Does anyone know what the purpose of a sparkplug boot is? I am trying to get an old moped to run and I was getting no spark with the plug connect to the boot, but then I cut the boot off and just connected the bare wire to the plug and I get a spark(unfortunatly it still isn't running). The boot says 5Kohm on it, what is the point of having so much resistance before the plug? Should it run without the boot, just hardwired like I have it?
Spark Plug Boot
- Thread starter bigal40
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hanoverphist
Diamond Member
- Dec 7, 2006
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doesnt the boot keep it protected from spark jump? if the clip had been pulled back into the boot a bit and wasnt connecting to the plug, im sure it wouldnt spark at all. i had the problem on an old chevy truck i used to own. also, check with the moped manuf. to see what the resistance should be on those cables, then check the cable itself with a meter. could have a bad one.
brblx
Diamond Member
- Mar 23, 2009
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the boot just insulates the plug and wire terminal.
the resistance is in the wire itself, it's there because ignition systems are low amperage and high voltage. if you pumped thousands of volts through a wire with little resistance, your plugs would be using a shitton of current.
the resistance is in the wire itself, it's there because ignition systems are low amperage and high voltage. if you pumped thousands of volts through a wire with little resistance, your plugs would be using a shitton of current.
boomerang
Lifer
- Jun 19, 2000
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I think there may be a terminology problem here. By boot, are you referring to a hard plastic boot versus a soft rubber like boot?
Some older motorcycles had a hard boot that provided resistance to the circuit. It was to keep from messing up the radio reception on cars near the bike. This was in lieu of using resistor spark plugs. This is a moped so this may be the situation.
BTW, usually you just unscrew the boot from the wire. There is a threaded stub in there and the boot screws onto the wire.
Some older motorcycles had a hard boot that provided resistance to the circuit. It was to keep from messing up the radio reception on cars near the bike. This was in lieu of using resistor spark plugs. This is a moped so this may be the situation.
BTW, usually you just unscrew the boot from the wire. There is a threaded stub in there and the boot screws onto the wire.
SpatiallyAware
Lifer
- Sep 7, 2009
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Yes, I think this is the what was going on with my moped(it is a 1977). The "boot" was a hard L shaped piece of something like plastic or ceramic. I unscrewed it from the end of the spark plug wire and I got no connectivity between the two ends, so I assumed it was bad. Out of curiosity I cut it into slices and It was like plastic w/ like a white material inside - I guess this was the resistor.
So the question is - will the bike run without the resistance since it was there to help w/ radio interference?
If you start seeing puzzled looks on driver's faces when you get close to them on the Moped, you'll know you're messing up their radio reception.
Yeah, If I can ever get the thing to run.
Anyone Know anything about mopeds?
I am getting a nice spark, gettting compression of 110psi(this is a bit low, but shouldn't be low enough to keep it from starting), and I am getting fuel into the cylinder(the plug is wet/I can see it spraying out when I turn it over w/ the spark plug out). It was in really bad shape , but I rebuilt the carb and rebuilt the engine(except for the crankcase just b/c I don't think anything is wrong w/ it) but I can't get it to start. It doesn't even seem like it wants to start - I just get an occasional pop when turning it over.
http://www.youtube.com/watch?v=uZVypo0Trik
Pull the plug and clean all the fuel off of it. Turn the engine over to expel any raw gas. Squirt a little alcohol into the chamber thru the plug hole. Install the cleaned plug, hook the ignition wire up and turn her over.
That should work. Isopropyl alcohol is what I generally use in situations like yours.
boomerang
Lifer
- Jun 19, 2000
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Spark, compression and fuel. The basics - and you've got them.
When it still won't start, then you've got to look at things like, is the spark occurring at the right time? Too much fuel? If the spark is created by a magnet on the flywheel rotating past the coil, make sure the flywheel key has not sheared. You'll still get a spark, but at the wrong time.
Is this a two-stroke? A vacuum leak in the crankcase area can be very difficult to diagnose. The crank seals have to hold both pressure and vacuum.
When it still won't start, then you've got to look at things like, is the spark occurring at the right time? Too much fuel? If the spark is created by a magnet on the flywheel rotating past the coil, make sure the flywheel key has not sheared. You'll still get a spark, but at the wrong time.
Is this a two-stroke? A vacuum leak in the crankcase area can be very difficult to diagnose. The crank seals have to hold both pressure and vacuum.
Yes, it is a two stroke. It has points that open up to create spark and I have checked and they are openning up at top dead center. What do you mean by see if the flywheel is "sheared" ?
The only other thing is a leak in the crankcase like you said. That is the only part I have opened up and looked at. I thought it might be OK since it is getting fuel into the cylinder.
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