat unit in the carb top. Note machining of the carb tops can be different for different Solex applications.
  4. Make sure the jetting is correct, ALL JETS & Emulsion tubes. Check the diameters with various size metric drills. Many original jets have been incresed in size over the years by drilling out. As a rule you should need slightly leaner jets than STD as the quality of modern petrol is so much better than the very poor petrol of the late 40’s and early 50’s.
  5. I usually replace the nice brass AMAL throttle rod ball joint ends (usually badly worn) with new ones to allow the throttle butterfly’s to go back evenly on the adjustment screws.
  6. Although not directly related to Carb tuning, valve clearance must be correct, distributor MUST be in good working order, advancing correctly. Very few Lucas distributors work well even when new, they were poorly made. (BAC used Delco Remy twin point for all the BS engines). I usually replace the Lucas with a modified Mallory twin point unit, that is fully adjustable. There is no point in converting your Lucas to electronic operation while the advance curve is nowhere near correct. You must have a TDC mark on either the flywheel or crankshaft fan belt pulley to operate a timing light.
  7. Unless you do most or all of the above you will never get a 6 cylinder Bristol running nicely.

Geoff Dowdle in 2008