your Dragster is not running properly your spark plug should be
one of the first things you should check (especially on a two-stroke
like the Dragster). So which spark plugs should you use on a tuned 125 / 180?
Well, if you have a Dragster 125, then go with Italjet's
recommendation of a Champion RN2 C. But if you have a Dragster
180, then ignore the manual, because it lists the wrong plug!
It says you should use an NGK BR8HS. An '8' is too hot,
and in some cases can burn a hole in your piston. And the 'HS'
is too short, so it won't fit properly.
popular choice for tuned 125's / 180's is the NGK BR9ES
spark plug along with the NGK B95EGV for long runs or regular
motorway use, or the NGK B85EGV for shorter runs or town
For race use only you could go for an NGK B9EGV which is
a platinum race plug but this cuts out the indicator relay stopping
your indicator lights from working (hence race use only). Likewise
the NGK B9ES spark plug is not EMC certified which means
the plug can cause interference to nearby radio and TV signals
and will also cut out indicator relays.
You could also obtain an after-market spark plug cap that contains
a resistor element. The NGK range of resistor covers are
designed to give perfect noise suppression across all frequencies
whilst engine performance is not adversely affected.
Daft as it sounds some people have never changed a spark plug,
if you've never changed the spark plug before, it's very simple, first thing to
remember when fitting a new spark plug, make sure the engine is cold.
First remove the black plastic spark plug cover which is fastened to the frame with
three screws. Unplug the spark plug cable and using the spanner provided with your Dragster
unscrew the plug. When refitting a new plug make sure you engage
the threads properly and then tighten initially by hand and for final
tightening use the spanner provided.
For your information, NGK describe the various types of plug as
ES types - standard spark plugs with copper cored centre
electrodes for wide heat range. Copper's superior heat conductivity
dissipates the heat of combustion away from the firing end, preventing
hot spots that can lead to pre-ignition. Copper cored electrodes
also mean that longer insulator noses can be used to protect against
EG types - these plugs feature a smaller diameter centre
electrode tip made of conventional nickel alloy. The smaller diameter
centre electrode means the voltage required to produce a spark
is reduced. However as the tip is made of conventional nickel
alloy the service life is reduced and these plugs are best used
in applications where plugs are frequently changed.
EV types - these plugs have a smaller diameter centre electrode
(1.0mm) than the EG types which is made of Gold Palladium Alloy.
The smaller diameter centre electrode means the required voltage
is even lower.
EVX types - these plugs have an even smaller centre electrode
(0.8mm) than the V types, which is made of platinum. This combined
with a taper cut ground electrode has a lower required voltage
than the V types. This results in better ignitability along with
improved starting, idle stability and anti-fouling performance.
EGV types - these plugs have a centre electrode of precious
metal similar to the EV range. In addition, the insulator nose
is an improved design to allow better gas flow around the firing
end. The ground electrode is shorter and stronger, making the
EGV range ideal for the most severe racing applications.
Checking your spark plug is also the best visual evidence for
checking your fuel mix. If the mix is too lean it is harder to
notice, your motor will get good speeds and will run with virtually
no vibrations, however the engine can get very hot with the chance
of throwing a piston. Hence the only way of checking for a lean
mix is to take a close look at the spark plug. The theory goes
like this; if the spark plug is grey or very light in colour,
adjust your carburettor a little richer because the mix is too
lean. Generally racing cylinders will last longer if you adjust
your carb somewhat richer than needed for highest performance.
If you find that the spark plug is black or very dark in colour,
the fuel mix is too rich and needs to be made leaner.