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New guy with a 78 750e and questions

  • Thread starter Thread starter Kowalski
  • Start date Start date
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Kowalski

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Hello everybody I just bought a complete 78 750e with a title and a free spinning engine for a cool $360. I plan to "cafe" it, but keep it somewhat period correct. I managed to do this with my last build a 72 cb750 and ended up loving it. It's long gone though and this go around I'd love something a little better handling and a lower seat height. On paper this bike fits the bill perfectly. I plan on tearing it down to the bare frame and rebuilding it. Right now I have a few questions. The harness has hacked into and there's a random relay wired into the coil. I can't see this relay on any diagrams but is hate to bypass it if it's needed.
Next question is about the triple trees. I'd love to use a entire front end off a 84-ish GS1150. All balls has a conversion chart that tells me what bearings to use and I know the axles are the same diameter but I don't know if they're the same length. If they're not the same length is there another 37mm triple tree I can use that will allow these forks to work with my stock front wheel?

Well ill anyways here's the bike


heres that weird relay and some of the harness


 
Trace the wires coming from that relay and check the manual for the wiring diagram. Once it is traced, you should be able to tell if it is needed.


I like the starter "switch" ;)
 
That wiring looks scary. Especially things like that high side toggle witch with exposed screws.
 
The wiring is a mess. That relay is energized from the starter relay and controls power to the coils. I don't know what problem they were trying to solve by placing it there. The stator wiring is a mess too. I'm going to have a look on ebay and try to find a harness with a few less "repairs" on it.
Btw, does anyone know if I can run an 84 gs1150 front end, with my stock front wheel?
 
Kowalski said:
The wiring is a mess. That relay is energized from the starter relay and controls power to the coils. I don't know what problem they were trying to solve by placing it there. The stator wiring is a mess too. I'm going to have a look on ebay and try to find a harness with a few less "repairs" on it.
Btw, does anyone know if I can run an 84 gs1150 front end, with my stock front wheel?
Click to expand...

Depending upon whether that really is powering just the coils or ignitor as well it is called the "Coil relay Mod" or Ignition Relay Mod".
It is to over come voltage drops going back and forth through the harness and various connectors including the ignition switch. It is very common and highly recommended for the bigger bikes. Plan on leaving it in.

You should be able to that harness to functionality just make sure the fuse box is also clean and the R/R connections are clear.See GS Charging Health in my signature for a discussion. Also GS Sttor in my signature for a summary of R/Rs.
 
posplayr said:
Depending upon whether that really is powering just the coils or ignitor as well it is called the "Coil relay Mod" or Ignition Relay Mod".
Click to expand...
It's probably just the "Coil Relay Mod", as the '78 750 did not have an ignitor. :-k

Regardless, its purpose is the same. It's just a Band-Aid to cover up the real problem of dirty connections.

Since you will be cleaning up the harness, you might fix the root problem, but verify it when you are done.
Measure the voltage at the coils, compare that to the voltage at the battery. If more than a volt less, keep the relay.

.
 
I take it someone lost the key and didn't want to take it to a locksmith for a new one? The wiring is going to be so much easier once you get everything down to the frame. Get a good color wiring diagram (which is here, or I have one) then start tracing everything. See what will work now if you can, write it down, so you will have a good baseline. Bag and tag EVERYTHING. I spend well over $1400 on my 78 and I did things on the cheap. And it was a runner. Consider the SSPB from posplayr and read everything you can about the electrical system. All my electrics work (knock on wood) but it is just a matter of time for the stator. Good luck and take pictures.
 
The cb750 I built totaled around $1800 with a $600 buy in. I'm expecting this one to be similar but most likely a bit more. This harness doesn't scare me. I'm not trying to talk myself up but I'm a diesel mechanic at a Kenworth dealership and I deal with much larger more in depth wiring issues all the time. The charging system is another story, but I'll cross that bridge when I get to it. Thanks for all of the help and info!

Wedoo2, could I get a link to a color wiring diagram? I think I have a decent one but a few things aren't labeled on it.
 
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