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77 kz750 twin ignition

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18 Aug 2021 07:02 #854005 by Dan77kz750
77 kz750 twin ignition was created by Dan77kz750
I have a 1977 kz750. It's fairly new to me and has its share of issues from sitting too long. But everything has been going well till two nights ago. Was riding and bike totally shut off. Ended up pushing it 30 blocks to my closest friends house to store it till I could grab my truck, crappy night. 

after getting it home I started going through it and it appears the ignition switch is done after 45yrs. Jump around the switch and everything seems to work fine, bike kicks right over. 

New switch is on the way already. I've recently upgraded my headlight to an led unit that has a wattage of 45w/75w. I was not running the high beam at all.

Could this have caused the ignition switch failure or just bad timing due to age? Don't want to ruin another switch. 

Obviously can and will run a set of relays but not sure where to put them on the bike still and just trying to understand why something broke on my bike. Thanks for any help 

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18 Aug 2021 07:30 #854008 by Dan77kz750
Replied by Dan77kz750 on topic 77 kz750 twin ignition
After doing some quick math the stock light pulls 2.91A and 4.16A

My Led headlight pulls 3.75A and 6.25A

All of these currents should be capable of being run on 16-14ga wiring over this short of a distance. My relay setup will use 12ga just to be sure. 

I would think these levels of current wouldn't be responsible for the switch failure but i don't know. Hope it's just the switches age but don't want to be stranded again 

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18 Aug 2021 08:43 #854015 by DoctoRot
Replied by DoctoRot on topic 77 kz750 twin ignition
If the bike was stored outside for a long time i would not be surprised if all the switch gear had degraded some. The bike is 45 years old at this point, i doubt the headlight would have damaged it as long as you are still using the headlight fuse.

On a semi-related note - have you checked to see if you are getting full voltage to your coils? If your kill switch has degraded it likely is not passing full voltage to the coils. a popular mod on here is the "wired george coil mod" where in you use the kill switch to activate a relay that draws straight from the battery (use an inline fuse). it has made a noticable difference in startup on every bike i have done it to.

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18 Aug 2021 09:45 #854018 by Dan77kz750
Replied by Dan77kz750 on topic 77 kz750 twin ignition
I don't know that it was stored outside long term but the previous owner did it no favors. 

I also didn't think the headlight would have caused the issue but had to confirm that. I'm sure it's just age, not surprised at all. 

And thanks for the mod suggestion I will look it up, not sure how helpful it will be, my bike is kick only so I don't need a ton of power on startup.

And the previous owner disabled the kill switch for some reason, so I've just been turning it off with the ignition until I get around to replacing the controls with more modern replacements this winter. 

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18 Aug 2021 13:51 #854034 by Nerdy
Replied by Nerdy on topic 77 kz750 twin ignition
Here is the link:

wgcarbs.com/index.php/using-joomla/exten...-categories/89-COILS

This will put more power to the coils for easier starts and better ignition performance.

1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
2013 Yamaha FZ6R
The following user(s) said Thank You: SWest

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18 Aug 2021 16:12 #854037 by JR
Replied by JR on topic 77 kz750 twin ignition
Ignition switches do age and sometimes die from old age. Mine did  5 - 10 years ago.  I knew there was a voltage drop across it and then one evening  the bike just died at a traffic light. No lights, nothing. I got it started again by jiggling the key and with the proper use of swear words but that was it. Bought a replacement Emgo switch. The internal contacts wear and the solder degrades. Some switchs may be restorable but mine was not. I opened the old one up. It was pretty bad inside.

1980 kz750E1, Delkevic exhaust

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21 Aug 2021 07:53 #854141 by Dan77kz750
Replied by Dan77kz750 on topic 77 kz750 twin ignition
Ok so all I did was unplug the igntiojnswitches connector at the headlight bucket and plug it back in and now the switch works again. Faulty switch? Just dirty connections? 

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21 Aug 2021 08:45 #854145 by JR
Replied by JR on topic 77 kz750 twin ignition
Faulty switch or dirty connections? You will have to be the judge of that.

By all means clean the connections (Deoxit D5 is good) but while you are in there have a good look at the harness side of the connector block and at a wiring diagram and you can probably quickly figure out how to hotwire if the  problem happens again. Might save you pushing 30 blocks. 

in first post you mentioned you have a replacement switch on the way. If it were me I would install the replacement. You can probably use the new key in the gas cap and the old one for the seat lock. Not a major inconvenience in the grand scheme of things.

1980 kz750E1, Delkevic exhaust

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21 Aug 2021 08:54 #854146 by Dan77kz750
Replied by Dan77kz750 on topic 77 kz750 twin ignition
Definitely still going to replace it when my z1 shipment comes in. Just curious cause if it's connections I will save this factory switch as a back up. 

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26 Aug 2021 05:25 #854362 by Dan77kz750
Replied by Dan77kz750 on topic 77 kz750 twin ignition
UPDATE PROBLEM SOLVED 

Turns out the entire problem I was experiencing traced back to poor connections at the fuses themselves. Fuses were warm so I checked resistance and well that was the problem. Cut out the old fuse holders and wired up new blade fuse holders and the problem hasn't resurfaced. 
The following user(s) said Thank You: JR

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