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"Beautiful BC" ~ A build

Lone Vagabond

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Hey Guys,

Picked up a '76 CB750 few weeks back. Got it for $100. It happens to be in the amazing basket case state that I seem to attract.

Pros-
  • free motor
  • good battery
  • good wheels and tires


Cons
  • Bad title
  • electrical fire
  • no carbs
  • cables needed
  • sticky clutch
  • single brake, needs rebuild too

The first hurdle I need to clear is the wiring. Is there perhaps someplace I can find a listing of the wiring gages for a custom harness? I've done some searching but can't seem to find anything. I have the Clymer book but can't find any specs on wiring other than diagrams. Do you think I could adopt a wiring list and diagram from here? http://www.xs400.com/forum/showthread.php?t=5934

Second is a clutch that doesn't seem to fully disengage. I can hold the bike in place with the clutch pulled in while kicking it over but it wants to move. If I want to simply pull the clutch in and roll the bike there is enough clutch catching to drag the rear wheel. I've played with the cable and the clutch adjustment screw and at a certain point the clutch pops. I'll have to upload a video for you all to watch in the next few days.

Ordered the Clymer book, cables, carbs, and coils. I did the noob thing and didn't sit down with the bike before ordering things and I already had coils. :doh:

This bike is now basket case number two for me. I've got a XS400 with a good thread over at XS400.com

here's the linky http://www.xs400.com/forum/showthread.php?t=8885

so there you can learn more about me but on to the pictures now.

I'll have a few more photos in the next day or two. But just so you all know I've got just a few weeks left of school so I'll be scarce till mid-december.
 

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I would get it running first then try the clutch. If it has been sitting for a while the clutch will drag until you get some oil in the plates. There are some electrical diagrams on this site. Look in the gallery, its on the last page I believe. I just use 12 ga on all the wiring in my harnesses.
 
So I went and worked on the bike last night as a break from homework. Came to three realizations

1. With the electrical fire, the oil supply hoses were burnt through and the motor is essentially dry.
2. As much as I'd like to use a stock carb setup, the '76 is a rare bird. I'm going to save up and go to the Bike Exchange twin carb setup.
3. All we need in the garage now is a Suzuki and we will have all of the major metric bike makers. Along with a BMW thrown in for good measure. haha

So it looks like i'll be in a holding pattern for the time being till i'm done with school and have a real job.
 
There isn't anything special about the stock carbs on the 76 it used the old round top carb. For sale on ebay all over the place. But the cycle X setup will run better.
 
Hey nice to see you over here! I don't think you ever really said what your plans were for this bike.. just get it up and running and titled?

For the wiring, do you have a harness at all? You could check what the stock wiring sizes are for each component and go from there. Most wiring on every old bike I've looked at is 18 gauge. Generally the wiring is thicker for circuits with larger fuses. You might want to use larger wire for the regulator, headlight, ignition switch, and a couple of other things, but 18 gauge would probably work for the majority of it. If the circuits are long you might run in to some voltage drop with the smaller wires. You have to consider the load on each circuit and length of each circuit to determine the wire and fuse sizes (length isn't usually a problem on motorcycles). Some switches aren't meant to run a ton of amps, so if you up the load on the circuit (say higher wattage headlight), you could use relays so that the smaller circuit that the switches are connected to can control the circuit with the larger load.

Running bigger wire won't really hurt anything as long as the load hasn't changed, so some people just use 16 gauge for most things and 14 for the bigger stuff as an additional safety factor. It will make your harness slightly larger though.

If you want to get real technical, you could measure the ohms or watts of each component in a circuit and figure out the total amps to determine what size wires you need. Power (watts) = Volts X Amps, so Watts/Volts = Amps. So if you have a 100 watt load at 12 volts, you have 8.33 amps. You can find charts online that show the wire gauge to use for the amps and circuit length. Here's one that would probably work: http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm. Notice that 18 ga is recommended for everything except for high amps or long runs.
 
"Hey how do I get multiple quotes in a message? I'm struggling to figure that out... and i'm the kid. I should know this."

Read the FAQ. stupid kid.... haha

Tired it still don't get it. Help?
 
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For sale on ebay all over the place. But the cycle X setup will run better.

digger, I bought some off of fleabay. began the rebuild by tearing them down all the way. Pictures soon with questions.


just get it up and running and titled?

For the wiring, do you have a harness at all? You could check what the stock wiring sizes are for each component and go from there. Most wiring on every old bike I've looked at is 18 gauge. Generally the wiring is thicker for circuits with larger fuses. You might want to use larger wire for the regulator, headlight, ignition switch, and a couple of other things, but 18 gauge would probably work for the majority of it. If the circuits are long you might run in to some voltage drop with the smaller wires. You have to consider the load on each circuit and length of each circuit to determine the wire and fuse sizes (length isn't usually a problem on motorcycles). Some switches aren't meant to run a ton of amps, so if you up the load on the circuit (say higher wattage headlight), you could use relays so that the smaller circuit that the switches are connected to can control the circuit with the larger load.

Running bigger wire won't really hurt anything as long as the load hasn't changed, so some people just use 16 gauge for most things and 14 for the bigger stuff as an additional safety factor. It will make your harness slightly larger though.

If you want to get real technical, you could measure the ohms or watts of each component in a circuit and figure out the total amps to determine what size wires you need. Power (watts) = Volts X Amps, so Watts/Volts = Amps. So if you have a 100 watt load at 12 volts, you have 8.33 amps. You can find charts online that show the wire gauge to use for the amps and circuit length. Here's one that would probably work: http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm. Notice that 18 ga is recommended for everything except for high amps or long runs.

The stock harness was all burnt up. I'll just be using 12, 14, and 18 gage wire. I will get technical once I'm done with school... seems to be an echo in here...

I'll get it running first then I'll be taking the custom frame I'm making and use that for this project. The XS is going to be more about rebuilding than customizing.

Tired it still don't get it. Help?

Well I figured it out....
 
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