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KZ400 fuse destroyer 11 May 2023 09:00 #884517

  • Feanor_twh
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The bike is burning the main fuse (20A).

It all started a month ago, suddenly the main fuse blew. I thought, these are fuses from almost 40 years ago, it could be normal. I replaced and all was well (except the idle is unstable, looks like is going to stop, but I didn't think that was related). Yesterday the main fuse blew again, I put in a spare and after about half a minute it blew again. I had to push the bike home.
Each time it burned while the engine was running and warm.

- I have checked the coil (green Dyna), correct resistances and the wires do not touch the mounting post
- I have ordered a resettable fuse so as not to accumulate a pile of blown fuses, it will arrive tomorrow
- I still have to check the voltage with the engine running to see if there are problems with the regulator (it's electronic, it seems unlikely). But I'll wait for the resettable fuse so I don't burn anything

Anything else I can try?
I also have this little gadget that suddenly appeared but I have no idea if it will work for this hehe
 
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard
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Last edit: by Feanor_twh.

KZ400 fuse destroyer 11 May 2023 10:26 #884519

  • Warren3200gt
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Sounds like you have a live wire shorting out someplace. Normal suspects are where the loom enters the the head light bucket. As you turn the handlebars the loom can rub on the headlight bucket hole and if it doesn't have the rubber grommet fitted can wear through the insulation and short out. 
Look for broken/worn insulation on any main live which is normally brown. 

Z1000J2 somewhat modified!

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KZ400 fuse destroyer 11 May 2023 11:50 #884523

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I would suggest you read through the "short circuit" fault diagnosis process in the attached guide. It will get you there without working through a bucket of fuses

www.kzrider.com/forum/forum-index/faq-wi...-fault-finding-guide

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KZ400 fuse destroyer 11 May 2023 12:41 #884526

  • Feanor_twh
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I would suggest you read through the "short circuit" fault diagnosis process in the attached guide. It will get you there without working through a bucket of fuses

www.kzrider.com/forum/forum-index/faq-wi...-fault-finding-guide
Thanks mate. We all want a quick and easy solution, but sometimes things go by calm down, study and understand.

I had a very difficult problem with the carburetion a long time ago and that was the only way to solve it.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400 fuse destroyer 11 May 2023 13:44 #884528

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Did you leave the stock wiring when you hooked up your reg/rec?
The original rec/rec battery charging wire isn't fused(white/red stripe) on a 400H.
If you tied into a line that is fused, you may overload the fuse when the reg/rec starts sending more current to charge the battery.

It could really be anything.
What did you add/modify electrically to the bike?
This could also be an item that only fails when hot.

You could also check the coil's primary resistance immediately after the fuse blows.
Just disconnect one of the coil's primary wires and measure resistance.
Compare that with the cold coil primary resistance reading.
 
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. Reason: clarity and grammar and ohhhh what about this....

KZ400 fuse destroyer 12 May 2023 19:32 #884572

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It could be a rubbed wire. Common places are under the tank, and wiring going into the headlight shell if the rubber grommet is all rotted and falling apart as most are by now. It could also be bad fuse clips causing the fuse to run red hot and melt. Usually you can see signs of plastic melted near the 20a fuse if this is the case, and rather than the fuse blowing, one end melts loose inside.
This was a huge problem and common. Touch the fuses and see if the 20a is hot. They run really warm even in normal operation, but it will be too hot to touch when the clips go bad. They can heat up from normal to red hot in a matter of seconds.
Really bad, and all the miles I rode at night I was just praying those clips would not leave me dead dark in the middle of the road.
321,000 miles on KZ's that I can remember. Not going to see any more.

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KZ400 fuse destroyer 12 May 2023 20:35 #884574

  • Kelly E
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I see in your signature that you replaced the handlebar controls. Once I replaced a right side control and a few months later I had the same problem. I had pinched a wire when I Installed the new control. An old guy told me a long time ago that the first place to look is the last places you worked.
The Rust Bros. Garage Collection
1974 Honda CB 550 K0
1975 Honda CB 400F Super Sport
1977 Kawasaki KZ 1000 LTD
1980 Suzuki GS 1100E
1981 Suzuki GS 1100E
1982 Honda CB 900F Super Sport
1983 Honda CB 1100F
1984 Honda Sabre 700
1984 Honda Interceptor 1000
1994 Kawasaki ZG 1000 Concours
And more
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KZ400 fuse destroyer 13 May 2023 06:16 #884580

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Did you leave the stock wiring when you hooked up your reg/rec?
The original rec/rec battery charging wire isn't fused(white/red stripe) on a 400H.
If you tied into a line that is fused, you may overload the fuse when the reg/rec starts sending more current to charge the battery.

It could really be anything.
What did you add/modify electrically to the bike?
This could also be an item that only fails when hot.

You could also check the coil's primary resistance immediately after the fuse blows.
Just disconnect one of the coil's primary wires and measure resistance.
Compare that with the cold coil primary resistance reading.
 
I renewed portions of the wiring but I kept the colors, the diameter of the cables and even the type of terminals.

Question: Can a coil that shorts when heated really blow the fuse? The issue of the blown fuses has happened at the same time as the loss of idling stability. That makes me think a lot about the coil.

Anyway, I haven't tested it yet. I've been busy moping and moping haha.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400 fuse destroyer 13 May 2023 06:20 #884581

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It could be a rubbed wire. Common places are under the tank, and wiring going into the headlight shell if the rubber grommet is all rotted and falling apart as most are by now. It could also be bad fuse clips causing the fuse to run red hot and melt. Usually you can see signs of plastic melted near the 20a fuse if this is the case, and rather than the fuse blowing, one end melts loose inside.
This was a huge problem and common. Touch the fuses and see if the 20a is hot. They run really warm even in normal operation, but it will be too hot to touch when the clips go bad. They can heat up from normal to red hot in a matter of seconds.
Really bad, and all the miles I rode at night I was just praying those clips would not leave me dead dark in the middle of the road.
When the fuse blew the bike stopped and I went immediately to replace it. It wasn't hot, maybe it got cold fast but the amazing thing is that the new fuse lasted barely 30 seconds. That makes me rule out a temperature problem in the fuse box.

I have to do tests, there is already a long list.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400 fuse destroyer 13 May 2023 06:22 #884582

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I see in your signature that you replaced the handlebar controls. Once I replaced a right side control and a few months later I had the same problem. I had pinched a wire when I Installed the new control. An old guy told me a long time ago that the first place to look is the last places you worked.
Thanks, I'll check this out too.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400 fuse destroyer 13 May 2023 07:12 #884584

  • F64
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Yeah, the coil could have internal wire insulation issues. As the coil gets hot the insulation breaks down which shorts internal windings.
If you have the old coil, you could swap it.
Or just check the resistance of the coil out of circuit when fuses start blowing.
 
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.

KZ400 fuse destroyer 14 May 2023 16:22 #884674

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Yeah, the coil could have internal wire insulation issues. As the coil gets hot the insulation breaks down which shorts internal windings.
If you have the old coil, you could swap it.
Or just check the resistance of the coil out of circuit when fuses start blowing.
 
I heated the coil with a heat gun (until it couldn't touch with my fingers) and this is what I got:

COLD: 14,50 kohm secondary, 3,2 ohm primary
HOT: 18,30 kohm secondary, 4,0 ohm primary

I think it's within reasonable limits.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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