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MG MGB Technical - B won't start on cold mornings

Hi

My 73 B is a bugger to start in the morning. It starts off turning quite well but not firing and then it just goes to a slow turn. I have to boost it with jump leads or booster to start it. That still takes some time. As it's firing there is a loud pop and then it starts.

I have cleaned battery terminals, main feed to starter and earth strap. Have checked the water levels in batteries and they are charging at 14.8, 13.2 with lights, heater, etc.

any ideas?
Matt

Mine will not even think of starting without a good choke.

(and sometimes too, a kick in the seat!)

Have you checked the linkage to/for the choke? That'd be first on my list.

How does it run when up to temp?
glg

Well it is a new engine and it runs perfectly when started.

I don't think there is a problem with the choke, there's just not enough power going to the starter. I think the batteries are dead.

Gonna convert to a 12v under the bonnet, that will save a lot of ballache

Cheers
Matt

Matt. The first thing to do is to check the set up of the carbs, including the choke. Paul Hunt has the set up procedures listed on his website. It is not unusual to have to return the carbs for winter use.

You say the engine starts turning quite well, but not firing. What do you mean by "firing". If you mean that there is no spark at the coil lead or that the spark plugs are not firing, you have an ignition problem. Bad points, bad rotor, bad cap or bad leads can cause the ignition system not to fire. I have seen leads work in summer, but produce almost no spark in severe cold. So, if this is what you mean by "not firing" check out the ignition system and tune it.

If by "not firing" you mean there is a good, strong spark, but, when firing, the spark does not ignite the mixture, look to a fuel system problem.

As to the batteries. It sounds like you are still running twin 6V batteries. That can be a problem. Any battery can be capable of providing full voltage, but fail to carry the heavy load of the starter. Your voltage checks show that the alternator is charging at a sufficient voltage, but does not show if it is charging at sufficient amp rate to both run the car and fully recharge the battery. The system check does not show if there is one weak battery. Your description seems to indicate some form of battery charging system problem which may contribute to what is happening. Thus, it would be worth testing the batteries and alternator under load. Both tests can be performed on the car and should only take a few minutes. With good batteries and charging system, look to the ignition and fuel system tune for your problem. Les
Les Bengtson

How old are the batteries? Has the electrolite level dropped -- (refil with distilled water)

Though it may not be much fun, check the condition of the connetion of the power line at the starter -- dirt, grim, tightness etc. Also the connection of the battery ground, where ever it might be located on your baby.

The solenoid could cause some problems -- especially connections and possibly the contacts within -- it's just big switch.

Battery under the bonnett raises questions - issues. There's 12V batteries that will fit in original space.

I Like the change of seasons, but I'm getting harder to start these cold days too.
glg

I have been told by someone on this BBS that "it doesn't have any bearing on the issue".. but I still believe that the oil in the carb dampers should be topped up. The oil is the resistance that stops the carb piston from rising and thereby leaning out the intake air/fuel ratio. There is quite a bit of air entering the engine upon the initial attempt to start the beast, when the batteries are fully charged and the engine turns quickly. Check the oil in the dampers just in case. Just guessing... FWIW Alan
Alan

Alan. An interesting point. Lack of oil would certainly allow the pistons to rise more quickly and oil that was too thick would delay their rise. While it has been a long time since I lived in a place that had cold winters, when I did, we used 20W-20 oil in the dampers which seemed to provide good performance in both winter and summer. Les
Les Bengtson

An MGB should be a good starter in cold wewather, especially what is passing for 'cold weather' in the UK at the moment. Steady-speed slow cranking is probably bad connections in the heavy current circuit. Cranking that starts off fast, then gradually slows, could be a weak battery or just that you are having to crank it too much. It should start within 5 seconds, I would say. Fast cranking that suddenly slows is either a bad battery or bad connections. But the difficulty in starting is probably down to the setting-up of the carbs, including choke, and ignition, or maybe how you are using the choke. IME experience they need full choke and feet off the pedals to start, my 4-cylinder can then be instantly moved to half choke, whereas the V98 will only tolerate gradual reduction. You shouldn't need to move the battery to the engine compartment, the other 512,242 didn't need it. As well as tips on setting up carbs and ignition you can find out how to check your heavy current connections on the web site that Les kindly mentions - http://www.mgb-stuff.org.uk in the 'SU Carbs', 'Ignition' and 'Electrics' sections.
Paul Hunt

Les,
Its not so much a matter of the type of oil. Rather the fact that there may not be any oil at all in the dampers. Therefore no resistance ( other than the large light spring inside )against the pistons which would cause them to rise too fast,too easy and thereby make the mixture too lean... because the pistons snap up too high at start. This is a constant depression type of carburettor, and piston resistance from the oil within along with jet height, determines how rich the mixture entering the engine is. Jets may need to be reset as well. Too lean + cold day = no quick start. FWIW Alan
Alan

If the pistons rise faster/higher pulling the needle out of the jet,without the throtle plate opening, would the mixture be lean or rich? RIC
R E L Lloyd

Ric, my opinion: Lean. There's precious little airflow to be had at the few hundred rpm the starter puts out. With the throttle between the jet bridge and the cylinder, closing it decreases air flowing over the jet bridge. Add to that the piston rising (larger venturi, same air flow, so lower air speed), and you've got a very small pull of fuel. However, I doubt there's enough air flow to move the piston much at that low engine speed, so it's probably not much of an issue.

However, Matt says:

1) It starts off turning quite well but not firing and then it just goes to a slow turn.

2) there's just not enough power going to the starter.

3) have to boost it with jump leads or booster to start it. That still takes some time.

4) Well it is a new engine and it runs perfectly when started.

First off, you've said the motor is new. Have you notified the rebuilder of this problem?

How long does it take the starter motor to slow down? Is it several seconds, or several minutes of cranking?

You have said that the starter motor starts spinning well, then slows down - we assume that's with only the car's batteries. Please tell us how it acts when the boost cables are attached. Does the starter turn faster? Does it turn the same speed, but not slow down? Does it act exactly the same?

The more info you give, the more you'll receive.

Matt Kulka

Well thanks for the response.

As the car is tuned very well and the oil in carbs etc. is fine I figured out it's the batteries.

When I put them on charge the chaRGer went up to 7 amps which meant they were low as(sorry, not very technical) so I bought a 12v battery, am going to stick it in the boot and use a cut off switch between the new batt and main feed as a theft preventer.

I think the batteries were laid up for some considerable time, they ticked over in the summer with the warmth but as it's the first winter it's been driven in, it has hit hard.

Cheers

Matt
Matt

A 12V battery can be squeezed into one of the 6V holes with only a small amount of hacking/bodging/bludgeoning. Can provide a photo if required, and it sure beats even healthy 6 volt batteries. Don't put the battery in the boot, it may not be safe in an accident.

Cheers,
--
Olly
Oliver Stephenson

One thing I didn't see anyone mention is the engine oil weight. The factory recommended 20/50 is brutal on starters and the goo can make a car w/a good battery spin very slowly. I usually switch to a lighter weight like 10/30 for winter use or try a synthetic.

I think you idea to move the battery to the engine compartment isn't a bad but you may also try using 0 gauge welding cable from the battery to the starter which should also help as it reduces resistance and generally allows more current to flow to the starter. I plan on doing excatly that when I restore my car. I think the wire gauge as supplied from the factory is just too thin for the run length. Welding cable is also far more flexible than standard battery cable. One more thing I plan to do is run a ground from the starter motor mounting bolt to the body which should also be of some help.
Mike MaGee

Even a new battery doesn't turn the engine all that well, especially when ambient temperatures are cool. And short trips will not restore the charge dissipated.

I not only keep a trickle charger attached, but if the MG has not been driven within 24 hours or if it is cold out, I find that attaching a battery charger in the "start" position fires right up.
Dan Robinson

The '71 GT I had 10 or so years ago started every time in the winter on the 1st or 2nd try, every time, no jump starts needed. No matter how much snow, no matter how cold - and this was a winter when it got down to 0deg F on a very regular basis andrarely above freezing. Car was kept outside. In the snow. With 20-50 oil in the engine. Battery in the battery box. Moral to the story is, as Paul mentioned above, that MGs should start in the cold. If the car doesn't, there's something wrong with it, probably the state of tune. Matt, as I understand it, your starter is spinning the crank around in the engine without the mixture igniting in the cylinders until the batteries run out of oomph. So either it runs out of oomph before the engine really has a chance to fire up, in which case you need a new battery, or it's cranking a long time (just how long does the engine crank without firing or before it slows down?) and then running out of oomph. If that's right, it's not firing because theres something amiss with the ignition or carbs. Is the loud pop a backfire? Engines in good tune don't do that. Oh, and don't put the battery in the trunk. I think that would qualify as a "bodge."
Wade Keene

A point overlooked by many:

A good earth connection between the engine and the body/chassis. A bit suspect here as the engine has been "done" recently ??? Check it please.
If that connection is not good or even missing the current has a problem finding its way back to the battery.
Bas

12v battery in a 6v hole: I came to replace the POs 12v but the length of the battery was longer than the hole. He had had to bodge the cradle underneath to make it bigger so I wondered if he had somehow put the battery in from underneath and welded it in. But then I realised I could tip the (sealed) battery on its end and that way it came out the hole. Went back to twin 6v and have been quite happy.
Paul Hunt

Paul. Since you are a qualifed engineer, perhaps you can provide some information here. Most of us cannot. Many have claimed that the technology of the 6V battery has remained the same since the 60s while the technology of the 12V battery has gone far beyond that. Is that true? My 68 GT was purchased with a 12V battery in it and that is what I have used since that time. Never had a problem except that the current battery had this lip around the outside due to the integral handle, a plastic strap, that was on it. Took a few minutes with a coarse file to get it to go in properly. However, it rarely gets down below freezing here in the desert, thus, I do not know how the single 12V would compare to the twin 6V batteries in really cold weather. Does it really matter? Les
Les Bengtson

12V Battery Placement: The guy I bought my 69 GT from moved the battery placement from under the rear seat to the spare tire area under the rear shelf. You can fit a bigger battery back there next to the spare tire, and we all know a bigger battery can hold more juice. Just drill a couple holes in the sheet metal and run your battery cables over the rear axle. The rear shelf keeps the battery from jumping up on bumps and lots of tools for emergency repairs are strategically placed to keep the battery from sliding around. I guess one could attach a hold down bracket, but I haven't found it necessary.
D Gesse

Matt,

THE FIRST thing I did when I bought my MG was replace the two 6v batteries it came with. I measured up one battery bay and went down to Halfords to find a battery that would fit. Turned out to be the battery of a Toyota landcruiser, a big b@st@rd battery, but any that fits will do. I bought new terminal onnectors and a new earth wire at the same time. Never had problems starting since (at least not due to a weak battery).

The person who said that a modern 12v bat is better than two modern 6v is absolutely bang on. In fact there is no comparison.

AH
Andrew H

Les - as far as I can tell I'm the only 'Paul' on this thread. I'm not a qualified engineer, but I am a qualified technician - there is a difference in the UK at least. I've no idea whether a modern 12v battery performs that much better than modern twin 6v's as I had to change the 12v in my roadster quite soon after buying it. What I can say is that the replacement 6v batteries were a great improvement over the duff 12v! They start the engine in winter after standing for a month without any difficulty or a battery cut-off switch, but then both my cars are good starters ;o) I'm on my second set of twin 6v in the roadster after 13 years of mainly summer use, whereas I am on my 4th 12v battery in the V8 after 9 years, several years of daily driving but now about the same amount of annual mileage as the roadster. I have found on the V8 that daily driving tends to hide failing batteries as they only have to hold a charge overnight, with less frequent use they can fail to start the car after just a week. After the 2nd failure in less than 4 years I have now fitted a battery cut-off switch to the V8 as I suspect its sophisticated alarm may be draining the battery even when not set. It is claimed that 6v batteries use old technology, I have no way of knowing whether they do or not, but I see no reason why modern technology cannot be or is not used in 6v cases. There are also two types of 6v battery to my knowledge - the original 'tar top' batteries with black screw-tops and exposed cell links and more recent types with red screw-tops and concealed cell links. Whether these differ or not in technology again I do not know. Whilst 6v batteries are available I shall continue to use them, but then I'm a dinosaur.
Paul Hunt

This thread was discussed between 08/12/2003 and 11/12/2003

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