Intermittent misfire/cutting out - advice please

[palacebear]

My Moggie has been started regularly and driven approx once a month over the winter. The last two drives have revealed a slight misfire under sharp acceleration (both occasions after around 5 miles of trouble free driving from a cold start). The misfire then gets worse with intermittent loss of power followed (at around the 9 mile mark) by the engine cutting out. When I try to start it again it turns over fine but doesn't seem to fire at all, although after a 30-odd minute rest, it restarts straight away. The fuel pump sounds like its doing its job ok and, with the feed pipe to the float chamber removed, it delivers a healthy shot of fuel which is handy for cleaning the inner wing I'm assuming electrical issues and whilst we point fingers at the condensor fairly readily, could this be the coil breaking down? Your opinions please...?

[Trickydicky]

It could either be the coil or condenser but don't also rule out the rotor arm. If you replace the condenser, buy one from the Distributor Doctor, you can also buy his great quality rotor arms too. If you have a multi meter a good coil should read 3 ohms resistance.
Also check the condition of the HT leads in case they are breaking down.
Start with the obvious culprits but as noted in previous posts, coils rarely fail but it's not unknown.

[BrianHawley]

So the problem seems to be only when the engine has been running for a while and goes away if you leave it for a bit. Off the bat it sounds temperature related. Could still be electrical, but I'd be more inclined to suspect fuel vapourisation or a mechanical expansion effect.

Does the carb get hot? How do the plugs look? Have you checked compression, cold and hot?

As an outside bet, any pin-hole water leaks spraying the electrics?

Remember it's never the condenser - except when it IS the condenser

[dalebrignall]

it could be 101 things , points pitted , and gap not correct , could be condenser failing , could be distributer cap , coil breaking down , or bad connections to the coil . i would be inclined to look for a loose connection before spending any money . check the terminals on the coil are not loose , also check the spade connectors and the wired to them are good and tight . i had a wire comme off the coil last week on the m25 and lost all power , lucky for me i was able to pull off and i had another connector i could put on and made it home , did a propper repair the following day . also look at the condition of the plug leads . good suppliers of ignition parts are accuspark , or distributer doctor

[palacebear]

Thanks to all for the input. Coil leads appear secure. No water getting onto electrics. Dizzy components look pretty elderly so will change points condensor rota HTs and cap as a matter of course. They may well have been on there since resto (14k miles ago in 1990!). Not had chance to look closely at carb yet. Will get my local Minor-friendly garage to check compressions next week if I can. Should also mention that when the engine is idling there's an irregular 'pop' in the exhaust note (not a backfire). Won't be able to do too much this week but will tell you how I get on soon.

[oliver90owner]

First check, before interfering with anything, is to test for spark and quality (if there is one) when the engine will not start. That will, at a stroke, determine if the fault lies within the ignition system, or elsewhere.

If the spark is not present at the plug leads, check at the king lead from the coil. That way the fault might be isolated to one partucular part of the system.

[palacebear]

Today's efforts: Started fine from cold. 5 mile round trip with stop for petrol at the halfway mark. Took about 2.5 gallons to fill right up so gauge isn't at fault. Drove ok throughout journey. Oil level checked and ok. Coolant checked. About 1 pint needed. Coil and fuel pump slightly warm to touch (both about same temp). Left car idling for about 45 mins giving the throttle the occasional 'blip' with no problem. Last 'blip' and felt like a big 'flat spot' then slower idling and engine died when throttle opened. Wouldn't re-start. Fuel pump still felt same temp. Coil still touchable but quite hot. Plugs are fairly new but very sooty with gaps of 15thou. HT leads look ok but screw-in connection to coil looks a bit hit-and-miss. Coil cap looks slightly oily but might be down to my fiddling with the dipstick (no euphemism!). Dizzy cap has seen better days. Brown outside. Black inside with green mould to add some colour. Ran out of time to look at points condensor or rota but I think I know which way the wind is blowing now. BTW head is not unleaded so I use Castrol additive at about 200ml per tankful. Exhaust smells pretty rich. Methinks a good service and carb clean will solve the problems... unless of course it IS the coil

[oliver90owner]

Was there a spark at the plugs when it would not start? That is a very simple and basic test to check whether to pursue the electrical side as culprit, or not.

[palacebear]

Stupid of me. Overlooked this simple test today. I keep getting interrupted to do other 'more important' domestic tasks. Apparently a mossy lawn takes priority over a poorly Minor Will have to wait until next week now but I'll test it and report back!

[dalebrignall]

the points gap is 15 thou and the plugs are 25

[kennatt]

sounds like you have a few issues,first clean up the dizzy cap,to get rid of the green verdigris(Mould as you call it) just use fine emery or just gently scrape it off the contacts,its possible that you MAY need a new cap if the contacts have corroded too far,but try cleaning first . clean up the lead contacts.
when you say the coil is hot,how hot.and are you sure the oil is from the dip stick,or is the coil leaking,The coil normally will be warm but not hot,it also gets heat transfer from the engine,(Hence why its a good idea to move it to the inner wing with longer leads) It will get very hot if the ignition is left switched on for a long period . Sometimes it is the coil(Here comes the bolt from the blue )
sounds like the engine is running a bit rich,could be left ticking over has caused flooding .
Screw large nut under carb,right up then back down 12 flats
When did it last have a new air filter.
When no starting/stopped running Check spark, if ok remove air filter and run some petrol into carb to prove petrol supply.
you basically need to try to isolate which system is causing the problem before progressing

[palacebear]

Some success today. Cleaned and re-gapped plugs. Mixture adjusted by 5 flats of the nut. Smoother driving. Smoother idle, with more even, less noisy (and less smelly!) exhaust although idle speed a bit fast at the moment. Still some hesitation but not as bad as before. Carb damper feels like no oil in it. Not a quick job on my car as its got the old cylindrical gauze air filter sitting on top with the intake duct and supports in the way of everything (see pic). Idle screw siezed and now soaking in WD40. No time to do any more this week. Thanks again for all suggestions. Will slowly work through them next week and report any earth-shattering developments!

[BrianHawley]

Great that you're making progress.

Sometimes it's not just one thing. The A series tolerates one slightly maladjusted or dysfunctional component fairly well, but a bunch of them can add up.

Good luck.

[palacebear]

Thanks to all for suggestions and opinions. I'm going to end this thread by saying that I've done some tweaking and adjusting. It's made some improvement but whilst doing the adjustments and driving the car I've found other more serious defects which need fairly drastic action. I'll be putting this in a new thread and asking for advice (again) when I do.