Spark Plug Prob:

[johnbirchjar]

Hi guys,a wee problem I need some advice on.The Commander engine I have in the Classic frame just loves spark plugs ,(but only one, the O/S,the N/S one seems fine)the O/S only last about 800 to a 1000 miles ,no warning signs,it just starts to run on one cylinder/chamber,a couple of backfires and that's it.put a new plug in and its fires up immediatly.The carbs are about right(both exhausts are that nice very light brown heading towards grey colour after a long highspeed motorway blast,43/45mpg, oil(more or less) 400 miles to the pint.and the old girl fires up first stab of the button hot or cold and anywhere in-between, so me thinks the prob is almost definitely 'leclic.
I have always used NGKC8E plugs,so,apart from the "Discharge" plugs are there any others I could try?
I did a bit of an experiment this morning,got the duff plug,tested it for spark with the N/S plug lead, big fat spark,put it in the N/S chamber,it fired up straight away(cold engine)lasted about 5 seconds,then ran on one,changed back to the plug that came out,back to both chamber's.any thoughts?J.B.

[David Rodgers]

Hi John

Try swapping the plugs over rather than fitting a new one straight away, to see if it cuts out on the other rotor. If so it's the plug!
If it fails on the original rotor O/S then it's possibly something else.
I had this once and a new pair of plugs cured it.

Regards Dave R

[johnbirchjar]

Done that,and it did .Three new plugs,and it happened to all of them ,so what is causing the plugs to "break down"but only on one side?could it be the Coil punching out to much power and cooking the plug?(I'm clutching at straws here,'cos I've never heard of this problem before,cry) I suppose I could swop the coils over and see if the problem transfers to the other pot ,that way I would know where the prob: was ,
I expect there is a way I can test the output of a coil with a Multimetre?(a tad quicker than having to ride 800 to a thousand miles to test a theory )any thoughts on alternative plugs?J.B.

[johnbirchjar]

I've had a bit of a "surf" and it seems that one can test coils to see if they have a problem immediately(engine not firing or firing intermittently) to test for the coils "breaking down"but not how to test for "cooking of plugs"after quite a few miles(as in my case ) none the less, I will carry out the tests and report anon,J.B.

[johnbirchjar]

Having carried out the tests, the readings on both Coils seem to be within the parameters suggested on the "Net".
So I have decided to swap the coils over(o/side to n/side) and see which plug breaks down(if any ,)I will of course report on any developments(it may be a while,if things run true to form about however long it takes me to cover 800+ miles )ride safe,J.B.