Miss-fire on acceleration

[mike@thenook]

Just as I get everything working perfectly, I've now developed a miss-fire under low acceleration but more once the car has warmed up hardly at all when it's cold.
I thought initially it may a faulty Powerspark unit but replaced that with my new spare and it's exactly the same so, wondering if it could be the coil as I read this is sometimes a symptom of a defective coil?
The leads are all only a few thousand old, new plugs, dissy cap, rotor arm and the carbs are all in perfect tune.
On the move and sitting at idle there is no problem, just accelerating and only up to around 1,500 rpm max.

Can't think what else it may be...?

Cheers

[mole42]

Mine was behaving like that - turned out to be leaks around the carburetters. Although the engine ran perfectly when cold and idled just fine when hot, it would misfire under load when hot. Pulling the choke out while driving gave some relief. I sprayed oil onto the throttle spindle seals and it made an immediate improvement in the idling but it wasn’t until I changed the seals, and added a fibre washer under the centre hold-down stud that I could get the engine to behave properly in traffic. One other leak was the banjo for the brake servo vacuum which kept coming loose - Wellseal and Loctite cured that. It was perfectly well behaved up the hill at Prescott last Sunday.

[mike@thenook]

Cheers for that Richard, I'll give it a look..

[MandM]

I used a couple of dowety seals on the banjo bolt, instead of the copper washers, will check how many spare I have when I get back and send you a couple if you like

[mike@thenook]

Cheers, I'll take a look in the morning and let you know, appreciated

[DJT]

I had similar a while back. Turned out to be the resin filled Flamethrower coil. Misfire went away when I fitted an old, reliable Lucas Sport coil. Visited Martin at Distributor Doctor and he replaced the resin filled coil with an oil filled Flamethrower. Still effectively on test, but done about 1,000 miles so far without fault. He admitted that he had more warranty claims with the 1.5 ohm resin filled than with any other coil.

[richardthestag]

disconnect the vacuum advance and try again, if the miss fire goes away then it is likely that there is excess play between the fixed and rotating plates of the distributor baseplate.

Had this a few times now on Lucas 35D#8 distributors on Rover v8, as the vacuum starts to pull then the first thing the baseplate does is move slightly sideways before it starts to rotate. This on the Lucas system closes the airgap which creates a bugger of a misfire

[mike@thenook]

Well Incan say it's not the coil as i replaced the newer Lucas one with the older one, still the same.
Checked all the joints, gaskets, mixture, and still no difference but the baseplate idea sounds like one to check, thanks - something to do tomorrow
It's just really odd the way it only appears when it's warmed up and at low revs, so annoying.

[jbuckl]

Was asked to fit an electronic ignition to help with this recently.

The car already had luminition fitted.

The owner had a new powerspark to replace

During fitting I noticed the brake vacuum pipe was loose at the banjo…. Probably a likley cause of the issues …. Pops bangs etc.

tightened up the banjo bolt but pipe was still loose…. Braze had cracked all around.

took home, cleaned silver soldered and refitted.

all good after wards and after a run out.

also noticed the distributor was wobbling when the engine was running….

body casting broken …. Only 1 clamp bolt.


offered to swap distributor body casting for a new one.

the ones offered need very careful fitting…. They are not 100%…. Quite a few features are ‘out’

upon refitting no fire up…. The 3 week old powerspark had failed after transfer.

no receipt…. No refund

should have just fixed the brake servo pipe

[jbuckl]

Well Incan say it's not the coil as i replaced the newer Lucas one with the older one, still the same.
Checked all the joints, gaskets, mixture, and still no difference but the baseplate idea sounds like one to check, thanks - something to do tomorrow
It's just really odd the way it only appears when it's warmed up and at low revs, so annoying.

Coils are difficult to check on the bench.

They can tend to cause some intermittent problems if they still work. Heat and load effects can cause breakdown in continuity that can’t easily be measured.

A good power feed is essential too. Our looms and connections are 50 years old.

often connectors have been poorly remade with unsuitable spades etc.



Air leaks can be traced more easily with highly volatile spraying at and around suspected areas. (Joints & throttle spindles)

[richardthestag]

wrong rotor arm can make the cap wobble, I only have one bolt on my distributor baseplate and it doesn't wobble.

You cannot use a standard points rotor arm on a distributor converted to Electronic ignition. You need to use the later Rotor. Here is a short feature where a ham fisted gibbon helpfully points out the differences

https://youtu.be/nr1_jFssay8?feature=shared

While we are on about rotor arms, cheap "greenbox" typically (but not limited to, as many traders also knowingly selling this rubbish) ebay sourced rotors and caps are far too often the very poorest quality. The plastics used are often not suitable for high voltages in the HT system and will leak to earth. lift off your newly fitted cheap cap and look at the burn marks on the contact tips inside and you will understand about the tolerances and then look at the cheap and flimsy design of the rotor compared to, lets say, a used old stock Lucas original. New green boxed lucas is not like the red and black box lucas nor can it be assumed to be OE spec. Caveat Emptor etc

The only reliable source I have yet to find is Distributor Doctor

[mole42]

The only reliable source I have yet to find is Distributor Doctor

Agreed

[mike@thenook]

So bit of an update, went out on a 30 odd mile round trip to the Essex Young Farmers Show and while it hesitated a few times at low speeds on the way there, after leaving it for 5 hours in blistering sunshine (summer at last!) for the whole journey home right from the off including sitting in the "out jam" for around 15 minutes there was no hint of a problem, ran absolutely on song.
I read back on an old post in 2020 when Neil said he had exact similar problems owing to the white wire in the connector block under the dash kept creating a power cut and just wondering now if having had that connector cause me a big a problem a few weeks back, I though I'd sorted it but just maybe it still has a slight connectivity problem. Seems a bit of a coincidence....

Cheers

[richardthestag]

Your car may well be haunted

Is your a Mk2 stag with the pink / white Eureka ballast wire? if so don't use that for the 12v non-ballast ignition coil nor the electronic ignition module.

Run a nice new white wire from the back of the fuseboard, (there are a bunch of white wires to the back of the first 2 fuses) and direct to the the ignition coil +ive.

Alternatively find a white wire on from the ignition switch and splice into that.

The ballast wire is crimped to a white wire and bound into the loom somewhere above the heater unit, I had the crimp start to fail on my stag which caused a monster misfire which progressively got worse unit the car was undriveable. It would sit running in the drive all day long with no issues, get it on the road and the misfire would come in at around 5 miles and the car would be undriveable shortly after. give it an hour to cool down and the car would restart as if nothing had ever happened

[mike@thenook]

Thanks for this Richard, mine does have that pink/white wire but up until yesterday it hasn't been connected to the coil, it was cut off and the only +/ wire to the coil was the white/yellow one.
To see what happened I reconnected the ballast wire and apart from getting a slightly quicker fire up nothing changed. I'm running a Lucas DLB102 12 volt ballast coil but the original coil should have been a 6 volt I believe.
I do believe it's a fault in the wiring somewhere due the way the hesitance occurs, kind of a loose connector type of hesitancy.

So I think I need to take the ballast wire off again as with a 12 volt coil it will be serving no purpose..correct?

Cheers!