Navigator Spark Plug Recommendations

Spark plugs have changed a bit since those recomendations.Modern  vehicles are now lean burn and mixtures computer controled . This has meant that some makers no longer bother to make plugs that are able to resist much  soot contamination and insulators have become more porous and are not so capable of self cleaning. Our old bikes however continue to soot up plugs with our use of choke ,bad mixtures and poor oil rings  . You may find you need to go to an N5 to avoid ignition issues when just pootling around. However there are dangers in running a softer plug . A hot running engine ,weak mixture or over advanced ignition  may overheat the plug and cause damage to a piston .  Its a bit of a dilemma. I continue to use old vintage plugs that i can clean with solvent or a good burst of power. 

I run an Electra with Pazon. 

Agree with Robert about the wisdom of running cooler grade of plug.

After trying N4c and NGK equivalent, I have settled on N3c and it seems fine. I always get instant starting and good running. But,.... I have some years experience of the best relationships between ambient temp, engine temp, tickler, choke and throttle.

On removal the N3c always looks a bit sooty, indicating a hotter grade might be better, but it just does me fine. I do plenty of pottering and sometimes longer runs at 60mph, up hills and down dales.

Let's see what other lightweight riders use. 

Peter

Sorry, but I just had to laugh at Peters 'I do plenty of pottering and sometimes longer runs at 60mph'

This is the man that is riding his Electra to the Rally in Spain...

Peters advice is counter to what i have posted. And it shows how our bikes ,the way they are set up ,how we ride them , and what make of plugs we use will dictate what works best in our bike.Peters bike must indeed  be very well set up to tollerate N3 plugs. The same plugs in my 99 would have me  kicking my way to a heart attack. If i was going for another 6 lap blast around Brands (most fun I had for years!)  I would fit something harder (colder) than the N5's I currently use  for local pottering around. Probably N4 or KLG FE 100  . Remember them? A blast from the past.

I would start with the N4 's.  Plug caps ,i use bosch 5 ohm in coil bikes and  zero resistance with a mag. Test any other caps with an ohm meter and dont be surprised if they go to infinity and somehow still manage to run (badly).

For the record the change to12V and Electronic ignition will NOT alter the grade of Sparkplug. The spark plug grade is dependant on the temp in the engine, which as far as we are concerned is down to the state of tune and usage, ie do you pootle or thrash. In our usage of bikes/engines then always start at the manufacturers recommended, if then you have a problem, refer to the plug manufacturers data.

My 650 Manxman started life in 2009 with a Magneto and Champion N4 spark plugs set at 18 to 20 thou gaps. Four years ago, I changed the magneto for a Wassell Electronic Ignition set-up and was advised to set the plug gap at 22 to 24 thou. Both systems worked fine with new N4 plugs.

The Magneto fed plugs needed a clean and re-gapping every 1000 miles whereas the Wassell system allowed three times that distance before cold starting became difficult.

AJD swears that the latest, very expensive, triple electrode plugsare the way to go. Claiming they give easy starting, good idlling and long intervals between needing a clean.

The answer to Phil is very easy, the Magneto gives less power/voltage than the electronic (Wassell, in this case) therefore a smaller plug gap and sooner fouling. But of course going electronic puts one in greater demand for the battery and its charging, So beware of trying to run electronic ignition with Dynamo battery charging (not the case with the Manxman as alternator). We are now well off top-pick of Lightweight plugs!

Most plug issues are caused by oil contamination or carb richness. Wet sumping , extended running in due to oils not allowing proper bedding in . overoiling with uprated pumps ,valve guide clearances and lack of seals,too thin oil for the design (  my 99  on 10/40 !)  ,poor oil control rings etc. Carb issues ,wear of needle jet ,fuel level too high. loose pilot jet,.needle too high , slide cutaway too small ,dirt on float needle seat, wrong (2 stroke  T marked  ) needle jet , Pattern parts etc.  Slightly retarded timing not allowing plug to reach full temps  and then there are  weak mixture problems and over advanced ignition  to damage plugs ,or just poor electrics  to cause fouling ,   Enough !!.

I thrash my poor little Navvi within an inch of its life (mostly), and had a local expert look at my plugs recently. I'm running the 170 main jet as the book says, and he thinks I should go up a size. Raising the needle is not what he is after.

My plugs are Champion N7Y, which have a slightly longer reach. They are sooty on the outside, heading to white & clean in the centre.

I use E5 fuel.

A   light ring of soot round the mouth of the plug is normally something to aim for. There is something to be said for a smaller engine doing proper work.