Old misfire - again

[tony]

Don't think it matters much today. Higher fuel octanes makes the whole thing academic anyway.
Tony.

[Clifford Pope]

Can you explain that - are you saying it doesn't matter what advance we use - anywhere between 10 degrees and TDC will do?

When I had a Triumph with a Mk1 engine it was absolutely critical to within a degree - too advanced caused pinking, a few degrees too retarded completely took the edge off performance.

[Clifford Pope]

I've fitted new spark plugs, checked alternator output 13.8 volts, re-set the carburettors, and tried again.
Initially all was well - it fired instantly, ran nicely at idle, revved up smoothly - for about 5 seconds. Then it became more burbly and uneven, misfiring became worse, sounding as if it might be going to backfire. It stopped idling smoothly, spluttered, and finally stalled.
I fiddled with things aimlessly for a few seconds, and tried again. Initially it was perfect, but again rapidly declined.

Tried a different coil - no difference.
Managed to check timing - it had drifted off about 10 degrees, but resetting made no difference.

I'm suspecting the new distributor and Acuspark unit now - it doesn't actually seem very well made. The cap doesn't locate all that positively, has a sort of plasticy lightweight look. Perhaps it's not a genuine one? I've been reading revues and they either seem to give no end of very similar problems, or last for ever with no problems. What do other people use?

[johnnydog]

I think you will have to go back to basics on this one. Assuming that all the fuel components are clean and clear of sediment or rust (tank, fuel lines, pump, fuel bowls and all connections are good), and that the carbs are set up correctly (not particularly the mixture at this point, but the linkages operating correctly / simultaneously, the pistons are clean and free moving), then it must be back to the ignition side of things.
If you are like me, you must have 'stocks' of known good components, such as good used plug leads, rotor arms combined with used distributors etc etc , good old 'genuine old stock' coils (suitable for your particular car / ignition depending whether you need a ballast), condensers and points.
I'd be tempted to remove all the components and take it back to as near original with good known used parts and eliminate individually from there. Otherwise continually changing random parts will just result in you chasing your tail.
What type of air filter / collector box set up do you have on the car?
I get why modern parts are fitted for supposidly better reliabllity or performance, but none of my cars are any different from standard, none with electronic ignition and the ones on the road all start / fire up and run well without issue. Only one has a red rotor arm (some red rotor arms don't seem to fit very well on the centre shaft, so in that case I have retained a genuine old Lucas rotor arm).
I think that's all you can do from here on - go back to the original and take it from there. My gut feeling is still on the rotor arm though....

[tony]

Sorry Clifford,
Didn't mean for you to take my remark literally. My TC runs electronic ignition and runs on 98 octane fuel. I'll start of timing it around 8 to 10 degrees BTDC and then tune out the pinking as necessary so never end up as the book says. All I meant was that with modern fuels Its not the same as it was 40 years ago.
Tony.

[Clifford Pope]

If only to vindicate the Acuspark I've refitted the old distributor, but I firstly took it apart and filed and ground the outer side of the condenser slot. It now sits comfortably with about 1mm clearance from the cam lobes.
I've also ground down the securing screw so that there is space for it to sit properly. Previously, tightening it shifted the condenser position and tilted it upwards slightly. The screw then worked loose.
Finally the hole in the securing lug on the end of the condenser was slightly wrong, not centred over the hole in the plate.
All the CW condensers I tried were like this, so it seems the distributor plate came from a different car that was meant to use a slimmer condenser?

Anyway, I tried starting the car this morning, and it fired up instantly and runs perfectly. Not a trace of a misfire!

So it appears that the original fault was the slot in the distributor plate being wrong, and the Acuspark unit has failed in a very short time - perhaps half an hour of running. I have checked the battery voltage on running - 13.7 volts - so not excessive. Coil, and the previous one, 3.5 ohms. I've found a lot of comments on the Acuspark and Petronix. Opinion seemes split between half thinking they are marvelous, and half finding them unreliable and fail quickly. One forum correspondent recommended carying a spare distributor for quick replacement if/when it failed.

I need a longer test now to see if it really lasts.

[Charles H]

Pleased you seem to have got to the bottom of it!

[Firewatcher]

Hi Clifford,
Fingers crossed then. May be of interest if that hasn't put you off electronic ignition, I fitted the Powerspark electronic ignition kit about seven years ago. I was a bit sceptical at first, so kept a set of points and condenser in the glove compartment just in case. I use the car every day and it sits outside, but have never had any trouble, so am entirely happy with it. Cost about £35 and it is simple to fit in a standard distributor (and change back if you need.)
Pete

[Clifford Pope]

Fingers crossed indeed - I've been at this point before.
I wasn't against electronic ignition before this episode - I'd had Luminition in two other cars, a Triumph Mk1 and a Volvo 240, and both lasted for years with no attention. But it's very expensive now, as is 123.

That said, I replaced the worn out distributor on my 1949 Ferguson tractor with an old Morris Minor spare that happened to fit, in 1985.
The tractor's run perfectly since then. I haven't had to replace anything apart from a rare oil change.

[Clifford Pope]

I've just made the interesting discovery that there are two kinds of ignition points available for the 45D distributor.
The kind I hate, with the spring rather feebly sitting in a plastc shoe, and the condenser and feed wire joined by a bit of metal that is just a press-fit in the doubled-over end of the spring, is normally listed for the 2500 Mk2 S.
But GCS 101, listed for the 2000 Mk2 and 2.5 PI Mk2, has a different plate with a longer threaded securing post, and the old attachment method of a loop of the spring secured by a pair of stepped plastic bushes, usually joined by a thin plastic tie so they stay together and don't get lost.

The condenser GSC 111, likewise listed for the Mk 2 2000 and 2.5 PI, clamps on top. The longer post accommodates the thickness of the wire and condenser endings, and the plastic washer bits. This seems to me to be a much better arrangement. The spring is properly attached and can't jump out of its shoe.

Further, I've discovered that there is a special clip that enables fitment of the later two-part condenser/supply cable (GCS 109), in the form of a doubled over clip that clamps the condenser fitting securely, and has a large hole at the other end that fits on the threaded post clamped to the end of spring.

I only discovered this when I got a secondhand distributor from Chris Witor, which was listed as for the 2500 S, and found the alternative superior kind of points set up. It also has a slot in the correct place to locate the condenser so that it doesn't rub on the rotor cam, and an older condenser that has a much more solid fixing lug that has the hole in the right place.
It also has the special little clip, which I can't find listed anywhere.