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MG MG Y Type - Running rough

The old girl has developed an annoying feature of running very rough - missing - at any speed over about 48mph.

The timing has been checked and is apparently OK.

Any other suggestions of places to look?

Need it sorted soon or we will never make it to the Sping Run.

Thanks in advance
Murray
MG

If the timing is correct, and the points gap is correct (check them), it could be the tappet valves are not correctly gapped so check them.

If all of that is correct, and you have a very healthy spark at the points, check the spark plug gaps, and also the condition of them, and color, to check your mixture is correct. Basically do a mini-service check.

If all of the above checks out OK, it could well be that your distributor needs refurbishing. If so, I can HIGHLY recommend that you contact Masaaki Sakaguichi - see the Links page under Distributor Rebuilds. Masaaki owns a Y too and his work is fabulous. He has done two rebuilds for me with superb results and provides much better value for money than any other rebuilder I can think of.

When you send him your distributor, send it using the UK Post Office service of AIRSURE - tracked and insured door to door. The UK Post Office service of International Recorded only tracks an item until it leaves the UK and is useless.

Paul
Paul Barrow

Its worth checking your fuel filters etc, as the fuel may be restricted.
Steve Randle

Steve has a good point there too.

If you do not have an after market fuel filter installed in your fuel lines, there is (or should be) gauze ones on the fuel pump intake side union I think from memory and one on the fuel intake to the carburettor float bowl (2 if you have a YT/twin carburettor set up).

If dirt is by-passing these then you should be able to see some accumulation in the bottom of the float chamber too that will need to be cleaned out.

Thanks Steve for the reminder too.

Paul
Paul Barrow

Thanks chaps. I'll let you know what turns up

Murray
MG

I can only add that in chasing a fault, carry out changes one at a time and if doesnt work put it back to the original before trying something else.
If it is the fuel supply then after running down hill the engine will pick up for a time at the bottom. It sounds to me like a coil or contact breaker or perhaps condenser. The car will run on a coil from any motor factor.
I had recently on my 105e Anglia two of the spark plug lead suppressors go open circuit. They should read 7 to 11 K ohms I found that two spark plugs were sooty although the compression on all cylinders was about 160Lbs this indicated an ignition fault.
All the best.
Bryan

When this happened to me last year, it turned out to be fouled spark plugs caused by a too rich mixture. I had to clean the plugs at 1000 miles intervals. Ultimately, I reconditioned the carburetor and changed the needle for a leaner type and VOILA! The car runs like it just left the factory.
Gilles Bachand

Good thinking Gilles The problem with these old motors is that they develope faults that would not happen when they were new.
Bryan

I had the same problem as Gilles - the brass nut at the bottom of the carb had split in it and the needle was worn - replacing both cured it. A similar problem later on was cured by fitting new copper leads - the ones on my car were iron wire type and were over 30 years old and had gone hard etc. Other things to look at is the points - the modern reproduction points usually work ok but are not as robust as the older Lucas ones. Might be best to take the carb off and clean it as well as checking the needle lifts OK. I find a 15thou gap in the points works better with modern fuel than the 12 thou suggested in the manual.
David Mullen

Thanks for all the help and tips. For those who were not at the Spring Run and who want to know the answer, it was the regulator.

It was not working and thus not charging the battery and battery power alone is, apparently, not sufficient to supply the required spark at speeds above about 48 mph.

We got the regulator charging properly and set off for the Spring Run. 50 - 55 was no problem. Just outside Oxford the ammeter showed no charging and shortly after that the rough running returned.

We decided to abandon the trip and returned to London for a more modern MG to enjoy the weekend.

A new regulator (number 2, or is it 3?) is on it's way.

The reason for not suspecting this earlier is that I still have no idea what "normal" looks like on the ammeter as I have had a string of electrical issues.

Murray
MG

Murray:

Sounds like a frustrating experience with your car's electrics!

There's no single answer to what "normal" looks like on the ammeter when your charging system is running properly.

When you start the engine, you should notice that the charging rate is quite high (up to 10A or more) for a few seconds or more - this is while the dynamo and regulator arrange to replenish the battery.

When you're running at cruising speed, the ammeter should show a much smaller positive charge (maybe 1-2A) once the battery is up to charge.

If you turn on the headlights or wipers while at cruising speed, you will see the ammeter run into the negative zone for a few seconds, then return to the positive zone and stay there as the regulator adjusts to the new load.

It seems unlikely that you have two completely duff regulators. It may well be that the regulator you have needs adjusting to provide more current at a given engine speed. The procedure to do this is straightforward - reach for your copy of Blower and follow the steps! You'll need a voltmeter and a fine screwdriver and spanner.

All this assumes that the dynamo is doing its stuff properly, of course - has this been eliminated as a potential problem?




Tim Griggs

Tim has covered it pretty well but if you are not confident about fiddling with the Regulator (and I dont blame you if you are) then seek out a good old fashioned small Auto Electrician in the back streets with a nice grubby old shop full of old dynamos & starters. Getting it wrong can cause an over-charge and a fire.

Paul
Paul Barrow

The new regulator (from Holden UK) arrived today so it will go on tomorrow. I have only ever seen 0 or +20 on my ammeter (except when I turned on the lights)

I have yet to see the sort of variable response you mention, Tim, but fully understand that this is what it should behave like, and why.

An enthusiastic amateur connected a previous regulator up incorrectly (it was full charge under any conditions) and burnt out the resistor in the base. I mentioned this in a previous post a few months back and the flood of "change it immediately"s that came back from the bulletin board had me scurrying down with a screw driver to trace every wire and ensure all was as per the diagram.

I'll see if I can locate said old-fashioned auto electrician and get the original one serviced. There is a company here that does reconditioning for £175 but new ones are only £99.

Murray
MG

You may well have tried this but refering to the image, so often the 'E' is not firmly making good contact with the body of the car, it will cause all sorts of problems if faulty. 'D' goes to the larger stud on the dynamo and 'F' to the smaller stud. 'A' to the ammeter and 'A1' to the lighting switch. But try that 'E' first.

best of luck
B Mellem

As a second thought, I see from the circuit diagram that the earth for the petrol pump is connected to 'E' on the regulator, so if there is a dodgy contact to the body it may be a problem. It is better not to rely on giving connections a good tug because brass to steel contact will act as a mini battery and oxydize.

As for misfire, as high demands are made from the engine I read somewhere that as the combustion pressures rise then demands from the ignition rise. I found that pitted contact breaker gave just such a misfire.
Bryan

I installed the new regulator this afternoon and after a short run I can say that at last I have a regulator which performs like a regulator should. The ammeter charges at variable amounts, kicks in after a short delay with headlamps on etc etc.

Now, all I have to do is find out why it still keeps drinking water like a parched camel.

Thanks again for all the suggestions

Murray
MG

Murray

If you are not getting emulsification in the valve cover, or excessive steam from the exhaust, and there are no signs of water droplets on the dip-stick, your head gasket is probably OK.

The next obvious areas are hoses - perished or not connecting properly. The worst one to get on properly is the radiator bottom hose, so check that.

Also, check the radiator and engine drain cocks, that they open ... and close fully. A piece of debris preventing full closure will give you an annoying loss!

Then look at the core plugs along the engine block for signs of weeping around the edges. If they are, drain the engine of water and when totally dry, you can stopper them up with epoxy putty, pushing it well into the edge of the core plug/hole in small amounts. Dont go for big globs - it wont stick half as well. Some of these are a real begger to get to with the exhaust in place though, so be warned!!

Finally, the one you cannot see is the rear plate at the back of the cylinder head. If you can get a video boroscope (I bought one the other day - $300 NICE!!!) to have a look back there you may find one of too things - 1) the plate wasnt put back on square with a nice new gasket on clean surfaces, or 2) the plate has rusted through and has become pourous. Either way, about the only way to get at it is to either bust you knuckles with some ratchet spanners/wrenches, or pull the head off with all the attendant pain that will entail replacing the head gasket.

Paul
Paul Barrow

80 miles today, out to Nether Winchendon and back, a spot of torrential rain, quite a bit of other wiper use and a regulator that worked all day! Yippee! Humming along at 50 - 55, running a sweet as can be. Oh, the joys of owning a Y!

2.5 litres of water for the round trip. Hmmmmm ....

Just another little issue. I am sure it is not a static leak but will investigate fully.

Murray
MG

Murray: glad the regulator problem is sorted.

You mention only ever seeing 0 or 20A on the ammeter. It sounds like the big ballast resistor on the underside of the (old) regulator had failed, so that the dynamo was effectively on or off. This can be replaced. Mine failed while the car was being rebuilt - the resistors apparently decay internally and simply cease to function. But keep the old regulator for spare.

As to the water leak, sounds like a new thread to me! 2.5 litres in 80 miles and no sign of water in the oil could very well be an external leak or a water pump gland failure?

Tim Griggs

Here's another gremlin which caught me out with the TF.
Thinking a petrol filter was a good idea I was puzzled after a couple of thousand miles that the car was loosing power. Well no suprises the filter was blocked, but it caused great consternation one dark night on a country road after the car failed on a hill especially with my wife who complained that the YA had never let us down. I have now fitted a very much larger filter. I am afraid it has'nt assured the wife!
Bryan

Bryan - did you fit the larger filter to the Y or to the Wife?

P
Paul Barrow

Just you try that one Paul! It will be the end of my Sunday roast and cakes for tea.
Bryan

This thread was discussed between 26/04/2009 and 19/06/2009

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