Motorcycle Spark Plug Wires and Spark Plug Caps
The victim Suzuki GS500E
I need to replace the plug wires and spark plug caps.I know I need 7mm wires, but what resistance should the spark plug caps be?The bike uses a standard CDI ignition.Also,where do you purchase your plug wire and caps?
Caps, resstance . . . . .doesn't make a great deal differnece either.
If you are wanting to make up your own set, grab the old set, and find the local hotrod shop . . . .. they'll have all sorts of high-zoot wire and caps . . . . .
and not so high zoot, which will likely work just as well for your application.
If you're using resistors in the wires make certain you're not also using resistor plugs.
Resistance can be in plug wires (carbon thread core), plug caps, and/or
the spark plugs themselves.
The primary purpose is reduction of stray electromagnetic interference;
mostly with radio-type communications... But, those stray currents can
cause backlash problems for on-board systems; CDI units, computers and
With the simple Kettering system (battery/points/coil) no resistance is needed
except for radio interference. Not so with modern no points, high output systems.
Also, resistance in plug wires depends on length and resistance per foot; change length,
change wire type, change resistance.
So, changing the original amount of ignition system resistance can cause
Then taped the trigger down, and taped the light to the gas tank so I could see it flash
while riding the bike.... Of course you have to stop and change leads from one plug wire
to another. That pins down the grumpy cylinder. I also use a home-made spark tester
almost daily, which adjusts so I can see how strong (long) and regular each spark is.
Resistance-type plug wires can break internally if they are ancient and/or twisted all around.
Plug wire size matters little unless the coil output is super high, as used in some
very high performance hot rods/race bikes...
If you already know which cylinder misbehaves, you may be able to swap plug leads between
cylinders, or even coils/etc. If the problem moves along with the relocation..........
There are other causes of backfires. Too lean, which can be a due to vacuum leaks, partially
plugged jet or injector, valve out of adjustment or slightly burned, change of exhaust system and/or
intake systems, leaky head gasket. Vacuum leaks are common between carburetors and heads.
One recent Yamaha here popped and banged while running and when the air box was pulled back,
the carb fell off. The rubber manifolds had perished. Easy to check for vac leaks with a propane
torch (hey, not lit!)
Point is, since swapping parts is pricey, you really need to pin down what's what before maybe
buying more stuff you don't need...
^ This . . . . . . it may not be the ignition leads at all . . . . . .
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