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MG MGB Technical - revs drop car stalls

Hi if anyone can give me a steer before i end up spending a stack of money on this , here is my problem and its been on going for about a year. Start the car with a little choke she runs fine temp gets to 185 oil pressure reads 80, in goes the choke and away we go pulls good right through the range cruise at about 80mph for abbout 30mins see my junction and start to slow down sometimes i hear the odd little pop or splutter but nothing to bad just as i stop the revs just keep falling until the car stalls she always starts again and of we go untill we reach the next junction. I have ajusted the idle speed to 1200 revs which helps but ive just noticed that when i depress the clutch the idle speed drops by about 400 revs i think that somehow this is connected with my problem oh checked the plugs they have a sooty ring around the thread but the bit in the middle seems text book any thoughts on this thanks
Richard H
Richard H

An occasional pop or splutter? Then something is wrong!

When it dies at a junction can you keep it running on the throttle or not? Is the tach steady? Flickering? Or dropping to zero when it stalls. How old are the plugs? Points? Leads? Cap? Rotor arm? When did it last have a proper ignition service like dwell, timing, correct operation of the centrifugal and vacuum advance mechanisms? When did it have carb needles? Jets? Full set up of air flow and mixture balance of the carbs? Unless you know it is set up correctly you are just going to be poking and hoping.

Some drop in revs when the clutch is operated seems quite common (although neither of mine do it and I've nver been aware of any past car doing it either) but 400rpm seems a lot, and as such could reflect a very poor state of tune.
Paul Hunt

Paul when the revs drop if i am quick, and tap the throttle she picks up However i must admit when she is ticking over the engine and the revs are bouncing all over the place i think you answered my question its time for a proper tune ect
Cheers mate
Richard H
PS any idea how much i should be paying for a full tune and balance i just forked out 3k on a mgoc respray and have since been told they saw me coming although the finish looks the dogs B"£$%&*S
Richard H

Erratic tach indicates problems in the ignition LT circuit. This could be loose connections anywhere through the ignition switch, coil or distributor, or manky points. There is also a ground wire inside the distributor which is continually being flexed back and fore, and although a very flexible braided cable it can break at the tags. The coil wire where it passes through the distributor body is also flexed back and fore and the conductor strands can break inside the insulation. Both these can cause an intermittent contact. As this flexing happens when the throttle is changed, this could explain why it cuts out when you lift off, although if you can catch it on the throttle it may be sticking carbs.

As for how much I haven't had a car of mine serviced at a garage for probably 30 years so I haven't a clue. But you *must* take it to someone who knows this era of car or they won't know where to plug their diagnostic computer (I could tell them) and not have a clue how to set up twin carbs, even if they know how to set up points. Even then some so-called mg specialists leave a lot to be desired, try and get some personal recommendations for your area.
Paul Hunt

Nice one paul that gives me a half chance i will have a poke about this weeekend i spent many a weekend sorting out my old mini years ago and apart from the carbs this engine and ignition circuit seem the same so far ive changed the head gasket on this mg but have not done much else but the steer to the LT circuit gives me something to aim for. One of the great things about this site is the knowledge that people like yourself impart,
Thanks
Richard H
Richard H

This thread was discussed between 26/01/2005 and 27/01/2005

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