Throttle Cable Shorted Out

[designbum]

Yesterday was beautiful so I decided to do a shake down run on my recently finished XS2. I decided to ride to Milwaukie, Oregon to visit my daughter who is recovering from surgery. It’s about a 25 mile round trip from my home and well I’ve got Triple A and my cell phone. The bike ran really great. Strong through the gears. I was pleased. After all it had been sitting in a garage for 6 years.
Ok. Visit complete, I headed back home hoping to avoid evening traffic. I ride back streets so all seemed good. I ran into a construction area routing traffic and became stuck in traffic as it was one lane. I just happened to look down at my left carburetor and saw smoke coming from the cable at the carb. The plastic jacket on the cable was starting to melt. I had my gloves on so I instantly pulled at the cable and the cable ferrule let go and ended the short. I’m thinking I’ll be walking now. I stripped the jacket from the cable and threw it to the side of the road. I just left the cable hanging. With nothing to loose, I was thinking I could have blown up if it had shorted against the tank, I started the bike again and it ran and nothing else was happening. Traffic started moving and unbelievably I had enough power from one cylinder to move down the road using only 1st and 2nd. I had nothing to lose so I proceeded to head home. Long story short, I made it and the clutch wasn’t even slipping.
I immediately pulled the tank thinking a big bare wire had rubbed against something but there was nothing but the spark plug wire with a big chunk of outer insulation missing, but no exposed wire. The wire also had some of the gray lining from the cable bound to it. I run a dual wire coil and am setup with the lost spark and points. I have checked everywhere and see no evidence of a short. I have my main power fused as well as my reg/alt. I’m lost. I plan on pulling the carbs and looking deeper for burnt wires. I have rewired some of the the bike and soldered most connectors that looked suspect along with shrink wrap. The wires are all taped into a loom and run along side of the backbone of the frame. I can’t think of what I could have done wrong but then again I’m the master of screwing things up. The bike has sat over night and does not show a power drain. I started it up briefly today and it sounded fine. Can the spark plug wire create a short even through primary insulation? I’m wondering if the spring over the throttle cable possibly was pinched against the plug wire when I installed the tank the last time. Meanwhile I’ll be ordering new cables as the right one shows signs of melting also. Tomorrow, off with the carbs to dig deeper. I did discover my right carb is grounded but the left is showing something like .04 volts. Weird. I suspect a grounded carb really doesn’t mean anything unless it hits a hot wire. Any you guys ever ground a throttle cable? Thoughts, comments, and criticism accepted.

 

[GLJ]

You have a frame to ground at the battery problem. Run a ground wire from the negative battery post to the frame. I will bet that solves your problem. The way your bike was built it had a ground cable from the battery to the rear of the engine case and then relied on the bolted connections of the engine to frame for the ground path for the frame.
Since you said you restored your bike you probably repainted the frame. Paint is a good insulator. When I resurrected my XS2 I had the frame powder coated. I didn't want to remove the paint everywhere the motor bolted to the frame. What I did was was run all the ground wire to a central point on the frame and then run another wire from there to the battery. It's also a good idea to run a ground wire from the handlebars to the frame as the handlebars are rubber mounted.

 

[Mailman]

My first thought when I read this is , usually when something weird is happening in the electrical system it’s usually due to a bad ground. On both of my bikes when I restored them , everywhere that there is a ground connection to the frame , I took a Dremel and shined It up to bare metal, battery, motor mounts, and ignition. The switch gear has to have good ground connections up in the headlight bucket, the handlebars are rubber mounted. If they don’t then they will try to ground through the switches or in some weird way through the harness.
In trying to figure out how your throttle cable became energized and you didn’t see any obvious shorts along the cable, I was wandering if maybe there could be a problem inside your switch gear/ throttle housing that’s shorting to your cable? Might be worth opening them up and looking for something obvious.

 

[Mailman]

Ha! Greg beat me to it!

 

[GLJ]

I was wandering if maybe there could be a problem inside your switch gear/ throttle housing that’s shorting to your cable? Might be worth opening them up and looking for something obvious.

Good thought. Since the handlebars are rubber mounted a short in a switch could be trying to go to ground through a throttle cable.

 

[designbum]

Hey, thanks guys. I have a lot of grounds to the frame but my main ground Is the engine. I’ll add beefy ground to the frame just to be sure. I’ll check my controls (they are new, 75B) style) and establish a ground to the bars also. The throttle is nylon type not metal so l can’t see why they would short there. As I said the plug wire melted against the throttle cable but that could certainly have been because the cable became so hot it melted into the plug wire. All of my controls are working normal I think. I’ll pull the control and have a look. Thanks for the input. I did a 100 mile ride around Mt Hood a couple years ago and one guy on an old Guzzi had his throttle cable fry due to chapping a hot wire. We got the cable freed and he also limped home with a completed ride. I always try and make sure everything is good under the tank but you never know where all those wires and cables end up. I did get a full voltage reading on the right carb that was still hooked up. Thanks again for something to go on.

 

[designbum]

Just did a voltage check on the throttle cable alone and got a 4v reading with the light switch on. 6v on bright. Also a 4v reading through the bars. Tested with ignition switch and kill switch on and only show voltage when I switch on the lights.

 

[JAX71224]

Some weird carbs needing voltage? WTF