Author Topic: 78 CB750K project, first motorcycle  (Read 7205 times)

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Offline thebluemax

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78 CB750K project, first motorcycle
« on: May 12, 2018, 10:04:55 PM »
Picked up a 78 CB750K about a month ago. Non running, all original, 4288 miles according to the odometer. No key. Had been sitting since 1984. Came with sales receipt, owners manual, title, insurance card from 1984, all in an envelope under the seat. Original Bridgestone tires (dry rotted but tubes hold air). Unfortunately the bike spent all it’s life in a saltwater climate which ate some of the metal, mostly just the chrome and wheel spokes.

Not sure where this project will go. The bike isn’t a restoration candidate since it’s to far gone. I’m thinking restomod.
Needs a boat load of work

Can I say that I love the recessed gas tank cap with the door and the smooth line?
« Last Edit: May 15, 2018, 08:25:38 AM by thebluemax »

Offline SOHC4 Cafe Racer Fan

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Re: 78 CB750K project, first motorcycle
« Reply #1 on: May 13, 2018, 09:16:15 PM »
Welcome and good luck. Feel free to ask any questions and post your progress.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #2 on: May 13, 2018, 09:42:30 PM »
How do I resize a picture to post on here?

Offline SOHC4 Cafe Racer Fan

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Re: 78 CB750K project, first motorcycle
« Reply #3 on: May 14, 2018, 06:37:40 AM »
After 10 posts, you can post photos on the forum.

Use either the attachment function or a hosting site like flcker
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #4 on: May 14, 2018, 09:14:42 PM »
Electrical  >:(

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #5 on: May 14, 2018, 09:15:28 PM »

Offline calj737

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Re: 78 CB750K project, first motorcycle
« Reply #6 on: May 15, 2018, 05:29:16 AM »
Electrical  >:(
? Problems? Wont start? Won't turn ON? No power?
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #7 on: May 15, 2018, 05:44:08 AM »
Following :)
Prokop
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Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #8 on: May 15, 2018, 05:53:47 AM »
All of the above.  >:(Replaced key, initially had blinkers and oil light but not taillight , headlight, or ignition. Checked fuses and found blown taillight fuse , replaced fuse . Fuse blew again and now I get nothing. I’ve got the battery cables clipped to my truck battery for testing since current motorcycle battery is dead. Haven’t had it tested yet to see if it has a dead cell or is still usable.

Pretty much learning everything as I go.

Offline calj737

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Re: 78 CB750K project, first motorcycle
« Reply #9 on: May 15, 2018, 06:05:52 AM »
To your knowledge, is the key switch original? Also, the RH switch pod is a common source of electrical issues. The wiring inside becomes corroded at the switch contacts.

Something to KNOW immediately on these bikes; solid BLACK is switched 12v NOT ground. Solid GREEN is GROUND. So if you have hooked anything up that was loose and have reversed the polarity of these wires, you'll be blowing fuses perpetually.

And make sure your car battery is hooked up correctly, obviously.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #10 on: May 15, 2018, 06:13:05 AM »
The original key was lost, so I had to buy a replacement emgo ignition switch.

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #11 on: May 15, 2018, 07:06:14 AM »
Dont rush it.  Try to turn it over using the kickstart.  If it turns over, drop the oil pan and see whats in there.  Just  make sure it is mechanically solid before you try to start it up. 
Prokop
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Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #12 on: May 15, 2018, 07:37:57 AM »
I know it turns freely with kick start and has 150psi compression across all four cylinders. But haven’t gotten any farther on that. Don’t have that much mechanical knowledge on motorcycles, I tore down,modified, and rebuilt an 80’s Chevy 4x4. Hope to get it all worked out.

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #13 on: May 15, 2018, 07:43:16 AM »
I know it turns freely with kick start and has 150psi compression across all four cylinders. But haven’t gotten any farther on that. Don’t have that much mechanical knowledge on motorcycles, I tore down,modified, and rebuilt an 80’s Chevy 4x4. Hope to get it all worked out.

Very good, you will be fine.    Checking the oil pan is easy and assurance that there is nothing it should not be there.  Some people do not bother with it but I do it on new to me bikes.

Electrical issue, it just takes a ohmmeter, voltmeter, schema, six pack and few hours of time. 

The wiring on 750 did not change much,  check this out:

http://oldmanhonda.com/MC/wiring750K1.html
Prokop
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Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline calj737

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Re: 78 CB750K project, first motorcycle
« Reply #14 on: May 15, 2018, 08:01:52 AM »
I think this is more accurate for a wiring diagram-
http://oldmanhonda.com/MC/WiringDiagrams/CB750(K8).jpg
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #15 on: May 15, 2018, 08:06:44 AM »
I think this is more accurate for a wiring diagram-
http://oldmanhonda.com/MC/WiringDiagrams/CB750(K8).jpg

no doubts  :)

posted that one for its educational qualities

Prokop
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Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #16 on: May 15, 2018, 10:00:04 AM »


Holy rust Batman

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #17 on: May 15, 2018, 10:53:01 AM »
Not bad at all  ;)
Prokop
_______________
Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #18 on: May 17, 2018, 11:29:48 AM »
Ohm’d out some of my wiring last night. Tail light and head light have continuity. Ignition does not. Also started making a parts list .
So far the bike needs:
Master cylinder rebuild at minimum/ replacement
Front caliper rebuild
Front brake line
Front brake pads
Possibly the front rotor

Probably chain and sprocket

Shocks and hardware

Petcock
Gas tank cleaning
Fuel lines
Carbs cleaned
Air filter
Carb linkage/cable


Tires front and rear
Rims and spikes are pretty rusty so probably need full replacement

Wiring issues resolved

Oil and filter

Kill switch/start switch replaced


Should I just tear down the bike and rebuild from the ground up?part it out , raise enough money to start  over with a running bike?


« Last Edit: May 17, 2018, 11:32:05 AM by thebluemax »

Offline 70CB750

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Re: 78 CB750K project, first motorcycle
« Reply #19 on: May 17, 2018, 12:25:16 PM »
Dorothy, my Blue bike, came to me in similar state.  I decided to get her on the road first, do upgrades and improvements and rebuild her later.  It took 5 years and 25 000 miles, now she is boxed up and waiting to be resurrected.  In the mean time I built Red, I just did not want to be without motorcycle anymore.

That said.  I would get her rebuild piece by piece starting with tires and brakes while keeping her on the road. Lot of people jump in head first, take the bike apart and loose steam in a year or two and end up selling it as a basket case.

My$0.02 only, of course
Prokop
_______________
Pure Gas - find ethanol free gas station near you

I love it when parts come together.

Dorothy - my CB750
CB750K3F - The Red
Sidecar


CB900C

2006 KLR650

Offline calj737

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Re: 78 CB750K project, first motorcycle
« Reply #20 on: May 17, 2018, 12:27:31 PM »
Short of replacing the tires and rims/spokes, that’s pretty close to a full 3,000 mile service. It’s only a few hundred bucks to do what you’ve described, and a couple of weekends.

If you’re replacing the rear shocks, spend the money and buy some Hagons or Ikons. Nils @Restorationcycle is a dealer and member here, gives outstanding service and pricing.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #21 on: May 17, 2018, 04:13:11 PM »
Would a 750F wiring harness fit a 750K ? I’m looking for a new harness

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #22 on: May 19, 2018, 05:39:35 PM »
Picked up Mac 4-1 exhaust last night from Craigslist. Started installing today before work. Will post pictures later.

Last night while on a plumbing service call started talking with the customer about bikes and turns out he used to have a SOHC 500 , followed by a DOHC 750 and numerous Norton’s,BSA, Triumph, and Harley’s. Long story short he told me he would help me with my project.

Offline calj737

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Re: 78 CB750K project, first motorcycle
« Reply #23 on: May 19, 2018, 06:19:31 PM »
Make sure to remove the existing copper crush gaskets from your exhaust ports and use new ones when you install the exhaust.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline thebluemax

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Re: 78 CB750K project, first motorcycle
« Reply #24 on: May 19, 2018, 07:39:56 PM »
Bought new copper gaskets and installed them. The collars that bolts to the head....are they supposed to be oriented one way or another?