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Author Topic: "Poor Kid" 1981 CB750K - first build  (Read 26803 times)

Offline kraptastic k

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"Poor Kid" 1981 CB750K - first build
« on: May 01, 2013, 15:38:33 »
Hello all.

I bought an 81 CB750 from a guy in Dallas, TX as my first bike. This occurred in 2011, I believe December, when I was waiting tables at a sushi restaurant and living in a different county. Cost me $600 initially. Here are a few flattering shots from PO (we're now friends after the trade) and some less flattering ones as I rip it apart.

Note: This bike was in rideable, fixable shape- but for some reason, I couldn't leave well enough alone. Maybe perfectionism?

Offline kraptastic k

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"Poor Kid" 1981 CB750K - first build
« Reply #1 on: May 01, 2013, 15:53:26 »
I started checking things out. The exhaust was rusty, but possibly servicable. The seat, which had been swapped from a smaller Honda bike of a different year, looked oddly perfect. I loved the classic lines of the bike.
 
The bike had only two PO's, but it had taken an apparent beating... I started developing a plan to fully remake it in a more desirable image.
As I had yet to really get into the scene and become self-aware, I was setting myself up for cafe 'ricer' status... worried about cheap filters and stupid bars and shit. Just copying what I saw in photos on google for "cafe motorcycle..." ugh!

Unfortunately, I was too proud to ride around on a semi-stock rust rocket. I pulled some other things, such as broken bar controls, fried ignition units, and a loosely dangling front brake master cylinder that read "Kawasaki."
Also, the choke cable was hanging out the left side of the carbs, duct-taped around a hose clamp as a makeshift handle. And it wouldn't cold start. And the tank had a huge fuckin' hole in it. As I worked through the initial phases of this plan, I saw more and more that I could not bear to leave alone.

Talk about getting in too deep... I had never even ridden a road bike before! I didn't know what a frickin' carburetor was when I purchased this bike. I wasn't certain of doing any of the "fixing" just yet. But I knew I could do the research and figure it out, because I've seen dumber people do cooler shit. So, over the course of about a year, I began accumulating parts. A ton of them, some OE replacements and some universal. I was applying more of the "bought" in "built not bought," and it would come to bite me right in the ass. During this phase, I did pick up my very rudimentary tools, which I'm still adding to. Didn't have much of a dad around for this shit.

I probably have spent about $2500 on the bike to this very day, when tools are considered as well. It still hasn't run.
« Last Edit: May 01, 2013, 18:39:24 by kraptastic k »

Offline kraptastic k

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"Poor Kid" 1981 CB750K - first build
« Reply #2 on: May 01, 2013, 16:06:59 »
So, I moved from apartment, to house, to yet another house with this bike, and all the boxes of parts I had accumulated. What an idiot I must have looked! But at this third dwelling I had made a change- a damn garage. Getting a garage has helped, but also job changes have permitted better income. Buying tools was no longer an object, and I committed to stop making excuses.

I took the front forks off to be rebuilt. I entrusted the job to a local shop. The place was sketchy and I'll never go there again- dude kept my forks for 6 months, giving me excuses about not being able to source some of the rings inside them. I found the ring, took my forks and my damn money home and did it like a big boy.

It wasn't a common job and I'll happily offer my advice to future DOHC builders on that one. I also had new tires mounted and balanced. I rebuilt the steering head and placed new bearings in it and in both wheels. Nice and greasy.

Knowing that most or all of the charging system was fried and mangled, I ripped every component out. Roughly $600 went to replacing the system. I was stuck on that bastard bolt as we began to call it- the alternator rotor bolt. I began work on it after the engine was out of the frame, which is apparently the worst time to jack with it. What a triumphant day when it came off! Unfortunately, a large chip in the case occurred before we got it off.

What a traumatic event... I was super pissed. A few days calmed me down and I got the epoxy out. Good thing this part of the case doesn't hold oil :( but it's a nice snug fit now.

Offline kraptastic k

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"Poor Kid" 1981 CB750K - first build
« Reply #3 on: May 01, 2013, 16:20:25 »
Ooof... just looked at the above pics. Need to get a real camera instead of a phone.

Anyway, so as space and resources were available, I began to move forward slightly. This was around October 2012 when momentum picked up slightly. I had pulled the engine out of the frame and discovered the suspension was totally dead in the back- the struts were as deflated as a 70 year old Kardashian ass.

I had an explosive moment when I went through the carbs and found that I could not confidently continue with them. The idea of being bound to that tacky ass airbox for the remainder of the bike's life was too low a ceiling. I gave the carbs and some rebuild kits to the PO of the bike for his CM400. Then, I bought some Mikuni BST36SS carbs, the ones from the GSXR-750s. As if I wasn't already lost in unfamiliar territory...

I painted up some engine cases after inspecting under the valve covers for rust. Oil was coating every surface and the gasket was in good shape. No reason it shouldn't work the same as it did when I took it out. Thank god I know how to operate a can of paint, I thought, then the shit chipped. And then I remembered it's 4 bucks a can, oh well! Only pissed me off because I did a 4 day process of multiple clear and color coats.

Further inspection under the front sprocket cover showed a ton of dirt/oil buildup and a severed wire. I forgot what it does, but I did a solid job soldering that punk back together. No room for error. I cleaned the crap out of that area to try and locate a possible oil leak, but no dice- the hull is intact cap'n. Unfortunately, the pulse generator cover appears to have been epoxied. It's not well done (by my standards, which are very f**kin high) and I'll have to redo it better.

Offline kraptastic k

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"Poor Kid" 1981 CB750K - first build
« Reply #4 on: May 01, 2013, 16:46:45 »
Thanks to Rich Ard for the ignition units above. You rock, Rich.

I cleaned the frame up slightly and covered some rust spots with (you guessed it) flat black. New suspension went on and I got wheels back from mount/balance. There's the stance... a sign of age I'm certain. Turning a cruiser into a streetfighter. But I ordered that suspension specifically for two up. And the seat looks like a brat seat. Hmm. Two- up Bratfighter? I don't know.

The carb swap is nearly complete. Yellow 1/4" fuel line for the vents and 5/16" fuel line.  I think I about nailed the boots but the hose clamps are far too long. K&N filters and Dynojet 136 mains are in place with all the Dynojet stage 3 shit installed. I hope the tuning is easy...

I put the exhaust on as well. Why not, right? Looks clean! I put the busted tank on for a mock yet again. Keeping me motivated. Unfortunately, I now wait on properly sized cables before I can install the air filters. That's what I get for ordering universal.

A new tank came in the mail a while back, I had previously treated it with The Works, but about a month with gas and Sta-Bil in it and I think it may need another rinse with acid. I know I'm not gonna be able to mount the tank and seat like this until I see a welder. I know a guy of good repute who I plan to have make me a whole subframe/rear tail light.

Unfortunately, I do not yet possess that level of expertise, garage builder elitists >:)

I am considering multiple options for tank styling. I am heavily influenced by MotoHangar's recent CB750 and I would like to try a brushed metal finish with clear coat. Does anybody have input on the process? I can furnish sample pics.
« Last Edit: Jun 01, 2013, 01:09:51 by kraptastic k »

Offline kraptastic k

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Re: "Poor Kid" 1981 CB750K - first build
« Reply #5 on: May 01, 2013, 17:07:32 »
To continue my meandering discourse from above:
I still would like to build this bike completely, all the way down to custom engine internals and tuning- however, as I am building skills, I want to get this bike back to running, legal status before all else. Understand my goal, gentlemen! Then hopefully I can build better with riding experience at hand.

As the Poor Kid currently stands, it is almost 100% road ready, with a few small caveats. I want it to remain slightly unfinished in case I drop the fegger on my first day. I hope you understand, crashing a perfectly polished bike would crush my heart. That's not to say I won't spraypaint or grind something just a bit for learning's sake. All things can be recreated with the right tools and experience. I think that's the lesson I've picked up here.

This week's Problem list:

I cannot source the front brake piston, as multiple orders and searches have brought me pain and a ton of returned shipping fees. When this is done, I can finally place fluid in the brake system.

I am working to finish the wiring, having repinned and soldered a good deal of the bar controls to obtain a clean(er) look. But as has happened before: I am confused by universal parts. This time, I am trying to wire the universal killswitch, which does not have a pinned connector. Also, the OE replacement reg/rec has one fewer wire. The present wires are pinned in a different configuration. This doesn't match the diagrams I have, building both headache and frustration faster than motorcycle. I suppose I will figure it out in the next days.

Throttle and speedo cables: too short/too long. Universal throttle tube wasn't compatible, OE cables were too long for clip on bars, etc. The usual. Handling it through Swifty's Motorcycle on Camp Bowie... What a great shop. Terrific service and absolutely competitive pricing. Support the locals! After this I can install air filters.

Everything else is totally finished. I'm still kind of in disbelief that I did this much, but I owe a great deal to this website and my friends. My standards are high, but I really need to see some critical commentary from other builders- I'm isolated from this community mostly by location.

Feel free to ask for other pictures if you can help with the above... otherwise, check back after I get paid hahah!

Thanks,

krap

Offline Rich Ard

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Re: "Poor Kid" 1981 CB750K - first build
« Reply #6 on: May 01, 2013, 17:26:24 »
Good to see you're getting there K - keep at it man.
unplug the connectors from the harness and multimeter the shit out of them

Bad Points, a comic :: CB450 Restomod (sold) :: Viragostrosity :: GL1000 daily rider :: Kaw 175

Offline kraptastic k

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Re: "Poor Kid" 1981 CB750K - first build
« Reply #7 on: May 01, 2013, 18:25:24 »
That's terrible criticism Rich! Thanks for the support man. A matter of time now, hopefully only weeks. Damn wiring will be the death of me

1981 CB750K (getting there now)


Offline madd750

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Re: "Poor Kid" 1981 CB750K - first build
« Reply #8 on: May 02, 2013, 00:39:51 »
Keep at it man, it looks like your on the right track and your fixing your problems properly. All the frustration will be worth it once you start riding it.

Offline kraptastic k

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Re: "Poor Kid" 1981 CB750K - first build
« Reply #9 on: May 02, 2013, 00:49:07 »
I keep hearing that. Hopefully I'll get to experience it soon! Figured out some stuff on the wiring with help from a friend and ready to solder tomorrow. Diagrams are making my head spin tonight.

1981 CB750K (getting there now)