75 HP Bristol engine.

[Geoff Dowdle]

Lewis,
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 ......

1. 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.

2. 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 carby top
. Note machining of the carby tops can be different different for different
Solex applications.

3. 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

4. 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.

5 Although not directly related to Carby 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 Malloy twin point unit, thats is fully adjustable.
There is no point in converting your Lucas to electronic operation while the
advance curve is no where near correct. You must have a TDC make on either
the flywheel or fcrankshaft fan belt pulley to operate a timing light .

6 Unless you do most or all of the above you will never get a 6 cylinder
Bristol running nicely.

Must go, Good Luck
Geoff Dowdle
I