Vespa Maintenance Guide

Rolling Your Own Spark Plug Wire

If your bike ever becomes really hard to start or a pain to keep running, it may be caused by a weak spark. Other than replacing the sparkplug, there are a few other measures that may help your bike start and run better. One of them is replacing the sparkplug wire. This high voltage wire rots over time and causes a resistance to build up between the CDI and the Spark plug. Usually the symptoms will be misfiring (popping from the exhaust), hard starting and sudden motor die outs. Replacing these parts is good yearly maintenance. Do this job only after you replace the plug and check the carb over. You will need to go to a motorcycle shop and get about 20" of stranded spark plug wire as well as a plug head (you may as well replace it too). The job costs about ten dollars and takes less than 5 minutes.

Tools & Parts Needed
20 inches of Stranded 18AWG Sparkplug Wire
A good set of wire cutters
A plug cap kit (includes a cap and two pices of rubber)
A pair of pliers
Sparkplug Wrench

The Carb Box Step 1

A picture of the goodies you need. Costs about ten dollars.

The Carb Box Step 2

This is what I mean by stranded wire. It has a number of strands of wire inside the rubber jacket. This works the best because the connector (a screw) holds onto it tightly.

The Carb Box Step 3

See the little screw? that screw jams into the center of the wire and positively connects with the little wire strands inside. The CDI box has the same kind of connector. Keep in mind this is ONLY for P-series bikes, I can't guarantee it is this way for anything else.

The Carb Box Step 4

Prepare the connectors with the rubber bits. put the larger bit on the end of the cap. This will seal out all the road dirt. Put the smaller one on the wire. Pull it back a bit so you can prep the spark plug wire. Make a straight cut across the wire end so that the wire will seat properly.

Cleaning the Air Filter Step 5

Now twist the prepared wire onto the screw until it feels tight. Give it a tug to make sure it wont pull off and slide the small boot down over the wire and onto the plug cap.

Inspecting the Fuel Filter Step 6

When you go to buy a plug cap, they may ask you what kind. You need a 90 degree NGK style cap. Typically the cap will plug onto the little threads under the connector. It's up to you what kind to buy, both work just as well, so get whatever's in stock. You may need a pair of pliers to get the silly connector off of the plug.

Time to buy a new filter when... Step 7

The final step is to get the old wire off your CDI box, a black box right near the rear shock. Pull the old one off the plug and unhook it from the shrouding. Next, pull back the boot and unscrew the wire. After preparing the new wire, slip the boot over the new wire and screw it into the CDI box. Hook the new wire back into the shroud and slip the cap onto the plug.

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All Material Copyright 2001-2024 by Richard Hoar. Use at your own risk.