Atlas Misfiring

Jim - Is one cylinder worse than the other ? if so you can swap the plug leads to the plugs so the coils are now connected to the opposite coil.  This is only possible if you're using the wasted spark connection that is usual for the Boyer equipment.  So if the misfire has moved to the other cylinder you can eliminate certain components. The Boyer equipment does give problems if the battery voltage is not high enough - so check the alternator and rectifier are providing sufficient charging. Does the bike tick-over evenly ?  or is it misfiring on tick-over.  Cheers for now, Howard

Hi Jim. Have you checked the condition of your battery? You need a really good 10 volts at least for a Boyer Mk4 unit and even higher voltage for a Mk3 unit.

Also, I had a really bad continuous misfire while out on a ride. It turned out that I had a loose connection at one  ammeter terminal. Are all of your connections good?

Good luck

Regards  Tony

I recently had difficulty in starting my Commando. Last year I noticed that it took a few more kicks to start and this year, after the winter lay up, it was really hard to start and I had  a few kick backs so I decided to change the ignition for a Pazon system.

The commando now starts first time and runs so much better with the new system fitted. Before I consigned the Boyer to the Norton parts shelf, I looked at the Boyer magnetic rotor and noticed that one of the magnets had just about lost all magnetism, the other magnet was better but very weak, perhaps this was due to the system being 30 years old and the magnets lose their effectiveness over time. Perhaps yours might have the same issue. It is difficult to check the efficiency of the rotor's magnets in situ, you may need to remove the rotor. Another quick test for sparks is to wave a magnet over the transformer pick ups, this tests for the system producing sparks easily. 

No idea why one plug is blacker than the other side, perhaps carburation issues.

Regards Steve.

  When you say "the same", is the misfire on the same cylinder?

I'd try a new set of plugs as my first option.

Spark plugs are a very subjective topic.

I used to run Champion N5's in my 1965 650SS and had intermittent missing and black carbon build up.

I was advised to change to one grade hotter by a spark plug expert because of modern fuel is designed for fuel injection.  The change made all the difference. Steady idle and responsive throttle across the rev range.

Other riders will swear by NGK. Experiment and see if you get a benefit. Plugs are still cheap.

Hello Jim, despite the Boyer being a wasted-spark system whereby both plugs fire together and the difference in plug colour could be a bit of a red-herring. The Boyer stator is well known for suffering wiring failure after a few years. Assuming the ignition timing is correct, mark the stator position with a scribe or marker pen and remove it and carefully check the reverse side, there are two wires connected to the circuit board. Check that these are secure and also check that the actual wires are not broken internally - heat and a generally 'hostile' environment in which the rotor/stator resides doesn't do the components any favours. These faults are well-known for causing poor starting, misfires etc. 

Good luck.

It is easy to check the pickup plate for miss-fire. Get the engine started. Having taken off the pickup cover. then wiggle the wires. If there is any problems it will very soon show up. If the pickup wires are broken it can be inside the insulation, so you can't see a thing but wiggling the wires soon shows it up.

Hi Ian, what actual plug did you use, N6?

I remember having a shocking misfire on a 1972 125 single Honda which I had as a (just) 17 year-old and I was frantic to sort it before taking my test, I had serviced it and fitted a new plug, which I replaced again in case it was duff, eventually in desperation I refitted the very old rusty plug which had been in it when I got it  and it ran perfectly, it turned out the manual had transposed the UK and Canadian spec plug numbers (it was a single suffix letter different, my friends manual had a little slip of paper glued in) and with a new plug of correct type it ran faultlessly for the rest of the time I had it.

That was a very valuable lesson for me that the slightest difference in plugs can have a big effect

Yes Niall, I now use Champion N6's. (New old stock items). Champion plugs are hard to get down here in Oz these days.

I converted my last two Norton Atlas bikes to wearing Commando cylinder heads. Which brought about the quandary of which spark plugs to use.  N5 or N7Y?  As I had electronic ignition with a twin output coil, I opted for the N7Y.  The engines were also fitted with Commando pistons of around 8.9 to 1 compression plus slightly retarded ignition. 

This set-up worked fine and never caused any problems unless the battery got low on volts. But I could still do with an answer as to which plug would be best for that engine?

Meanwhile .....while back in lateral thinking mode I think that Jim needs to be looking beyond spark plugs for the cause of his mis-fire.  Twin carbs with one badly re-assembled is a possibility. If the Jet blocks have different underside washers this will cause problems.

Also worth visiting are the pushrods ends in case one has worked loose. A sticking valve due to a guide problem would be next on my check list and lastly air leaks in the intake plumbing.

Jim,

I've just been checking a misfire on my 1969 Mercury and found that the 2MC capacitor is faulty.  When this was working it was masking another problem i.e. the charging system.  If your Atlas is fitted with a 2MC capacitor It may be worth disconnecting it and see if the engine runs better.

These capacitors do have a shelf life, so will need replacing at some stage.  I replaced the original in 2012 with an RGM equivalent, so it's lasted 10 years.

Too much fuel leaves the plug  a matt fluffy black. If its oil its more shiney smooth black.