Spark plugs

The plug is matched to the engine, the ignition system should not be a big issue. BPR8ES  the R indicates there is a resistor in the plug. Fine to reduce interference with the neighbours TV but not recommended especially if you have resistive caps. Champion or NGK is your choice. But the right one for the engine.

I've been using Champion N7Ys (Now N7YC) in my 850 for about forty years. I change them occasionally if the plating is looking tatty.

John......please be very careful where you purchase your plugs from.  Around 4 years ago, one of the TV 'consumer' programmes highlighted a 'fake' product scam that was doing the rounds at the time. The item in question being dodgy spark plugs bought on-line or at auto-jumbles.  Top of the consumer crap being most bikers two favourite choices of plug.  These specials being printed with temperature codes a million miles from the actuality. Experts were able to differentiate the real plugs from the fakes by checking out the plug box labelling, text on the plug itself and the shape of the electrodes. Most of the rest of us would probably struggle.

Purchase your replacement parts at a well-known spares outlet and don't be tempted to put price before quality.  

I use Denso plugs from RGM, I’ve had problems with Champions previously.

Best regards, Al.

If the engine is set up for 'racing' ie high-revs, hot working engine, modestly well tuned and used hard then a 'town-soft plug' could cause a miss fire and eventually cause overheating and damaged engine. The obverse of this is a 'racing' hot plug used in town driving, pottering about it will foul up and also miss-fire. But the later will be a nuisance while the former could cause damage.

There are 2 pazon EI families, an analogue one and a digital one. Analogue do not need resistor plugs or resistor caps but will cope with one resistor, digital need either resistor plugs or resistor caps not both. Same rules for the Boyer etc, Trispark are all digital, Wassell are all analogue.

… the Green Spark Plug company website has lots of useful info: https://www.gsparkplug.com/technical-information

(They'll also sell you some plugs and lots of other stuff — usual disclaimer.)

On the NGK website is some info about the fake plugs which is quite common. Another thing I've read is that the ceramics in the insulator nowadays is different to work better with modern engines. Been told that NGK plugs made in France are more prone to oiling than those made in Japan.

All from internet, so it must be true!?!

... is that the ceramic on the nose of the plug is not glazed as it used to be so that carbon is almost impossible to remove. But again internet gossip so may or may not be true.

I would think the BPR8ES plugs are too cold and may cause misfiring.

BPR7ES or my choice BPR6ES are in the correct range.

Dave

do not seem to be as good as they used to be.  Recently I broke a spark plug, so bought a new pair of BP6ES plugs from a local main street motor factor.  I  got a continuous stuttering misfire.  I refitted the surviving old plug and an old B6ES cadged from a fellow rider, and smooth running resumed. 

Recently bought Champion plugs from a reputable supplier. Bike ran badly and put NGKs back in and all OK !

I had a long conversation with Stan Dibben when he launched his book on spark plugs (Shepton Mallet some years ago).  He convinced me that they were top rated plugs  I had used Denso and Champions up to then.  Then a new machine came into the fold and NGKs were fitted.  there were pops and bangs as I got the carbs eased in and then I left it till the next weekend. 

Would it start?  I tried and upset everything I had done previous and ended up kicking myself to a standstill. No go.   I eventually reverted to some old N7 plugs as the two new were wet,  and I got an instant reaction.   A bit of adjustment and tweaking and she came on as sweet as.   The wet plugs were dried in the oven and put on shelf, never to be used again...

Someone probably has the inverse of this story but that was my introduction to NGK... No Good  Kickstarting.

Cheers

Jon

I'm glad the Spark plug subject is again topical, as I was about to seek advice. My MKIII I've owned 20yrs but not yet worn out a back tyre.  About 6yrs ago started misfiring or wouldn't  start. Fitted new plugs, problem solved, for the time being.  Then the mileage between "plug failure" became less.

I had the Boyer tested, OK and have been through many pairs of NGK, Bosch and Champion, correct grades. Within the last 12 months a 50 mile ride then symptoms until where I am now,  new plugs a 12ml ride then symptoms.  Next day brushed and gapped the plugs to 25thou and went off down the road misfiring, became worse, engine stopped on the side of the road. I fitted another set of new plugs from my pocket.  Road back home, 1 mile, as the bike should, no symptoms, running great.

Points are: 1.the running time to symptoms has decreased. 2. What is happening to the plugs to render them permanently unusable.  3. There is a faint background ign light glimmer (engine running) could just be the assimilator or is the alternator allowing the battery to run low and starve the Boyer, I'll have to fit new plugs to check alternator?

So where I am now is process of elimination and replace the whole ign system leaving the most expensive part til last.

Any tips greatly accepted.

The first thing to replace on any Commando fitted with a Boyer is the lead from the pickup to the black box. They break regularly within the insulation and make and break as the engine shakes...I'd dismantle all connectors and check and clean.

They say that once modern plugs foul, they're less likely to recover. It may be that the fouling plugs are a symptom of problems elsewhere.

I had plug troubles for a couple of years on my 99 . Improved with a change of needle jet ( a 1055 instead of a 106  plus running the pilot weaker than ideal for good starting.  Then I dug out an old (very old !) set of N5's  and  things have been fine , they soot up a bit when cold but clean up once warm. Picked up some NOS  KLG plugs ( with pink shiney  insulators!)  and they are just as good.  I suspect that if you have a very clean running engine that warms up fast then you will think we are  all paranoid ,  about modern plugs , but I am sure some makes  are now  not up to the job of coping with our old dirty running  motors.

What do your plugs look like when they pack up Micheal?

Plugs look normal Alan except recently I don't get far at all and fiddle with the choke to keep going which shows a sooty plug of course.  Checked lead to Boyer box, no breaks. Resistance readings on both coils identical and correct.  I know plugs may not perform under compression but outside they give a nice blue spark.

Boyer timing is correct, white spot visable at 28btdc. I saw a video an American sorting a Triumph 120 so check engine earth, dump the zener and despite Boyer being given a clean bill years ago I may update to mk4.

Boyer timing is correct, white spot visable at 28btdc.

That is the get you running position and can result in the actual spark being up to 8 degrees out depending on where all the electronic components are within their tolerance range. Hence why in the Boyer instructions they recommend the timing is checked with a strobe.

I once changed the boyer box alone on a bike that had been strobed for 31 degrees advanced. and the pipes went blue as soon as the bike started as the new box pulled the timing to be under advanced. When I re-strobed it I had to pull the rotor off its taper to get the timing back in range.