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Hello everyone,

I have a pair of S150 Vespas, and one is giving me a bit of trouble. We were slated to go on a group ride yesterday morning, and one of the bikes died about a half mile from home... we had to push it back. After some digging here on Modern Vespa, I checked my spark plug wire, and it had worked itself loose. The problem is, I can't get it to stay seated. It immediately works itself off as soon as the bike starts moving. Do y'all have any suggestions/tips for me? My Dad says that I probably need to simply replace the wire, that they get hard with age on motorcycles, and won't stay clamped on to the spark plug. This particular Vespa is just over 2 years old, and has clocked about 8,000 miles. Thanks everyone in advance for your help! -Louie
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Are you referring to the wire coming out of the cap, or the cap coming off the plug? If the cap is not staying on the plug, either the cap or the plug may be damaged and one or both just need to be replaced. If the wire is not staying in the cap, are you just pressing the wire into the cap, or are you "screwing" the cap onto the wire? The cap has a threaded electrode in the center that actually screws into the center of the wire, in order to make solid contact with the copper core inside the wire. Try screwing the cap on as far onto the wire as you can get it to go, and it should be able to hold on pretty tight. If it still isn't staying on and your spark plug wire has enough slack in it, try cutting off the last 1/2" of the wire and screw the cap back onto the freshly cut end. Beware that some spark plug wires are very short and may no longer reach the plug if they've been shortened, so be sure to measure carefully before you cut. Hope this helps!
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bagel wrote:
Are you referring to the wire coming out of the cap, or the cap coming off the plug? If the cap is not staying on the plug, either the cap or the plug may be damaged and one or both just need to be replaced.
The cap is coming off the plug, and will not stay clamped onto it. I was figuring I'd probably have to replace either the cap, plug, or both... but hoped there was just some trick with these I wasn't aware of. Replacing the spark plug sure won't be fun, seeing how tight the area is! I might farm this one out.
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louielouie2000 wrote:
Replacing the spark plug sure won't be fun, seeing how tight the area is! I might farm this one out.
Though it sounds difficult, it is relatively easy to remove the lower shock bolt, unplug the sparkplug wire, and then jack up the body of the scooter to expose the plug. I use a scissor jack with a 2x4 underneath the scooter body. Make sure you raise it slowly, and don't catch any hoses/wires while doing so. Changing the plug then becomes an ease.
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The top of the plug has a small tip that screws on to the very top. If that has broken off or come loose in the head of the cap for the plug wire, this may be your problem.
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michael_h wrote:
louielouie2000 wrote:
Replacing the spark plug sure won't be fun, seeing how tight the area is! I might farm this one out.
Though it sounds difficult, it is relatively easy to remove the lower shock bolt, unplug the sparkplug wire, and then jack up the body of the scooter to expose the plug. I use a scissor jack with a 2x4 underneath the scooter body. Make sure you raise it slowly, and don't catch any hoses/wires while doing so. Changing the plug then becomes an ease.
What an insane design! (Reminds me of my '58 VW bug where one had to drop the engine to get to the forward-most plug). Am I right in assuming that spark plug maintenance only has to be done every hundred trillion miles or so?

My '62 Sportique was easy. Just remove the starboard nacelle and the plug sat there looking at you like a zit on a chin.

Why do vehicle designers come up with these crazy layouts? I realize that their first (and only) thought is make it quick and cheap to build, but really...
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Raputtak wrote:
michael_h wrote:
Though it sounds difficult, it is relatively easy to remove the lower shock bolt, unplug the sparkplug wire, and then jack up the body of the scooter to expose the plug. I use a scissor jack with a 2x4 underneath the scooter body. Make sure you raise it slowly, and don't catch any hoses/wires while doing so. Changing the plug then becomes an ease.
What an insane design! (Reminds me of my '58 VW bug where one had to drop the engine to get to the forward-most plug). Am I right in assuming that spark plug maintenance only has to be done every hundred trillion miles or so?
It is possible to remove the spark plug without jacking up the body. However, it is a tight fit if you have larger hands. In my case, it is actually quicker to jack up the body than it is to use the traditional method.
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XLR8 wrote:
The top of the plug has a small tip that screws on to the very top. If that has broken off or come loose in the head of the cap for the plug wire, this may be your problem.
I got out my flashlight and a small mirror and compared both bikes... that's exactly what happened. The "male" tip of the spark plug wire that connects with the "female" end of the spark plug has broken off... and appears to have lodged in the head of the spark plug. I went by and spoke with my local Vespa dealer, and he said this was a problem on the 250s, but this was the first 150 he'd heard of doing this. Fun times!
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You should contact Windbreaker on this forum. He came up with a good fix for this and posted a thread about it (but I can't find it right now).

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