How to find a running fault
Q I can’t get my 1964 Victor FB to run properly. It starts easily and revs fine in neutral, but it has a lumpy tickover when hot and hesitates badly on acceleration. It cruises well at 50-60mph, but when you put your foot down it trips over another flat-spot. It sometimes backfires, too. The coil and plugs are new. I’ve rebuilt the the carburettor and distributor. The ignition timing and mixture are spot-on. Ideas welcome. Peter Newbrook, Stoke-on-trent A When tackling a persistent mystery, it’s best to restart with the most basic things, going on from there and leaving no stone unturned. Make a list and tick things off as you go.
Make sure the spark plug gaps are set to 0.6mm. Gap the points to 0.4mm when their heel is on the lobe of the cam and check the cam for wear. Follow the advice in your manual to set the ignition timing with a strobe, which eliminates inaccuracies caused by distributor drive wear. Make sure the distributor spindle and baseplate have no slop and that, with the points held open, the rotor springs back all the way when twisted against its advance springs. Don’t confuse ‘all the way’ with all the way plus backlash in the drive gears – be sensitive.
Change the condenser.
Suck on the vacuum advance and place your tongue over the end of the tube to make sure it holds vacuum. Test-drive the car with a wire directly from battery positive to the coil’s + terminal and a fresh wire from the – terminal to the distributor. A point of high resistance in the wiring may cause a weak spark.
Eliminate any slop in the throttle linkage. This won’t cause a flat-spot, but will introduce a delay when pressing the pedal. Check the carburettor float level is correct and that the needle valve is screwed tightly home and doesn’t leak when closed. Blow out all the jets and make sure the accelerator pump, if fitted, delivers a good squirt even when the throttle is opened slowly and slightly. Make sure the gaskets between the manifold and carburettor are sound, and the throttle spindle is not rattling around in its bushes.
If a brake servo’s fitted, disconnect the manifold pipe, plug the stub and go for a testdrive (noting heavy brakes!).
Next, replace all the fuel hose on the car, from the tank to the carburettor. Replace the metal pipe that runs under the car, which may be perforated, kinked or silted-up. Replace disposable filters and clean any gauze filters (tank pickup, fuel pump, carburettor inlet). Clean out the tank if it’s crusted with black ‘varnish’ and/or rust. Check the fuel pump valves. It should be impossible to blow back through the pump. Check the diaphragm. Test the pump pressure (4-5psi) with a gauge and alter the gasket thickness to adjust.
Set the valve clearances (cold) and perform a compression test (hot). Compare to the figures in your manual. If the compression varies more than around 1015psi between cylinders, suspect faults in the low ones. Put a few squirts of oil down the plug holes and repeat. If the compressions improve a little, all’s fine. If they improve a lot, this points to bore/ring wear. If the compressions remain stubbornly low, the valves are leaking.
Last but by no means least, check your camshaft timing. You will have to remove the timing chest from the engine to check the marks on the sprockets or gears. It is not unusual to find it’s a tooth-or-two awry.