|The MGA With An Attitude
LACK of FUEL FLOW -- FU-107
If your engine quits, or doesn't start, the first move is to check the fuel gauge. No gas, no go.
If there is fuel in the tank, switch on the key and listen to see if the fuel pump is running. Original equipment type fuel pumps will click rapidly at first, then slow down and stop clicking as the carburetors fill and the fuel pressure comes up. It is acceptable for the fuel pump to click periodically when the engine is not running, maybe once every 10 to 30 seconds, although it doesn't have to. If the fuel pump doesn't click, check for electrical power at the pump with key on. No power is an electrical supply problem, generally a disconnected or broken wire, because there is no fuse for the fuel pump supply. If there is power at the pump, and the pump still doesn't click, you may need to clean the contact points in the cap end of the fuel pump, or find some other internal problem with the pump. See Electrical Tech for more information on the electric fuel pump.
If the fuel pump clicks more often than once in 10 seconds with engine off you should check for leaks. Look first for massive flow from the carburetor overflow tube(s) to the floor on the carburetor side of the engine which indicates a sticking float valve. For that, remove the float cover to clean (or replace) the float valve. Dripping from the bottom of a carburetor requires attention to repair the seals at the main fuel jet or at the base of the float chamber.
The fuel feed path runs along the right frame rail from back to front, then upward and across the heater shelf from right to left, then forward to the carburetors. Dribbling from any connector joint in the fuel feed path requires attention to repair the connector to stop the leak. Dribbling from any hose or metal fuel line requires replacement of the hose or pipe. Any fuel leaking from the bottom of the fuel tank may require repair (or replacement) of the tank.
If there are no leaks, but the fuel pump continues to run, disconnect the hose bringing fuel to the back of the rear carburetor. Be prepared to catch any discharged fuel. Switch on the key and check for fuel discharge. You should get a veritable gusher here, more than one pint per minute (about 10 gallons per hour). You only need a few seconds to check the flow, then kill the switch.
If there is plenty of fuel flow, reconnect the line and switch on again. The fuel pump should run momentarily then stop clicking. If it does stop clicking, but the engine still doesn't start, you might have a carburetor problem. Before you start fiddling with the carburetors, remember that "90% of all carburetor problems are electrical". That is to remind you to check to be sure you have spark for all of the spark plugs before going any further with the carburetors.
If you do have spark and fuel feed up to the carburetors, then remove both float covers to be sure there is fuel in the float chambers. If not, remove, inspect and clean the filter screen at the inlet port on the float cover. If no problem there, remove the float cover and inspect the float valve to be sure it is not sticking shut. The float pin should drop freely by gravity when the float is allowed to drop. Holding the float cover assembly upright, blow into the inlet port to assure passage of air. If no flow, clean the inlet port. When the float is lifted it should stop the air flow. If not, clean or replace the float valve. When lowering the float allows flow, and raising the float stops flow, all is well. Replace the float cover, reconnect fuel hoses, switch on the key, listen for ticking to stop, then try starting the engine again.
If you have spark and fuel in the float chambers, and it still doesn't run, or it starts but seems to run on two cylinders (check spark plug wire order first), then you might check the condition of the rubber grommets at the base of the float chambers. Deteriorated rubber grommets there may allow fuel to leak, or might clog the holes in the banjo bolt to stop fuel from getting to the main jet in the throttle body.
Going back to the flow check with the disconnected fuel hose. If you have no flow or only a small trickle of fuel from the hose feeding to the carburetors, then reconnect the hose and follow the lines back toward the fuel pump to find the problem. Disconnect the output line from the fuel pump, being prepared to catch a fuel spill, switch on the key for a few seconds only to check flow and switch off immediately. If there is ample flow here, then follow the fuel line forward to check for kinks or a smashed pipe or a clogged hose that would be restricting fuel flow. Replace any damaged pipe or hose as required.
If the pump runs but there is insufficient flow at the pump outlet, then disconnect the inlet line from the pump. Check first to see if fuel flows out of the line from the tank, which would verify a clear supply line (if the tank is more than half full). Cap the line temporarily if it does flow. If no flow immediately, and less than half tank of fuel, you can either apply a slight pressure to the tank filler pipe or apply a small vacuum to the feed pipe between tank and pump to see if the line is clear and will allow flow. If it does flow then cap the line temporarily (if necessary) and go on to inspect the fuel pump. If still no flow from the tank, check for a smashed or kinked metal line (or a clogged connector hose). Also disconnect the line from the tank and check again for free flow. If the tank port and/or internal pickup line are clogged, try running a wire through the port to clear any debris in the internal pickup line. Maybe also try a momentary burst of air pressure, but be sure the filler cap is open and stand well clear of the filler port. If the pickup port is then clear and will allow flow, reconnect the lines and try the pump again. If the tank port or pickup line was clogged, you may ultimately need to remove the tank for internal cleaning.
If the tank to pump line allows flow, but there is still no output from the pump, then you have a problem in the pump itself. First remove and check and clean the screen in the pump inlet port fitting, then reconnect the inlet line and try the pump again. If still no output from the pump, then connect a hose to the pump inlet port and blow into the hose or apply a very small pressure. This should give a flow through the pump. If no flow with very small pressure, then the pump head is clogged and will need to be opened for internal cleaning. If flow is allowed with small inlet pressure, but the pump still does not provide fuel flow when it runs, then the pump has a fractured diaphragm or broken pull rod and will need to be disassembled to replace the faulty part(s).
Some aftermarket fuel pumps do not have a filter screen at the inlet port. In this case the internal check valves could get impaired with some trash from the fuel tank so they do not seal and may allow reverse flow. Any fuel pump with no inlet screen should always be used in conjunction with an in-line fuel filter before the pump.
When you have output flow from the pump, reconnect the lines at the pump, disconnect the hose at the carburetor and check again for flow there. If no flow or limited flow at the front, then there must be a kink or clog in the line between the pump and carburetors. Inspect, repair or replace the lines as necessary, and check again. Hopefully you will find the problem much earlier.