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MG MGB Technical - Normal fuel flow?

Just finished installing a "new" head (remanufactured with unleaded valves, skimmed,etc) to replace cracked one. Car started right up, idles & runs smoothly. Timing on. New plugs. However no power, even less than with cracked head. Have two new see through fuel filters. When I turn on the ignition (without starting the car) I hear the pump (new, electronic) click a few times but I see no fuel in the filters. When I start the car and give it some throttle I see very little fuel coming into the fuel filter in the engine compartment. Sort of like a dribble. Is this normal? If not, could this be my lack of power? Thanks.
David Hawkins

David. Your fuel filter should be at least half full with the fuel pump running. It sounds like you have a fuel delivery problem. Good information in the archives about how to check this out, blow lines clear, problems with pick up tube in the tank, etc. Some items, such as pick up tube, vary with year. RB cars use a combined sender unit and fuel pick up tube which is easily replaceable. With earlier cars it is built into the tank. A vacuum/fuel pressure gauge can be used for part of your trouble shooting. You should have 1 psi fuel pressure to the carbs. With a new pump, this should be 1.5 to 1.75 psi for SU carbs. A Weber DGV series can use 3.0 to 3.5 psi, but also seems to run well with the lower pressure SU pump. Bad connections at the tank or pump will allow air to get into the system, causing a problem similar to what you describe. You can check the pump and lines forward by attaching a line to the pump intake and running it into a gallon can of gasoline and see if it pumps correctly then. If so, you probably have a problem in the line going to the tank, the pick up or the tank itself. If it does not pump correctly, you may also have a problem in the line going forward to the carbs. Also check our theads on the fuel tank and rust and sediment related problems. Les
Les Bengtson

Dave,
The flow spec I have been given is 1 pint a minute at the carbs. Disconnect the fuel line at the carbs and turn the ignition to on. I used a beer bottle and waited 30 sec. It should be about 2/3 full. An assistant is useful but not required. Are you using an SU electronic fuel pump or an aftermarket style from purolator or similar. If it is the aftermarket style, check the piping to the pump. They work ok (I prefer SU style) but are sensitive to hose routing (so are SUs but most of us stick to standard hose routing) The pump suction needs to be low at least as low as the hole the SU fit in. A few are mounted using the holes that the SU pump bracket uses one of which is so high that the car will run if it is only 2/3 or more full. A quick check is to fill it up (the gas tank) and see if it runs better the downside is if the pump needs replacing. You got a full tank forcing gas out.

A few ??? What year car? What type of CARBs? If SU Carbs, heatshield installed? Does the pump keep clicking?

ATB,
Tom
Tom

Thanks for all your feedback. Will do the testing suggested.

In response to Tom's Qs: Its a '73 Roadster with Weber DGV. The pump is an electronic one I got from Brit-Tek that looks exactly like the original SU but I don't remember if its an SU and don't have the catalogue in front of me to check. An no, after a few clicks it stops and does not keep clicking.
David Hawkins

This thread was discussed between 06/09/2001 and 07/09/2001

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.