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Hi guys. Leave it to me to have a strange issue...I have a 1980 200 Twinstar. It has been starting and running since I got her, but ran bad, would only give me about 40 mph. I decided this winter to put her on the operating table. The carb/fuel system was absolutely nasty and contaminated. Got all that corrected. Check...The bike didn’t have a horn installed. I have a 6V Honda horn, so I put it on there. Once connected, my electrical system went to hell in a hand basket. With the horn connected, when I turn the key on, I BARELY get a dim neutral indicator, and nothing else. No spark, no run, no horn, etc. disconnected the horn black wire, and lights, starter, etc work as they should, but now still no spark. I stripped the bike down, exposed the entire wiring harness, and checked that everything was connected where it should be per the wiring diagram, cleaned all the ground connections with a scotch-brite pad on a die grinder, Ohmed the grounds with a VOM, installed new plugs, cleaned the points, and using a small battery charger, my battery is holding 7.14 volts during all my checks. Before all this, it would start the instant the button was pushed, or with one kick. Main fuse is good to go, all wiring was checked visually from end to end, connectors checked for corrosion. I can’t figure out what I’m missing, and I can’t imagine that connecting a horn (without even pushing the button) would kill my coil. I felt confident that cleaning the fuel system, would give me good running bike to enjoy remembering my childhood memories, it’s deflating to say the least. I have an aircraft shop, and am no stranger to odd electrical gremlins, but this thing has me floored! Any help is greatly appreciated.
 

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Update: bike has been sitting for 6 days un-touched...checked it this morning before my post, and no spark. Went to the grocery store with my wife, came home....just for kicks, hit the start button: instant start and run... WHAT THE HECK?!?
 

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Can't speak for the bike you have, but many older Hondas suffer corrosion on the internal contacts of the ignition switch and often need to be taken apart and the contacts cleaned. Turning the key on and off many times has a tendency to clean up those connections briefly, so maybe that's what happened
 

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Sounds like you are on the right track. Honda horns are a little bit of a mystery to me, but the circuit is pretty simple. On Hondas the Green wires are ground and the black wires are switched (ignition on) power. The horn is connected to the black power wire and the circuit to ground is completed through the horn button. Part of the horn mystery is how they work, but I would guess there is a coil and some kind of a mechanical relay or points that will move the diaphragm and break the circuit. If could be possible the horn has an intermittent short that can cause a low voltage condition to exist when the key is on.
 

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Discussion Starter #5
I will have to check the horn out. The terminal end on the black wire looks like it’s been hot. I left it disconnected, and took the bike out. It’s very windy, rainy and cold here, but it gave me 69 mph. I went a couple miles. On the way back, it seemed to “give up” at 55, I pulled the choke up about 1/4 inch, and it cleared and ran right back up to 69-70. Guessing I’m a tiny bit lean? It isles awfully high, and the idle screw has no effect idling down, but it will idle it up more.
 

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I would suspect you are passing some crud through the carburetors. There should be a screen in the petcock bowl. You might try having a look at that. 69-70 is about it for one of these bikes. On the electrical side, there needs to be a good ground between the handlebars and frame of the bike. Honda took different approaches to this over the years. Most likely it is through the green wire in the harness. If the turn signals and headlight are working well then it is probably good.
If the bike is in perfect tune and you have a long enough straight away, a good racing tuck and you are not too big, you might see 80 out of it. But there is nothing like trying to explain yourself to the cop after he has followed you for two miles when you are in the tuck racing position. Don't ask me how I know...
 

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Discussion Starter #7
I’ll be pulling the carb again when it warms up. I have had to turn the mixture screw way too far out to keep it from bogging off idle. Electrically, the lights all work great. Something odd though, is while it was running, I hooked the horn wires back up. Electrical stayed working correctly, except the horn wouldn’t beep. I have the throttle a good high rpm wrap, and all of a sudden the horn began blowing!! Without me pushing the button! I disconnected the wires again.....looks like my handlebar horn switch is at least part of the issue. I’m appreciating the replies. Hopefully this all will help someone else down the road. I’m almost certain the carb on it is not an OEM carb, that may be some of the issue too.
 

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I wouldn't think the horn is the issue. They either work or don't. Test the horn off the bike. Small screw on the back adjusts the diaphragm to tight or to loose and no horn. I'd suspect the hand control. It's a bit tricky to work on but it can be serviced. Clean it up well, get all the grease out of it. Use dielectric grease to re lube it. I've found the horn button often needs to be shimmed a small amount to sit properly. (Caution, a lot of very small parts inside this switch!!)
 

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Discussion Starter #11
Thanks. I will be cleaning the tank too. Everything works correctly, even lock to lock. I do have a multimeter. I may just leave the horn out of the circuit and just yell “BEEP!” ?
 

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with a cornish accent?

so the problem occurs with the horn involved?

see wiring diagram for how that is wired, on black wire ( battery voltage after the ign switch is on ) and one an other color going to the horn push switch, then to earth?

They are strippable but yes, small parts in there, feeler gauges come in handy, especially to re assemble them.
 
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