Mgb cutting out when hot, out of ideas!

[Dbest92]

It's still on its old points at the moment

I'm starting to wonder whether the distributor is worn as the lobes on the cam look worn but it all feels tight, my midget spoilt me for this and has done many thousands on miles in its current points with no need for attention!

It's had a few 20 mile journeys and touch wood has been trouble free, since replacing: leads, cap and red rotor with another red rotor, also have cleaned the inline fuse which controls the wipers, radio and fn, these didn't work before. Finally after fiddling around with the points, they have ended up around 20 thou and the car seems to be running better for it which is strange, but seems to be ok at the moment.

I'm thinking about in time looking down the electronic ignition route, but as yet undecided, if the car stays running ok I won't touch it! But was wondering if you had any recommendations on which ones are better?

Cheers

[New POD]

Condensor. You can't buy decent quality one's these days so you'll fit a new one, and a set of st points and 8 weeks later it'll be misfiring again.

[nta16]

Dbest92 said:

It's still on its old points at the moment

good leave them in, check gap in a couple of weeks or couple of hundred miles, then leave to next service and just clean and regap as required

Dbest92 said:

I'm starting to wonder whether the distributor is worn as the lobes on the cam look worn but it all feels tight

unless you put up a very close up (in focus) photo difficult to say but I doubt that where the wear is plate and springs - do you not follow any of these links I put up

Dbest92 said:

It's had a few 20 mile journeys and touch wood has been trouble free,

so time now to increase the journey length in stages then a few blow-out runs of 100-200 miles (the Italian tune-up) you be surprised how much better the car will fell after those, if you don't leave the car unused

Dbest92 said:

Finally after fiddling around with the points, they have ended up around 20 thou and the car seems to be running better for it which is strange, but seems to be ok at the moment.

the book figures may not be exact now for a 30+ year old car but they are a guide starting point at least, if your mechanic set the tappets, then points, plugs and timing followed by the carb mixture and he stuck to the gap by the book I think you should too (if he gapped a bit wider fair enough but you'll have to ask to be sure) and check the plugs are gapped to the book - the checking at service intervals will deal with and closing or widening for both

Dbest92 said:

I'm thinking about in time looking down the electronic ignition route, but as yet undecided, if the car stays running ok I won't touch it! But was wondering if you had any recommendations on which ones are better?

don't worry about it for now, there are loads of igniter heads from inexpensive to expensive all need to be fitted carefully or you'll have a car that misfires and/or doesn't run - loads of opinions of which are best and those that say stick to points

then there the fully electronic dissy much better choice but have look at the price and you'll see why you'd best wait

if you want to be traditional you could have a rebuilt dissy with points and condenser guaranteed for 3 years by you (should) know who

these will improve the running of the car but could be let down by other components, taking the condition out of balance - if your dissy integrated over night then may be fit one but not while the rest of the car's condition is unknown and other more vital servicing, maintenance and repair work may be required

now it's running drive it more that will help to improve it

how much of the 36k-mile service/check-up has been done?
tyres, brakes, brake fluid, coolant system cleaned, oils front to back, suspension, steering, lighting, windows and mirrors ??????

the quicker these things are sorted the quicker you'll get to drive the car in better condition and spend almost all your time driving the car and very little working on it

ETA: have you got three cars, two classics?

[Dbest92]

Right, back to square 1 again!

Same again after just 4 miles today (sometimes lasts up tp 15/20) it started misfiring and losing power, then cuts out, give it 10 mins and it'll do about a mile and same again. Rev counter stays steady and ignition light stays off until it finally cuts out.

Has had a new coil, all leads replaced and checked, new points and condenser, gap stays where it should, tested with old and new ones, a few red rotor arms, distributor cap and leads and spark plugs, fusebox and fuses, fuel pump has been replaced, carbs cleaned and fuel flow checked under different conditions, timed and tuned, fuel cap has been removed to test vacuum in the tank, the vacuum advance works on the distributor and wiring has been tested

Completely out ideas, getting irritating now as there's been too many hairy moments beside the road and dual carriageways and its been pretty dangerous especially when there's no hard shoulder and the car has no hazards, plus the specialist garage is a fair way so can't easily get there and there aren't and decent classic garages locally

Any ideas would be really appreciated!!

Edited by Dbest92 on Sunday 5th May 20:49

[MGJohn]

When I read the OP my first thought was, as already suggested, fuel vapourisation from under bonnet heat building up as engine warms. Try a simple check by wrapping fuel lines to the carbs and closeby with heat resistant material.

The fact that it restarts when allowed to cool is one of the signs that makes me think on those lines.

I have also known another Carb car ~ not an MG ~ would have fuel vapouristaion problems after switching off on a fast run say when taking a break at a Motorway Services. Heat soak from the hot uncooled switched off engine would affect the fuel line and starting would be difficult until the fuel lines had cooled down.

Twenty odd years ago I was pulled over on the Motorway ~ 107mph officer ~ no way would my old car do that ~ then being advised by the officer to be extra careful when rejoining the Motorway from the hard shoulder. Good advice only because of that heat soak on a hot day, my car would just about start and would hesitate for several hundred metres until cool fuel reached the fuel pump and then the carb when it would pick up. Bit 'iffy' for a while and I wonder what the Police in the patrol car behind me thought. I was not messing about honestly occifer!

[v8250]

Dbest92 said:

Right, back to square 1 again!

Has had a new coil, all leads replaced and checked, new points and condenser, gap stays where it should, tested with old and new ones, a few red rotor arms, distributor cap and leads and spark plugs, fusebox and fuses, fuel pump has been replaced, carbs cleaned and fuel flow checked under different conditions, timed and tuned, fuel cap has been removed to test vacuum in the tank, the vacuum advance works on the distributor and wiring has been tested

Any ideas would be really appreciated!!

OP, have you installed the new coil with connectors facing downwards? If not, do this as the coil will overheat and give up the ghost. All the above aside...

1. what fuel pump did you fit and was it new?
2. re-check your front wiring loom...thoroughly clean and nip up every connector.
3. check for movement on the LT wire inside the distributor...they have a habit of moving under vibration and causing a partial short which normally results in mis-firing and intermittent engine stoppage.

don't give up and sell the car. percevere and you'll crack it...and keep sharing faults with your fellow PH'ers. collectively they know their MG's

[nta16]

as above

particularly electric connections and wires (to ignition switch itself and even battery lead connections and earths)

check the ignition switch at rear and all tight with no excess wiggle between (key) positions and on key/barrel

check wires and connections to fuel pump

and check the insulation on points and condenser are fitted as shown in the drawing in the DH and are secure and that the low tension lead you fitted is secure

check dissy cap for bad pitting and that the carbon and spring that go to the rotor are in good condition and working fully as this has caused others owners problems (more poor quality new parts)

I'm trying to think of oddball reasons for this that have come up in the past but can't think of any now so will have to look elsewhere

you could check out mgb-stuff site for ideas

ETA: a few other ideas -
from a V8250 idea, and I’ve had it happen to me – make sure the HT lead boot covers are burped at dissy cap and coil (ask your mum or gran about burping a Tupperware lid to expel the air) – as if they are a tight seal the vacuum inside can prevent a good connector to socket fit, or even if you push the boot down it can lift the connector up creating a poor connection

check screws in distributor are tight and top plate isn’t loose

check plugs for cracked insulator and poor seal to engine

and for fuel side -
an obvious one for fuel problems, when it misfires pull the choke to see if things improve or get worse

Edited by nta16 on Thursday 2nd May 01:19

[v8250]

nta16 said:

as above

ETA: a few other ideas -
from a V8250 idea, and I’ve had it happen to me – make sure the HT lead boot covers are burped at dissy cap and coil (ask your mum or gran about burping a Tupperware lid to expel the air) – as if they are a tight seal the vacuum inside can prevent a good connector to socket fit, or even if you push the boot down it can lift the connector up creating a poor connection

OP, I should expand on this a little. As you know, many older cars have push fit HT leads. When pushed onto distributor cap the rubber cover traps air inside which forces the HT lead connector 'up' if they're not snug and firmly tight. So, open up the HT lead connector to the point where they're almost too tight to fit, push home fully into distributor cap and then spray a little WD40 onto HT lead end to ease fitting of rubber boot. Push home and lift the end of the boot to expel any excess air. This is the only way to really know you've got a 100% pukka connection.

+ can't remember if you've bought new leads yet - if not, buy Magnecor KV85's. They're a little more price-wise than many other lead sets but by Jove you'll notice the difference...and they'll last you many years.

[nta16]

as we've been agreeing quite a bit time for a little divergence

I'm not sure about spraying WD40 as a lube and on to electrical contacts as I remember someone telling me not to, but I've never contacted WD-40 to confirm or deny

and I think Darren has borrowed another set of HT leads anyway but as he knows I strongly recommend a company that makes leads for others to pass off as their own

these leads are well made and have been proven to slightly increase engine power by an independent A and B-series engine specialist - http://www.performanceleads.co.uk/

Darren,
I was going to wait until you reported back but as I'm here now - if you can't find the source of the fault I'd suggest taking your car to someone that has and knows how to use the old style diagnostic machines, that should find it fairly quickly

[v8250]

hi nigel, understand ref' wd40 but here it's used as a lubricant. i'm not aware of any ingredient in wd40 that would adversely affect HT leads and their connectors. i guess most of us want some way of waterproofing the electrics really...a waterproofing grease of some sort. we have been known to use condoms on some of the rally cars which always makes for interesting pub/rally office humour!

hope the OP gets the B' sorted.

[nta16]

I'll have to contact WD40 about it, they replied when I asked about 3-in-One oil which is part of their group

I look on WD40 as chasing water away rather than sealing it out

to seal the HT boots you can use a 'dielectric' grease and it helps with slip movement of the boots or I've just put a collar of silicone sealant

I've no idea of anyone who has condoms at my age !

I think Darren's just a bit dispirited with it at the moment, same way we all get with the cars now and then when they play up

[Lagerlout]

Hi, I asked a question a while back about the year of the car and the coil. I see it's a 73 - ? Can you tell me please what type of coil you fitted to the car? Have you fitted a coil marked as a 12v, or a 6v?

Your car, a CB 73, "should" be supplying 12v direct to a 12v coil (unless it's a V8). If you have fitted a 6v coil to a car with a 12v supply, the coil will overheat and the car will misfire once warm.

As these cars are so frequently modified, they are not always modified correctly.

With a 6v coil in a factory car, there is a length of resistive wire in the loom that will step down the supply voltage to the coil, for a 6v coil. If a 6v coil is fitted to a car with 12v supply, a seperate ballast resistor needs to be fitted to the car.

Conversly if you want to run a 12v "Sport Coil" in a later car, you need to run a 12v supply to the coil direct from the fuse box.

Do you have a visible ballast resistor anywhere? An oblong ceramic box about 2" long mounted to the inner wing or sometimes to near the rad?

Anyway, it could be a lot of reasons as others have posted, this is just one of them but worth eliminating.

Edited by Lagerlout on Friday 3rd May 14:32

[nta16]

good point about coil and HT side has been considered but just to say not everyone has a multimter or knows how to set the dwell (that's when the multimeters work and are accurate)

[Dbest92]

Update: progress ,

I managed to get the car to cut out in the drive at home so i could have a detailed look at some parts, car cut out and stalled as it did on the road, checked the float chambers and they were empty, problem located yay!

fuel pump pumps fine from cold, however when restarting after cutting out it appears to click fairly rapidly (which i know if shouldn't) and also appears to go slow, then fast and slow etc, car wont start like this, needs 10 mins before it will run again, i know this is something that should have been looked at earlier, but when your beside the road, first concern is getting to a safe place etc.

the garage has offered to have a look again next week. The fuel pump was new apparently and think its the SU type, seems odd for it to be packing up in such a short time? I'm wondering if its a wiring/power supply/earthing fault but aren't sure, will try and have a look over the next few days before the garage takes it in. Im not overly happy with the wiring on the rest of the car as alot of it looks old and the insulation has worn of some of the wires around the car, something i will be addressing in the near future.

Regarding leads, i have tried 3 sets on it and all appear to have been fine, interesting looking at that link as that company supplying the unrated leads is only 25 mins drive from me! May look into it in time/ i know what you mean about the leads not being on properly, on some of them you can hear them click on but some are a pain regarding getting them so seat correctly.

The car is a '73 and running a 12 volt non ballasted coil mounted upside down, the previous coil was a sports coil but now has a lucas normal 12v coil, which when left idling still gets very hot which led me down the electrics path.

so hopefully the solution is in sight! As mentioned the garage are happy to sort out the fuel pump and check the wiring etc.

Its best sometimes i'd say when your at your wits end with something like this to leave it for a few days and come back with a clear head and new ideas! It did get very frustrating as there were too many times being stranded! plus you don't realise how fast modern day traffic goes until your sat 3 feet from it in a verge!!)

Darren

[nta16]

Dbest92 said:

Its best sometimes i'd say when your at your wits end with something like this to leave it for a few days and come back with a clear head and new ideas! It did get very frustrating as there were too many times being stranded! plus you don't realise how fast modern day traffic goes until your sat 3 feet from it in a verge!!)

too true to both

well done on find this, intermittent problems are always a bugger to track down

as you may not have got so deep with links here's a short cut that might help with wiring, note look for UK models - http://www.advanceautowire.com/mgb.pdf

as for fuel pump, I doubt it'll be the pump itself but you never know, personally I don't like the original points (more nasty points) style pumps or the electronic cube or cylindrical pumps, I those and much prefer the modern electronic copies of the original, Ive got a Q&H electronic (if they're still in business), fit and forget

there was a reason for including electrical contact cleaner and grease in the tools list

Fast Lane aren't a little cottage industry just making HT leads with impressive sounding names for high prices, they're more used to high quality equipment that must be robust

good luck with your search

[nta16]

Darren,
have you got a MGB and a Midget 1500 and a modern ?

I asked earlier but don't know if you missed it, don't or skim read my long posts or don't want to say (which is OK, just put MYOB)

[Dbest92]

That's true! It seemed to point to the electrics with he rev counter initially, but as it had been off the road for so long there may have been a few other problems!

I had a look at that link, is very good and makes it seem simpler, I'm not happy with the wires to and from the coil as they're old and the insulation has rubbed off in places!

I had a look at the pump set up in a book and looks massively complicated for what it is" hence why I'm leaving it to the garage! As, as you say, would be surprising for the pump to be failing already! More inclined to think electrics!.

I have got 2 mgs and a modern unfortunately! The original plan was to sell the midget privately but it's a lovely little car and not worth a great deal so we decided to keep it and its in my dads name for now can't insure both unfortunately

[nta16]

Dbest92 said:

I have got 2 mgs and a modern unfortunately! The original plan was to sell the midget privately but it's a lovely little car and not worth a great deal so we decided to keep it and its in my dads name for now can't insure both unfortunately

thing is Darren unless these classic cars are driven regularly you'll never really sort all the faults, problems and niggles and the lack of use will introduce more

unless your dad is regularly going to drive the Midget you'll have two lots of faults, problems and niggles and the lack of use will introduce more

you could of course give up your modern car and make one or both of the classics reliable and dependable, it is possible and by someone of your age

I might be wrong but seen it so before, this time next year one or both of the MGs will come out for occasional use before going unused again because you have the time, opportunity or inclination to get either to a condition where they can be reliably other than very occasional use and eventually they'll either sit unused or be sold off

up to you but I suggest you sell one of the MGs - just my opinion, and I could well be wrong

[Dbest92]

Just an update, fuel pump has been replaced with a new electric one (not the su type) and drove home 26 miles through traffic etc without a blip. Hopefully this has cured it

Thanks to all for suggestions

Darren

[Wildcataa5b]

Darren, I suppose you have checked to see if there is a heat shield around the Carbs, my mate had his missing and the fuel vapourised at high temp.
http://www.stainlessforclassics.co.uk/twinsuhif.ht...
No commercial interest in this site - just to show you what should be there.