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 MGB Technical - Lost power

Am intending to post on MGA, MGB and MGC sites. After much trouble shooting I got my car to start quickly, run smooth, runs cool and shut down quickly but it has lost most of the power it use to have. It will run smoothly up to red line without any problem, just no power. I did notice that when i put the lights on the engine rpm dropped. Thought that would be more of a battery/alternator problem. The battery does show a bit over 12 volts on a simple meter and the alternator is a new Bosch.

What has been done: Full tune up - new points, plugs, rotor, cap, condenser, new wire where the coil wire connects and on to the points, new plug wires, plugs, coil. Removed the distributor, cleaned and lubed it. Static timed it. Switched out all the components at one time another over the last few months. Rebuilt the carbs including new jets and needles. Put on a new fuel filter. Rechecked delivery before the bowls and it will fill a pint in about 20 seconds. Checked to make sure the fuel lines from the float bowl to the jets were not twisted or bent in anyway. Have the jets set at .07 below the bridge. Tried adjusting jets with no improvement, only backfires.

All plugs firing, I can disconnect the carb linkage and increase the engine rpm with either carb. Any and all suggestions are appreciated.
Randy Palsgrove

How's the compression?
Daniel Wong

Randy-
Hmmmm........ Which coil did you use? Which spark plug leads? Which spark plugs? Of course, it's probably something much more basic. Are you sure that your distributor advance mechanism is functioning? Pop the distributor cap off and suck on the vacuum tube to be sure that it's working.
Steve S.

Randy. First question, since you intent to post on the MGA, MGB and MGC BBS, is "what car are you referring to?".

Static timing is a method of getting the car started after a tune up. It may work well if the distributor is new, but does not work well when the dizzy has a few miles on it. Dynamic timing is the key. As distributors get old, the springs wear and loose tension. This results in advanced timing at most rpms. Advanced timing leads to engine pinging/pinking. What is your dynamic timing and how does it compare with the factory specified curve for your distributor?

As it stands, you might have either an ignition problem or a fuel problem. But, until more information is available, it is hard to focus on what might be the exact problem. Les
Les Bengtson

Engine slowing when you turn the lights on is not a battery or alternator problem. Starting would reveal a battery problem, and if there were *no* slowing of the engine as the electrical load increased that might indicate an alternator problem. Some slowing is normal - the engine is now having to do more work since it is the alternator that is powering the lights. If your engine really is down on power then maybe it is so bad that it is having trouble even running the alt, but that is a symptom not a cause. A partial short on the (unfused) lights could be drawing much more current from the alt than it should. When is the voltage 'a bit over 12v'? When the engine is running at a fast idle and minimal electrical load you should see about 14v on, say, a brown at the fusebox. It should only show 12 po8int something voltas with the engine stopped or running with the ignition warning light on. Does the warning light operate as it should?
Paul Hunt

I'd go for the timing - check that you have 10 - 16 degrees BTDC at around 800 rpm and that you get a max of around 34 degrees.
Chris Betson

I should have supplied more information. The car is an MGC with the original straight 6. The car was a basket case and has been a real challenge most of the time. After several months things get a bit murky, especially if there are multiple problems at the same time.

In addition to previously mentioned information: I did all I have done because I thought the car would appreciate it and we would bond. Yes, it was running well. I would have to tap on the fuel bowls from time to time to get fuel going in both carbs or to stop fuel from flowing out the over flows. The alternator went bad and because the carbs needed attention I thought I would do the alternator, carbs and while at it a fresh tune up because I did not know when one was done last. These were the final touches to finish the restoration.

The exhaust is clear, probably too clear since it’s bout with backfiring. The clutch is in good shape. The vacuum is working, I can move the dist. plate by sucking on the vacuum tube and the rpm changes if I pull the tube. I have now checked timing both ways and it is to specs. When I turn off the engine the tach needle drops quickly, quickly enough to bounce off the peg. I remember Paul Hunt mentioning that it indicates a problem in the distributor I think.
Tonight I noticed the new solid state fuel pump making a lot more noise than normal. When I mention lost power. It runs nice and smooth without any power at any range or load, much like it is running on only half the cylinders which is what it may be doing which brings me to:

New and old puzzling things: I may again be dealing with several problems.

Presently clear fuel filter before the carbs will empty for a second or two and then squirt to about half full. This process it repeats. Apparently it is running only on the front three cylinders. I previously checked spark with a spark indicator which is placed between the plug and wire. It indicated spark to all the plugs. Pulled plugs and the back three were wet. Have removed the air cleaners with the same effect. Finally removed the last three plug wires and car started and ran as previously mentioned so I am assuming that is the problem. Car is running on the front three cylinders. If this is the case, why:

1. If there is fuel, air and spark why is there is no ignition in the back three cyl.?
2. Why does the rpm increase or decrease if I adjust the back carb if the back cyl. are not firing. The carb cylinders moved up and down together.
3. What if any electrical problem could cause the back cyl. not to fire.

If there are thoughts I would appreciate hearing them. I will put another fuel pump on but don’t think that’s the problem. I appreciated all the responses!
Randy Palsgrove

1. and 3. Firing order wrt dizzie rotation? (4-cylinder is *anti*-clockwise). Timing light flashing on all six plug leads? I have had a fault on my daughters car where the coil lead flashed once for each cylinder but the plug leads didn't, the cap and/or rotor were breaking down. Swapped round/replaced plugs?

2. The engine will run faster if the carb butterfly for non-firing cylinders is opened. Opening the butterfly reduces the vacuum, hence the engine is doing less work, hence it idles faster. Same as a vacuum leak (which is what it is).

The fuel filter thing just sounds like the pump compressing the air in the filter on each stroke of the pump, the pressure dropping, air expanding and fuel level dropping as fuel is used until the next stroke of the pump. That would be for an SU pump.

BTW. There was a piece today from someone with a glass and chrome fuel filter where one end came off and fuel sprayed everywhere starting a fire. Even though he had his own extinguisher in the back he had to get out before he could grab hold of it. If it hadn't been for a tanker driver with a big extinguisher the car would have been a total loss. That brought forth comments that these filters are a known hazard.
Paul Hunt

This thread was discussed between 30/10/2002 and 04/11/2002

MG MGB Technical index

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