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Kz750e No spark, trouble building the gm hei mod 27 Nov 2015 21:23 #700857

  • VegasRob
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I recently purchased my first bike. It's a half finished kz750 project that pulled me into a love affair with irrational decisions. I hate to beat a dead horse, as this topic seems to come up alot on the forums, but I haven't been able to get a spark out of this machine. I've read through several threads about trouble shooting the ignition system on these old bikes but had trouble finding something specific to the 81 kz750 four cylinder with points. I am attempting to build and install the gm hei mod because it seems straight forward and eliminates the need for the condensers and replaces the ignition box in one step. I found a link for the circuit diagram and built it but I must be missing something cause still no spark. One of my coils ohms out as faulty on the secondary but that doesn't account for no spark on the other two cylinders. I'm hoping one of you fine people on this forum can help me out.

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Kz750e No spark, trouble building the gm hei mod 27 Nov 2015 21:39 #700859

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VegasRob wrote: I recently purchased my first bike. It's a half finished kz750 project that pulled me into a love affair with irrational decisions. I hate to beat a dead horse, as this topic seems to come up alot on the forums, but I haven't been able to get a spark out of this machine. I've read through several threads about trouble shooting the ignition system on these old bikes but had trouble finding something specific to the 81 kz750 four cylinder with points. I am attempting to build and install the gm hei mod because it seems straight forward

As a suggestion: if you can't troubleshoot a points/coil system, I would not complicate things further by trying to redesign the system.

Points/coil is the simplest circuit in existence. You have a coil (which is a transformer) with a primary (low voltage) side that gets +12V on one terminal and the points line on the other. The latter is usually a blue wire that runs to the points. Turn on the key: do you read about 12V on the "hot"terminal on the coil (look for a yellow, red or yellow/red wire). If so, good. Turn key off.

Find the points wire on the coil and loosen the nut to free the wire. Hook the ohm meter to ground on one lead and to the points wire on the other. Use the kick starter to rotate the engine and watch the points open and close. Ohm meter should read zero Ohms when points close, infinite (open circuit) when they open.

If those two things check out, your coil should fire a spark unless the coil is bad.
1979 KZ-750 Twin
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Kz750e No spark, trouble building the gm hei mod 27 Nov 2015 22:05 #700860

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I'm not sure if the wire harness on this bike is still intact stock. From the points there are 3 wires one from each point (one black, one green) with a matching short run down to each condenser, and blue wire with red stripe that runs to the back of the plate. Up at the coils on the primary side there is a red wire with battery voltage running to each as well as a black wire on the other terminal of one and a green wire on the other terminal of the other. When the key is on and the kill switch is on then there is 12 volts at all 4 terminals on the primary side of the coils.

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Kz750e No spark, trouble building the gm hei mod 27 Nov 2015 22:09 #700861

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I'll be a little more thorough checking the circuit.

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 00:03 #700862

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The 750-4 has electronic ignition, not points; the pulsing coil has 2 pickup coils.
Right side 1-4 ignition coil = black + red
Left side 2-3 ignition coil = green + red

I installed the green Dyna 3.0 ohm coils & spark plug wire set from Z1Enterprises.com. The grey 2.2 ohm are a better match for the stock electronic ignition, but I got the green for in case I switched to the Dyna S ign.

You may need to redo the spark plug wire connections. unscrew the ribbed compression boots from the ign coils. If there's the white crusty oxidation, nip off the ends of the wires a tad. Or install new 7mm copper core spark plug wires.

Be sure to clean & lubricate the timing advancer. Separate the rotor from the body & fill the groove with grease. I use high temp wheel bearing grease.

Here's a site w a pdf manual & wiring diagrams. mbsween. bike-night. KZ750L3 . Scroll down & click "The Bible" link.
Note: some of the wiring diagrams are mislabeled in the links: the 1981 Ltd is an H2, the 82 is an H3, & the 83 is an H4.

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 03:22 #700873

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+1
I'd like to see a pic of the 'points'.


.
2002 ZRX1200R
81 GPz1100
79 KZ1000st daily ride
79 KZ1000mk2 prodject
78 KZ650sr
78 KZ650b
81 KZ750e
80 KZ750ltd
77 KZ400/440 cafe project
76 KZ400/440 Fuel Injected

www.dotheton.com/forum/index.php?topic=39120.0


.

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 05:11 #700893

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Right. If the bike is a 1981 KZ750 and if it has points ignition one of the following 2 things were done:

1. Someone has removed the original engine and installed an older engine - most likely a KZ650 engine.

2. Someone has removed he original ignition system and replaced it with a points system - probably from a KZ650.

Pictures would help us solve the mystery. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 05:56 #700914

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Hopefully the picture works, I'm new and still figuring out how the site works.

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 06:06 #700916

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No pic?
Attachments:

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 06:15 #700918

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The condensers need to be hooked up. Clean the points with a nail file and folded match book cover. If there is sparking at the points the condensers are bad.
Steve

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 06:51 #700925

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The points are clean, spark plug wires and boots clean. No sparking anywhere to be seen. Is there a way to check the condensers with my meter before reconnecting them? I'm thinking I have multiple faulty components on this frankinstein bike. I was able to get a good resistance check done up at the primary side of the ignition coils, the secondary side I'm not sure if I check between the two leads or from each lead to ground.

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Kz750e No spark, trouble building the gm hei mod 28 Nov 2015 07:01 #700927

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The points can look clean, just a little oil or grit will ruin a day.
Steve

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