The MGA With An Attitude
NO FUEL FEED - Engine Does Not Run - CB-111

At 11:12 AM 3/13/2007 -0600, Roy Lewis wrote:
"Cannot get car to run. Spraying a little ether in the carbs will allow it to run 5-10 seconds".

That's simple. Fuel is not getting into the main jets, or maybe just not enough fuel.

Be aware that there is no automatic choke on the MGA. It has a manual choke. When properly tuned the choke must be used to get it to run on cold start. Pull choke full out and crank to start, along with a little step on the throttle. There is no accelerator pump in an SU carburetor, so it doesn't do anything to repeatedly pump the gas pedal. Once it starts you can push the choke in part way. As it warms up you can push it in farther. After a minute or two of running it will not need choke at all (except in very cold weather for a little longer).

Once running after cold start you can determine how much choke it needs by the way it runs. Too much choke and it will "gallop", which is running rough in cyclical cycles changing speed a couple of times per second (sounds like a horse galloping). If so, push the choke in a little. Too little choke and it will idle rough or stall, and it may hesitate badly with attempt to accelerate. If so, pull the choke out a little. With correct amount of choke it should run smoothly at a fast idle.

If the car had been laid up for a long time any of the throttle or choke parts could be sticking, either open or closed. If the carbs were disassembled the choke linkage may not have been properly adjusted after reassembly. See CB-102 for choke adjustment.

You can manually pull or lift up the choke levers where they are linked together down low between the carburetors at the cable attachment point. When you actuate the choke levers they move in teeter-totter arrangement, pulling down on the main fuel jet at bottom center of the carburetor body to enrich fuel mixture. There should be a tension spring on the short end of the choke arm. When released, the jets should move back up against the mixture adjustment nut. If they stick in the lowered position, push the jet up with your finger to snap back against the mixture-adjusting nut. Cycle the choke a number of times to see if it will free up and move both ways without intervention from below. If it continues to stick you need to disassemble the main jet parts to fix the sliding seals.

If the manual choke is working, and being used properly, and it still doesn't start, check for spark first, then look for obstructed fuel flow. Disconnect the fuel flex line from body to carbs, hold in a catch vessel, switch on ignition momentarily, and check for fuel flow. You should get a veritable gusher, at least one pint per minute. If not, look for obstruction farther back down the fuel line, smashed steel pipe, clogged filter in the fuel pump, an air leak in the line between tank and pump, or clogged pickup tube in the tank.

If it has good fuel feed at the flex hose, then check for fuel in the float chambers. Switch on to pump fuel into the carbs, switch off, then remove the top(s) of the float chamber(s). If there is no fuel inside, the clog is at the inlet port in the float cover. There should be a thimble size screen in the inlet port at the hose connection banjo bolt. Check and clean the screen if necessary, or clean out the port leading to the float shut-off valve.

If there is no fuel in the float bowl, the float valve might be stuck shut or clogged. Push out the hinge pin to remove valve arm, pull the movable plunger pin out of the valve, blow air through to clean or verify free flow, and reassemble. When successful, the bowl will fill with fuel when pump is switched on. While you have the cover off, lift out float and clean out the float chamber.

It fuel is spilling out from the float cover vent pipe, then the float valve is not closing. Remove float cover and clean or replace the float valve.

If fuel is coming out of the main jet like a geyser, but no fuel comes out of the float cover vent pipe, that means the float cover vent is plugged causing pressure in the float chamber. If you remove the float cover you might find very little fuel in the float chamber because air cannot get out with the cover in place. Find the clog in the vent pipe or in the banjo bolt or seal washer below the banjo fitting.

If there is fuel in the float bowl, and it still doesn't run, the clog is further on. There is a small hole in bottom of float chamber where fuel feeds through the bowl-mounting arm into the carburetor body. It attaches to the carb body with a banjo bolt and a pair of rubber grommets. Fuel must pass through the banjo bolt to get into the carb body. If the rubber grommets are deteriorated they can swell and shift to obstruct flow from the float bowl to the banjo bolt. In that case you need to replace the rubber grommets.

The last fuel passage is inside the throttle body going to the main jet. See CB-106 for fixing drippy carbs. Here the main jet has two seals above and below a hole passing through the side of the jet to allow fuel to go inside where it can flow out the top into the carb throat to mix with air. These seals are commonly the source of a fuel leak out the bottom, not generally causing any obstruction to flow. It may be possible to have a clog at this location, but very unlikely to affect both carbs the same.

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