MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - SU Carburetor leak diagnosis??

My forward SU carb developed a sudden 'pissing' leak from the float bowl overflow today. The engine ran rough and finally lost idle when throttled down. The leak stops when the ignition is switched off...and restarts immediately upon introduction of power from the ignition switch to the fuel pump. Any ideas on what the cause may be? Is this necessarily indicative of a need for a complete carburetor rebuild? Where does anyone suggest starting to diagnose the cause in this repair? Suggestions, comments, common experience is helpful. Thanks member and friends.
Steve Lofaro
Stephen Lofaro

If it is a leak that just started all of a sudden, and is a large leak from the overflow pipe, it sounds like grit in the inlet valve of the SU bowl.
Remove the bowl cover. Blow air through the valve to clear it. Remove the float and shake it to check that it does not have fuel inside it and has sunk.
Reassemble.
Do you have a fuel filter? Cars with 50 year old fuel tanks must have a filter. A plastic filter with a paper element will do the job. Fit it in the line anywhere before the line divides for the two SU's. Note the filters normally have a fuel direction arrow.

Mick
Mick Anderson

Hi Stephen Recurring flooding likely means that the needle and seat in the float chamber isnt working properly. Often times the needle valve problems are caused by rust in the gas tank or fuel lines getting pumped up into the carb float chambers. If you have a severe rust problem, cleaning out the float bowls, and changing the needle valves likely wont cure the problem. You should probably remove both float bowl covers, remove both floats, and check the float bowls for rust or sediment. If there is lots of rust or sediment, then the gas tank and fuel lines need to be thoroughly cleaned or replaced. If there is only a bit of rust or sediment then you might get away with installing just a high quality fuel filter and / or a set of grose jets, to replace the standard float chamber needles and seats. Good luck, Glenn
Glenn

If you have an original fuel pump, there's no need to fit a separate fuel filter - there's one built into the bottom of the pump, and two more at the carbs (inside the banjo where the fuel line attaches to each carb). While those at the carb have a fairly coarse mesh, the fuel pump one is a very fine nylon gauze, and is quite adequate to stop anything coming from the tank. If your fuel lines are so rusty or rotten inside as to be creating a problem downstream of the pump, it's time to replace them.

It sounds like the valve is stuck, as the others say, or maybe the float has become a sink(!). Clean all the filters while you are at it. Seeing the charcteristic of the crud in the float chambers may indicate where it's coming from. If the float is duff, it can be fixed with a dab of solder if it has a hole.
dominic clancy

Easily diagnosed as a leaky needle valve. It could be gummed up, or it's seat loosened up, or dirt (rust)or the float with a hole, or the lever arm being bent out of shape and jammed. If it is gummed up, it can sometimes be remedied by a sharp "rap" with the wrong end of a screwdriver to the bowl cover. This helped me a couple of times. All the others only requires removing the top and cleaning.

Chuck
Chuck Schaefer

It is also very likely a float that has a hole in it. This has happened twice to me. Take them out of the bowls, dry them off and give them a shake. If you can hear the fuel inside then you've found your problem. Don't bother with attempting to repair the hole, just buy new.

j
JohnB

JohnB

Holes in floats repair very easily. When one of mine became perforated I just drilled a small second hole to drain out all the fuel. Left it to dry out and then soldered both holes. Been working fine for the last few years. It was standard practice before the modern throw away society.

Steve
Steve Gyles

This thread was discussed between 11/03/2007 and 12/03/2007

MG MGA index

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