My 1959 magneto Dommie has been running fine until this week when I experienced slight stuttering and loss of power at low speed. Removed right hand plug found it very sooty, dry carbon and no oil evident. The left hand plug was perfect light brown. Changed right hand plug and after 10 miles or so the same stuttering occurred, this plug had also become badly carboned and there was slight popping in the RH silencer at tick over. All classic signs of a rich mixture, but on one side only! Single carb and running with Champion N5Cs. Carb was new six years ago and is clean as a whistle. Did 300m in the Dales two weeks ago with no problems.
Today I have checked the carb, ignition timing, points gap, cylinder compression and valve clearances, all spot on. When riding with others no smoke was reported from either exhaust.
I'm now looking for some pointers as to what the problem is, any advice gratefully received.
I wonder if you have a loose…
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Only one variable….
From your description the motor sounds in good order. Fuelling is symmetrical, mechanical requirements met. So the only area left is ignition. You may well be operating on low limits of points opening or there is a component breaking down on your right hand circuit.
How is the power when you are on the open road?
Jon
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I agree with Jonathan, most…
I agree with Jonathan, most likely to be an ignition component on one side . Lead, plug cap ,plug.pick up on mag. Definately not carb.
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Sounds Like Electrical
My first thought was similar to Dave above......a duff inlet guide, which it still might be but the hint of a miss-fire leads towards a Magneto issue.
Check the pick-ups for a stuck or broken brush.
Checkout the magneto points gap is correct for both pick-ups. 12 to 15 thou. Worn bearings will throw this out on one side.
Finally replace the plugs and check the leads and plug caps are doing what they should be doing.
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Soot (Dross alert)
Some sound advice for you above, Barry. Ignition almost certainly the issue, other than valve guide wear and ring damage. N5c a good choice of plug.
Incidentally, I'm pleased to see that you have identified your plug soot as carbon. For some reason this gets confused with carbon dioxide the gas of life. The plug soot you can do without.
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Thanks for replies
Thanks for all the replies, very helpful and much appreciated, I'm going to follow them up today. Regarding the mag, I did have this fully checked out prior to my Dales trip, it also had new HT leads and plug caps fitted. So first of all I am going to swap the HT leads etc over and see if the fouling of the plug follows.
Regarding loose valve guides, I assume this would lead to excess oil entering the combustion space with oil deposit on plug and smoky exhaust, which I don't have. However if the above doesn't work I'll have the head off for a look.
Regarding power on the open road, this did not seem to be affected, the stuttering was happening at low speed and on pulling away from junctions.
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I wonder if you have a loose valve guide? Or just possibly the manifold gasket leaks on one side? I don't understand why they'd have the effect you describe but it must be something that's different between the two sides but not obvious from the tests you've done.