Ignition question

[Buckles]

I recently bought a Gunson Colortune. Something I have been meaning to do for a long time. I am confident I have adjusted the mixture more accurately and found it easy to use.
While using the Colortune and watching the colour of the flame at idle there is a periodic but short interruption to the firing of the 'plug' with some regularity. The interruption is a microsecond but it is clearly there. The car is performing properly in all aspects as far as I am concerned. I am just interested in the significance of this misfiring. As you rev the engine with the colortune operating the periodic misfire is less often but still there. As I said before the engine does not sound to be misfiring it is just a visual thing.
I have standard points and coil and the dwell is within the recommended range.
any suggestions would be appreciated.
Ian Buckley
TC 4083
South Australia

[Steve Simmons]

Just a thought, but maybe swap the plug wires with new ones?

[Buckles]

Steve, thanks I didn't think of that. It would be interesting to watch this sparking with Petronix or similar fitted to see if it is more even. From memory I think they claim smoother idle.

[i.thomson]

I have never been too happy with the colourtune as when adjusting the mixture I never seem to get a clear colour without flashes of the other. I find this makes setting the mixture difficult. I am not talking of "missing" here Ian, as you are, but as it always seems to go OK afterwards I ignore it. The other problem is seeing the colour at all on the sunny days when I want to do such work, a problem shared with using the strobe light, a job often done at the same time.

Ian

[Rick Waters]

I well remember my MG-owning uncle, when he told me: "Carburetor is a French word. It means 'Leave it alone'"

I use a Unisyn to sync the carbs, then the well-known "adjust the jets and lift the piston" technique to set the idle mixture. I check the plug insulators for colour, and if all is well, leave it alone after that. When my TC is running beautifully, I do notice that if I stand at the back, and listen to the exhaust note whilst the car is idling, it can be somewhat uneven.

Much more interesting to listen to than some boring perfectly even idle exhaust note, I think.

[Steve Simmons]

I've never heard an M.G. of any type that didn't have an intermittent exhaust note at idle. The 6-cylinders seem to be much smoother, but the 4-bangers are always noticeably lumpy. I've been told it's just an inefficiency in the old design.

[Buckles]

The comments about uneven idling are interesting. My cars are the same, despite the performance being otherwise OK. It is good to know others sound the same or similar. I will sleep better now...

Ian, yes there are flashes of orange intermingled with what I otherwise think is the right colour. I guess I have just tried to find the best average. The plugs are cleaner now especially around the electrodes but still black further away. Making adjustments based on plug colour is much harder than years ago when we had leaded petrol. Plus my exhaust pipes always seem to be black. This doesn't apply to modern engines of course, but we are saddled with making our cars perform as well as we can with modern fuel. It would be interesting to know how different fuels are between Australia, the UK and the US. I think we use a different octane rating system than the UK but there is probably more to the issues than just the octane.

The Colortune is hard to see if there is too much light nearby. I didn't have much success with the tube and reflector for watching the colour from the carburettor side of the engine. I used the bottom half of the tube and looked into it while I kept opening and closing each side of the TC bonnet. Perhaps this is an incentive to make or buy those devices for holing both sides of the bonnet open.

Ian

[Warmuthb]

I've never been sure about the distinction of the exhaust note given in the manuals...irregular...splashy....rhythmic ..or some such. Always have a dark tailpipe due, I think to the ethanol gas. Adjusted to perfection, car runs good...all is well. Can't worry about it- just drive it.
Brian