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MG MGB Technical - poorly MGB again

I started my 1976 MGB yesterday only to find that it seemed to be only firing on 2 or 3 cylinders, and would not tick over it just kept stopping until I finally flattened the battery.
Admittedly I have not started the car for at least 2 months but it has been in my garage under cover. The last time I used it the engine ran really nicely.
It has a good spark at each plug. the misfire is consistent and rhythmic, which makes me think electrics, Any Suggestions will be very welcome,

Trev Walton
Trev Walton

trev,
just had that trouble with mine, condenser. if you havnt got electronic ignition.
bob.
1970 gt.
Bob Taylor

I have had this a few times and it has been one of the carbs flooding. You can quickly check this by looking at the overflow pipes. Last timwe it happened all the plugs sooted and I could only find 2 clean ones when i wanted to re-start after fixing the float valves. Just swapping 2 and then firing up soon got the all 4 firing fine.
Stan Best

If you do indeed have a good spark at each plug then it can't be electrics. If it's only firing on 2 or 3 then maybe one carb isn't functioning, maybe the float valve has stick closed and the float chamber is empty.

A flooding carb could be a possibility if the fuel pump continues to click when the ignition is on but the engine hasn't been started. But on a UK car that should immediately be dumping fuel on the floor and evident as a strong fuel smell in the vicinity.

A bit tricky with an engine firing on only 2 cylinders, but if you can get it to run with each plug lead disconencted in turn theh you should be able to determine which cylinders aren't firing.

Are you sure someone hasn't been in and swapped the plug leads round in the 2 months it hasn't bene used? Firing order is 1-3-4-2 *anti*-clockwise, but tou have to get No.1 right first. The easiest way to do this is remove No.1 plug (at least) and turen the engine manually with your thumb over the plug hole. When compression starts lifting your thumb off the hole, that is the compression stroke. When that piston reaches the top of the cylinder, the notch in the crank pulley should be by the TDC mark on the timing cover pointers. Whichever distributor cap contact the rotor is pointing at goes to No.1 plug, and you count the rest from there.

How did you check the spark? If you only checked the spark between the lead and the contact on the cap the plug could still be faulty. If you removed the plugs and laid them on the block, sparking in free air takes less HT then when under compression, and it is quite possible for a faulty cap and/or rotor to break down when the plug is under compression but not when it is in free air.
Paul Hunt

Thanks for your comments but can you beleive this, the next morning I charged the battery so I could work on the car after work. When I got home the car started and it ran normally firing on all cylinders. So now im really baffled, but at least the car is well again. I will start it weekly over the winter. Trev.
trev walton

Trev,
Given that it is now running OK, is it possible that you had a damp distributor cap that has now dried out?

David
David Overington

Trev. If you have had a coolant leak and coolant got onto the dist cap it will attract moisture and act as yours did.Glycol is hydroscopic and it permeates the cap. Later in high humidity you can have a problem with a cold engine. It seems to dry up as the day gets warmer and then will run okay.
Sandy
conrad sanders

Shouldn't need starting weekly, I start mine monthly if I can't get them out due to bad weather, the battery itself should last 2 or 3 months or more unless you have an alarm. I've still added a battery cut-off switch though, as much for safety as anything as the roadster is at a remote garage. Run it for 20 mins or so at a fast idle (wedge under the throttle pedal back-stop, not the choke pulled) with the heater fan blowing on the interior to help dry out any internal dampness. I also jack each corner up and turn the wheel 1/4-turn, one year it was left about 3 months and when I next drove it it was like a clown car with eccentric wheels, I could feel the flat-spots bouncing the car up and down as I drove along. Fortunately they were OK again after a brisk 40 mile drive.
Paul Hunt

This thread was discussed between 23/10/2008 and 27/10/2008

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