The Garage – Sudden Stops by Mike Owen of Owen Automotive
Unless you are a skilled mechanic, nothing will chill your heart like your LBC quitting in the middle of nowhere… The engine cuts dead, it turns but won’t start. There are no knocks or rattles and the temperature and oil pressure was fine.
The problems generally arise from either the fuel system or the ignition system.
Fuel system – One definite possibility is there is no fuel supply to the carburetors. If out of fuel or the pump has quit, there would be surges of power before the silence. Most cars have electric fuel pumps which are generally reliable provided the car is operated regularly. If not, the points often corrode affecting the spark. Gentle taps on the fuel pump with a wooden mallet often will set things right. Try turning the key on and off several times to see if it corrects. Otherwise clean or replace the points from the emergency spares kit. Austin Healeys will sometimes run dry if the fuel tank is less than one-half full when driving uphill. Check that all wiring is clean and tight.
Fuel filters can clog up quickly even though they appear clear. This can be a problem when driving uphill. Turning the key on and off might help. It is a good idea to install a new filter when doing annual maintenance.
Most gas caps are vented with a vent hole to prevent a vapour lock which is like running out of fuel. Some later cars – MGBs, TR6s, and Midgets – have a carbon canister instead of the vented cap. This is not just part of the pollution controls and replacing it with a bolt will close off the vent.
A sticking float needle will cause flooding and an overflow of the excess fuel. Try tapping the top of the bowl with a wooden mallet. Otherwise, remove the cap and clean out the needle and needle assembly. The original brass floats are prone to leaking and filling with fuel. The after-market synthetic black-colored floats seem to work well as replacements. Occasionally, a carburetor piston can stick. Make sure they are able to move freely in the chambers.
Another problem can be after-market fuel pumps that put out more pressure that is suitable. The SU pumps are low-pressure pumps and put out about three pounds.
Another potential problem for MGBs is original fuel hoses that become brittle and disintegrate.
If old gas overwinters in the carburetors, there can be combustion problems. It is a good idea to install a switch in the ground wire to turn off the fuel pump and run the car until the carburetors are out of fuel. This can also serve as an anti-theft device as the car will only go for about a block before it quits…
Ignition system – The points in electric distributors are also prone to corrosion from sitting around. Either clean or replace them and ensure the gap is correct. Add a little “point” grease to the rubbing block of the points set where it connects with distributor cam. Use a grease with a high melting point such a wheel bearing grease. Also, watch for a tight fit on the pivot pin which can jam when it heats up. Make checking the points a regular part of maintenance routines.
Lucas condensers have been unreliable – a better make is the Standard Ignition Condenser available from JB Precision Engines in Victoria.
Poor quality rotors have been in circulation for many years – often as spares in toolboxes. Do not use the after-market ones with a brass rivet. Red ones have been best for early cars, blue for later ones. A faulty rotor will stop a car dead – replace it.
Check for a worn ground wire for the points which will stop the car. If the LT wire from the terminal bush is worn, be sure to replace it with a correct part as it acts like a fuse in the event of a short.
The distributor cap can be a source of trouble. The carbon brush and spring that acts as the centre contact can pop out or stick in the up position. To be sure it is making a proper contact with the rotor, examine the centre to see if it has a polished centre rather than a black burn. Look as well to see if there is a jagged line etched on the inside of the cap that would indicate a short between two terminals. A cracked cap will probably misfire before it fails. Replace the cap.
Pertronix ignitions are reliable. Be sure to connect the LT wires to the coil correctly. If accidentally reversed, the unit will burn out. Test for the live wire with a test light if in doubt.
For the coil, wiggle the LT leads while the engine is running to see if the engine falters. There can be a poor connection or a wire break. If the car has a push-in connection for the HT wire to the coil, check to be sure the wire isn’t loose. Wind electrical tape around the cap and wire to secure them in place.
MGAs and TR3s use screw connectors on the ignition switch. The grub screw can loosen and fall out.
Battery leads must be clean and tight. If the terminal has a cut-off switch, ensure the knob is tight.
On MGBs, the heater control valve is above the distributor. If the heater is not used regularly, the rubber diaphragm can tear and drip antifreeze onto the distributor. Look for a stream of antifreeze under the car or steam.
Another serious failure is a generator or alternator that stops charging. The car will run for a time on battery voltage and when it is insufficient to operate the fuel pump, it will quit. Many cars have a dashboard red light that indicates when the battery is not being charged. It can be difficult to see on a bright day. Also, be aware that if the generator bushes wear out, the light will not work. To check the light, it should glow when the key is switched to start. It will go out when the rpms are greater than 1200. Some drivers prefer to switch to an alternator but a generator with good bushes does a good job.
Other Problems – Occasionally, there can be air leaks in the intake manifold resulting in a vacuum leak. Some models are fitted with hoses attached to the manifold that fall off and the frost plugs at the ends of the manifold can fail.
Hopefully one of the first of these fixes that you try at the roadside corrects the problem.