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Spark Plug Gap 03 Jul 2020 20:04 #829725

  • luisazmz
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Hi all. I’ve been rebuilding a KZ750 I purchased a couple of years ago, so far so good. Only thing I’ve yet to figure out is the following. If I gap the spark plugs to what the manual recommends .7mm, they don’t produce spark. I can tell thanks to the timing gun. If I set the gap to something like .05mm (excuse my metric) a gap ridiculously small as if it were a racing bike, the engine starts right up. What could be causing the spark to be so weak when gapped to the appropriate spacing?
For reference, I’m running new coils with the appropriate resistance on both the primary and secondary winding. Running a new fully charged battery and the dynamo/regulator are working flawlessly.
Thank you in advance.

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Spark Plug Gap 04 Jul 2020 09:14 #829753

  • Warren3200gt
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Points or electronic ignition?

Z1000J2 somewhat modified!

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Spark Plug Gap 04 Jul 2020 10:38 #829761

  • luisazmz
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It's a KZ750B Twin with Points. One thing caught my attention is that when the ignition is set to ON the resistance from the battery to the engine 0Ω when the point system is open. When the points are touching it jumps to about 17Ω. Should this be happening?

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Spark Plug Gap 04 Jul 2020 12:51 #829775

  • gd4now
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You need very close to full battery voltage at the coils to get a good fat spark.
1977 KZ650 B1
Pods and Denco header


This is my Z

OLD KAW OWNERS SMILE ALOT

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Spark Plug Gap 04 Jul 2020 20:00 #829807

  • F64
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Luis,
Let's check some voltages.

Bike ignition on but engine not running.
Meter set to DC V

Black meter probe on negative battery post
Red meter probe on positive battery post.
Note voltage

Rotate the engine with a wrench till points are closed and touching.

Black probe on negative battery post.
Red probe on coil 12v+ wire
Note voltage

Move red probe to the negative coil wire.
Note voltage
Rotate engine till points are fully open
Probes in the same place
Note voltage
Turn off bike---coils may overheat if left on for too long.
81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY

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Last edit: by F64.

Spark Plug Gap 04 Jul 2020 20:04 #829808

  • F64
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I double posted...too much coffee
81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY

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Last edit: by F64.

Spark Plug Gap 05 Jul 2020 13:42 #829870

  • luisazmz
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Let's check some voltages.
Meter set to DC V
Black meter probe on negative battery post
Red meter probe on positive battery post.
Note voltage - 12.6V

Rotate the engine with a wrench till points are closed and touching.
Bike ignition on but engine not running.
Black probe on negative battery post.
Red probe on coil 12v+ wire
Note voltage - 11.5V
(interesting thing happens here: the wire that goes from the ignition switch reads 12.5V, but when I connect it to the coil it jumps to 11.5V)

Move red probe to the negative coil wire.
Note voltage - 12.5V

Rotate engine till points are fully open
Probes in the same place
Note voltage
coil 12v+ wire: 12.6V
negative coil wire: 12.6V

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Spark Plug Gap 05 Jul 2020 13:51 #829874

  • F64
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really quickly, i notice your points aren't grounding when they are closed.
You also have a bad voltage drop on your coil posotive line.
I'll write some more when I get inside in a couple of hours.
We'll also test more to get rid of that voltage drop.
81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY

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Spark Plug Gap 05 Jul 2020 15:17 #829881

  • F64
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Ok
meter on DC V
Bike ignition on but engine not running
Points closed

Red meter probe on negative battery post
Black meter probe on coil negative wire(blue wire).
Note voltage
move black meter probe to the points screw with pink arrow.
Note voltage

The reason your voltage drops when you connect the wire at the coil is the circuit is now under load.
Current is now flowing.
When you do voltage drop testing the circuit has to be fully connected and on.
It's pretty easy when you understand the technique.


photo by charka129
81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY
Attachments:

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Last edit: by F64.

Spark Plug Gap 05 Jul 2020 15:33 #829883

  • luisazmz
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I'm getting a number very close to 0V. If I open the points it jumps to the battery voltage about 12.6V.
I’m doing all these tests with the engine STOP switch set to RUN.

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Spark Plug Gap 05 Jul 2020 16:00 #829887

  • F64
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what was the voltage at the negative terminal of the coil?
I need 2 voltages.
The one at the coil and the one at the points.
Label which one is which.
81-KZ440-D2.
Louis Dudzik's GM HEI ignitor conversion installed 2015 s3.amazonaws.com/gpzweb/Ignition/GPZgmHEImod.html
Motogadget m-unit blue installed 2017.
LIC, NY

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Last edit: by F64.

Spark Plug Gap 05 Jul 2020 16:48 #829891

  • luisazmz
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Battery voltage 12.9V

Points Touching
Coil Negative Terminal : 0V
Coil 12V+ Terminal: 11.82V
Points: 0V

Points Open
Coil Negative Terminal : 12.88V
Coil 12V+ Terminal: 12.88V
Points: 12.88V

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