Running badly when hot

[Stig]

OK, this is actually the Sprite but it's still an A-series. Dug it out of hibernation yesterday, a bit reluctant to start but happy enough when it got going. Until I'd been running 30 mins or so when it stalled at a roundabout and wouldn't re-start (had been running rather roughly before that). Got it bump started (though the starter was spinning it over quite well) and as soon as I put any load on the engine it died again. Got back to it at lunchtime and it started first turn of the key and was fine for the 1 1/2 miles to work. OK leaving work but started getting rough again half-way home (15-20mins) and stalled again. After sitting for 10 mins managed to start it again and eventually got home with another brief interruption.

So, temperature related but unlikely to be fuel vapourisation - I've even got some exhaust wrap on the manifold now as it was showing similar symptoms last summer. Also, I checked the float chambers and they were perfectly cool after it stopped on the way home.

I'm guessing it's poor sparks as bump starting worked when the starter didn't. Coil overheating? Distributor cap / rotor arm? Any ideas?

[Ratbag]

Blocked tank breather?
Clogged fuel filter?

[mogbob]

Roy's mantra is "it's never the coil " but seeing if it is overheating is easy to check, by touch.

Sounds electrical to me so check the intregrity ( clean connections, no breaks or damage ) of :-
supply wire to the coil from the loom
low tension wire,white with black trace, coil to distributor
King lead, thick wire, top of coil to distributor cap
Remover distributor cap, any signs of cracks / tracking
main HT leads to spark plugs sound /
rotor arm
condenser ( could be packing up ) cheap enough to replace ( my money is on this )
Is the little low tension inside the distributor connectd to the lucar
connector still attached ?
Points not loose and a clean surface /

You weren't too generous oiling the distributor after it's winter lay up were you ?

If I've missed anything, someone please correct me.

Bob

[Stig]

My plan is to run it in the garage at the weekend until hot and see if I can repeat the fault, then set about diagnosis. Maybe a wet sponge on the coil will miraculously cure it, who knows. At least I can swap bits with the Minor to see if it makes any difference.

[faversham999]

Just like my car before the coil was replaced

[bmcecosse]

My money would be on the condenser heating up - It's 'never' the coil........

[chrisryder]

It's 'never' the coil........

except when it's the coil

[Chris Edgar]

Had the same problem many years ago & it was the coil.
Not easy to diagnose since there were still sparks at the plugs but presumably not good enough under compression.
Always had to wait until things cooled down & then engine would run again.
Nearly happened in the Dartford Tunnel...stuff of nightmares!

New coil solved it

[faversham999]

PS I changed the condenser and coil and points and rotor arm .It all right now so it must of been one of them .

[bmcecosse]

Put the old coil back on......and see.

[faversham999]

now have a spare coil

[Pikey]

I had an annoying misfire or cough when the pickup was warm after a good run. I replaced most of the ign to include leads, plugs, dist cap, rotor arm and eventually the coil. After the third coil (I suspected 2 duff coils to be honest, I think they were ballast ones), I seemed to have solved it, and the cough disappeared, until late autumn when the cough re-appeared again. The misfire went from an occasional cough to all out total stall on a hill and I managed to limp into a layby. A fellow mog helped out (thanks Godfrey) and we condemed my condensor, and after I changed it for a secondhand replacement it ran a dream and has ever since. I bet its your condensor packing up.

And in BM's words, its rarely the coil!

Steve

[chickenjohn]

my vote is on condensor as well! The coil tends to work or not work, i.e. faulty coil stops car dead. Intermittent suggests condensor.

Another thought, check for play in the distributor shaft, if the distributor is very worn this could be the cause of the problems described!

[MarkyB]

And in BM's words, its rarely the coil!

He says it's never the coil. Anyone else will say it's rare, but not unheard of.

[bmcecosse]

As I have explained before - I put the 'never' in inverted commas because obviously, just sometimes - it IS the coil. But as above - I've found they either work - or don't work - no in-between misfiring etc. Coil connections can be loose/corroded of course - well worth checking. Weak spark tends to be caused by either points gap - or dying condenser.......

[MarkyB]

Just pulling your chain .

[Stig]

And the answer was...

rotor arm


I tried another coil, then distributor cap & leads and it was still running rough and nearly stalling when idling with lights & fan on to give it some load. Swapped the rotor arm and it restarted quite happily and ran much more smoothly. I haven't had the courage/time to take it for a drive yet but I think that's the fix.
There's nothing visibly wrong with the old rotor arm and I can't measure any leakage on the multimeter (20Mohm range).

Anyone know a source of reputable rotor arms?

[MarkyB]

The Red high performance ones are said to be OK.

[chickenjohn]

Marky B, I have been asked to PM you concerning a related matter- watch your inbox!
cheers
John