Autumn is the right time to give your classic car a proper going-over before the cold weather sets in. Whether you are planning to store the car through winter or intend to keep driving it, getting the fuel system in good shape now will save you problems in spring — and possibly prevent a breakdown on a cold, wet morning.
Check the Carburettors
Dashpots and Oil
If you have not changed the dashpot oil since the last service, do it now. SU carburettors rely on a hydraulic damper to control mixture enrichment under acceleration. Old or contaminated oil causes sluggish response. Drain the dashpot by removing the damper cap and tipping the unit, then refill with the correct grade — typically SAE 20 for most applications, though some recommend light engine oil. Overfilling causes flat spots; underfilling causes hesitation.
Float Chambers
Drain the float chambers and inspect for sediment or varnish deposits from old fuel. Ethanol-blend fuels degrade rubber seals over time and can leave a residue that blocks jets. If the car has been sitting, it is worth removing the float chamber tops to check the needle and seat for wear — a worn seat is the most common cause of flooding and an over-rich mixture.
Throttle Spindles
Worn throttle spindles allow air leaks that upset mixture and cause rough idling. With the engine idling, spray a small amount of carburettor cleaner around each spindle. A change in idle speed indicates air is being drawn in past a worn spindle — a rebuild or replacement is needed.
Check the Fuel Pump
Cold weather can tip a marginal pump into failure. Test yours now by listening to the click rate at start-up. A pump that clicks slowly or unevenly, or that requires several cranking attempts before the engine catches, should be rebuilt before winter. Rubber diaphragms that have been softened by modern fuel blends are particularly susceptible to cold-related failure.
If you are storing the car, run the engine until it reaches temperature, then switch off and drain the float chambers. Fuel left in carburettors over winter turns to varnish and can block jets and needle valves.
If You Are Storing the Car
- Use a fuel stabiliser if leaving petrol in the tank, or drain completely
- Drain float chambers with the engine warm
- Fit a fuel system moisture absorber if storing in a damp location
- Run the car every three to four weeks if possible, long enough to reach full operating temperature
Getting Work Done Before Winter
If your carburettors or fuel pump are due for professional attention, now is the ideal time — before the autumn rush. Our carburettor and pump refurbishment service covers full strip, ultrasonic clean and reassembly with new wear components, and we turn work around promptly. All refurbished units carry a 2-year guarantee.