WEEKEND WORKSHOP
How to save some cash by overhauling Britain’s most popular classic carburettors
Save £240 in four hours
NIGEL'S JOB CARD OVERHAUL STROMBERG AND SU CARBURETTORS
Covering several installations, today Nigel is overhauling carburettors fitted to many British classics for over 50 years. SU and Stromberg carbs both meter fuel supply via a single jet and tapered needle, which is controlled by a dashpot responding to inlet manifold vacuum, known as a ‘Constant Depression’ design. The basic operating principles are straightforward. We will tackle both types, stripping, cleaning and overhauling them, ready for years more reliable service.
START DAY 1
REMOVAL & CLEANING
Filters and linkages
Remove carbs by disconnecting fuel lines and unbolting air filters. Undo the choke and throttle linkages and remove any return springs. Note how cables and springs connect for reassembly later.
Remove the carbs
Undo nuts securing the carbs’ flanges to the inlet manifold. Small versions have two-stud mountings, while larger SUs and Strombergs have four.
Remove SU jet
Disconnect the enrichment (choke) lever from the side of the jet assembly and undo the jet’s fuel line from the bottom of the float chamber. Pull the jet from its holder. This is a later Waxstat jet.
Stromberg dashpot
Remove the damper rod and undo the four screws retaining the dashpot cover. Lift the spring and piston/diaphragm/needle assembly from the carb body. Put these parts carefully to one side.
Metering needle
The metering needle is held by a single screw in the side of the dashpot’s piston. Loosen the screw and pull out the needle. This is a later sprung bias type needle; earlier versions have a solid shank.
Solvent clean
Clean the carburettor components thoroughly with solvent. Dry the cleaned parts, blowing through jets etc to remove all specks of dirt. If available, an ultrasonic cleaning bath is ideal.
SOLVENT SAFETY: When using solvents, wear suitable gloves, mask and eye protection, away from sources of ignition.
First clean
Most carburettors get covered in oily grime under the bonnet. Start by cleaning the exterior and linkages using a degreaser and paintbrush, then hose down. Dry the carbs thoroughly.
STRIPDOWNAND DEEP CLEAN
Remove SU dashpot
Start by removing the dashpot. Unscrew the damper rod, then the two or three screws securing the dashpot itself. Lift away the dashpot, spring and piston, taking care not to damage the needle.
SU float chamber
The SU float chamber bolts to the side of the m
