Elusive missing problem

[NoviceM]

I have recently acquired a 1098 1970 traveler.
Runs fine except.....annoying engine miss when labouring, just before changing down say from 4th to 3rd gear.
When engine is running freely on flat etc, no problem, missing only appears when engine is lightly laboured.
I have sequentially changed all the usual suspects, plugs, leads, coil ( points and capacitor were changed a few months ago).
Mixture looks to me to be about right, plug centre electrode nice light chocolate colour.
Any ideas will ve very welcome, I am out of ideas.

[panky]

A lot of the condensers available today are pretty rubbish, I would try replacing it and go from there.

[simmitc]

For other ideas, see viewtopic.php?t=49906&hilit=average+misfire

I also found one that "everyone" agreed was a misfire and even the engine was changed for the problem to remain. Solution: a worn UJ on the propshaft, at certain speeds/loads the imbalance produced juddering just like a genuine misfire.

[NoviceM]

Many thanks for useful suggestions,.

[myoldjalopy]

'Novice M' - a couple of possibilities you have not mentioned include the dizzy cap and the rotor arm - maybe worth checking those out.......

[mowogg]

Have you checked the ignition timing? It could be too advanced

[NoviceM]

New dist cap and rotor arm already changed. I will retard ignition a little and check if any difference. Could running too lean cause similar problem, new plug centre elecrode very white, old plugs were cream to chocolate before I routinely changed them, same type of plugs.

[svenedin]

New dist cap and rotor arm already changed. I will retard ignition a little and check if any difference. Could running too lean cause similar problem, new plug centre elecrode very white, old plugs were cream to chocolate before I routinely changed them, same type of plugs.

Running too lean will also cause the engine to run hot. Check your valve clearances. Are all the plugs showing a lean mixture or just one?

[NoviceM]

Thanks for advice, I think I have found the fault....the replacement points set I fitted.....were faulty, the movable arm binding on its pivot at random intervals.
Refitted old set of points...problem fixed !.

A secondary issue I have is....plug colour suggest mixture is lean. Lifting pin causes engine speed to faulter....but, on tickover, exhaust smells rich. Not sure what this conflicting info is telling me ?
Cheers
Garry

[les]

I had the same issue with points binding on pivot, despite being bought from a reputable supplier.

[svenedin]

I recommend contact sets sold under the “Remax” brand or buy from Distributor Doctor (he only sells the best stuff). NOS Lucas contact sets are excellent if you can find them but they will need the contact pads very thoroughly cleaned as they are likely to be oxidised from long term storage. A very thin smear of silicone grease on the pivot post is not a bad idea (it does not conduct electricity).

Stephen

[les]

Maybe the best stuff had an intruder !