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Collection, Preservation and Display of Old Lawn Mowers

Spark Plugs

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I was using my 2 stroke Qualcast 16 lawnmower with a Champion D16 plug fitted all last summer to cut the grass.  The plug was bought new in May of last year and the mowing takes about an hours continuous running each week.  Last week the plug seemed to have given up.  On testing it seems to spark for a while then stop.  Is this to be expected if a plug is failing and should it fail after only one year's use?  The plug is black in colour.  Should it be black or brown with a 2 stroke engine.  Many thanks for any help/advice or comments. 

Forums

gtc Wed, 26/04/2017

An oil fouled plug usually indicates too much or the wrong type of oil in the mixture, and a fouled plug won't spark correctly if at all.

A dry black plug would usually indicate a too-rich air-fuel mixture. Any deposits on the central electrode tend to break down the required insulation and weaken the spark at the tip.

In the old days of leaded petrol a brown plug was the ideal, and white plug indicated a too-lean air-fuel mixture.

 

 

hillsider Wed, 26/04/2017

Might seem an obvious thing to suggest but have you tried another spark plug? If so what was the result. 

wristpin Wed, 26/04/2017

I cant lay my hands on the post on another forum but the gist was that the centre insulator of old spark plugs used to be glazed and modern versions are not and become contaminated. ( hope that I have got that the right way round)! I have a similar issue with NGK A6 plugs in my Dennis ( four stroke) . A new plug works fine the first time out but then refuses to fire the engine the next time round. 

In days gone by the village garage would have a Champion plug tester which would be connected to a compressed air source to simulate the working conditions in the engine's cylinders. It also incorporated a mini sand blaster to clean the interior of the plug. These days this is frowned upon as there is the possibility of small abrasive particles being left in the plug and then released into the cylinder .

That said I have cleaned plugs in that way in my blast cabinet using glass bead media - followed by a good blast out with solvent and compressed air - and obtained a second life from " failed " plugs.

Hope that this throws some light on your problem.

 

DanAcre Wed, 26/04/2017

Champion plug says it all in 25yrs of cars and engines I've never had a reliable set and have always failed early I now and for some time only used NGK Bosch or Beru plugs change the plug out and re-gap re check spark :) then take it from there

DanAcre Wed, 26/04/2017

I've wondered why they removed the glazing the first reasons I can think of are cost/ wanting them to fail early or running temps and failing on modern engines

didnt they used to sell a plug cleaner that powered from the cigarette lighter  

pyneapplechunks Wed, 26/04/2017

I have tried another Champion D16 spark plug and was able to get the mower working but it seems rather a short life span for a plug.  I assume the plug will be black and not brown as it's a 2 stroke.  Is this correct?  The mixture I am using is Millers Classic CM 2T SAE 40 oil with standard petrol in the proportions originally recommended.