SPARK PLUGS

If 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.
 
A 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 riding.
 
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 follows:
 
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 fouling.
 
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.

CARB TIPS

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.