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Author Topic: 81CB750c build first time here goes nothing  (Read 4280 times)

Offline lostinmiself

  • Posts: 51
81CB750c build first time here goes nothing
« on: Feb 18, 2017, 18:29:50 »
Building my first cafe bike, figured this might be a good way to keep track of my progress and keep things organised if I start having questions rather than posting on each sub as needed. First bike was a cm200t rode that for a season off and on, but really felt like a monkey F-ing a coconut on it (im 6'2" that bike seemed to fit in my pocket). Sold it and was on the search for another bike more my size. Came across this 81cb750 early spring of 2016 and the guy wanted 2900 or something. I sold the cm200t for 1200 and thats what i was willing to invest into another bike. Im very...frugal...to say it P.C., and dont really like to spend more than i have to on things i want. That being said we couldnt reach a deal and i kept looking throught the summer. Nothing really caught my fancy, started to get in to the shitty months and low and behold the same bike came back up for sale. So i got back in touch and worked out a price of $1350. Has 18k and a cam seal leak, 4-2 pipes, other than that bike seems to be in good mechanical condition.



I pulled the rear chrome rack, fender, lights, and on the shelf they go to collect dust, removed the front blinkers as well. threw on some clipons and bar end mirrors and i can start to see where im headed.


Of course i have to hide all the electrical harness, so that was next. While cleaning the garage i came across a skid plate from a 89-98 silverado from an old pickup i sold, as i was walkign to toss it in the trash i happen to get the wild idea about using it as a tray for the harness. Tossed it under the seat on the frame and it was like a gift from the cafe gods! Fits as if was meant to be. Had to notch the front so the harness could fit in to the tray (i probably could have done a better job at it but it was more of a spur of the moment cut, cant see it so im not really worried anyways.



Thats where i am at currently. Painting it so it doesnt rust, but i figured i would make one of these while it drys. I also have some 90s cbr600 coils, and am going to do the resistor mod as well. I picked up a ducati integrated LED tail light i hope to use, seems like the lines would fit well with a tail piece when im to that point. Also plan to use some velocity stacks and if that wont work, ill get a cognito moto filter box. Still need to get a 4-1 exhaust as well im not really digging the 4-2 split style that much. I have some rear sets i also plan to use at some point i need to get some hime joints and get the linkage made. Until then this is the direction i want to build towards.



Cheers!

Offline lostinmiself

  • Posts: 51
Re: 81CB750c build first time here goes nothing
« Reply #1 on: Feb 21, 2017, 19:15:54 »
Finished up the harness tray, threw some rest prevention primer with a black semigloss paint and bolted everything in for a final test fit. Tossed the seat and tank on, looks good from where im standing!
Happy with the free tray mod. Hopefully it works for someone else.


After i got the tray all done, i went to start with the coil relay mod and cbr600 coil swap when i noticed one of the stator cover bolts was missing. After finding a replacement to thread in and continue on with the coils it wouldnt thread in. Got down and noticed it has been broken off, and someone tried to drill it out. I gave it a try with an eazy out and decided to order another one rather than trying to fix it. Found one on ebay for $15 shipped and was good enough for me.



Got to run and grab some spade ends and can get back to the coil mod. Seems easy enough and if the interwebz are correct will help out tremendously.

Still need to order some velocity stacks, but im unsure what ones i want to pull the trigger on, there is a nice set on dime city (http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-carburetor-parts-polished-aluminum-keihin-honda-velocity-stack-cb750-dohc-carbs-pft-sd-cb750dohc-pft.html) im still shopping around to see if thats what i want to get. I know there is steel dragon performance as well, any other vendors make a decent quality stack?

What about shocks what direction do yall think i should look? DCC has a set of universals on sale today for $59 with a weight at 365lbs per shock. That sits at 730lb with a roughly 500lb bike and 210lb rider.
 http://www.dimecitycycles.com/catalog/product/view/id/1831/s/13-2-inch-black-chrome-eye-to-clevis-rear-motorcycle-shock-absorbers/category/1836/?source=hp-daily

Offline BigNickel

  • Posts: 43
Re: 81CB750c build first time here goes nothing
« Reply #2 on: Feb 22, 2017, 10:57:19 »
I'm currently working on a '81 750C as well. I'm really liking what you're doing so far with this bike - I'll be following this build.

What online link did you use for the coil mod? I was also thinking about doing this while I have my bike apart. Also, where do you plan on putting your battery? Some more detailed photos of your harness tray once you get it finalized would be much appreciated.

Cheers.

Offline Cookie

  • Posts: 595
  • God help the child who grows out of everything
Re: 81CB750c build first time here goes nothing
« Reply #3 on: Feb 22, 2017, 11:58:04 »
I used the cb750c forum. An absolute TON of information relative to the 79-82 cb750c on that site. It's run by a group of surly, old guys, but they know their stuff! Here's the link:
http://cb750c.com/modules.php?name=Forums&file=viewtopic&t=2740&highlight=relay+mod
You may have to register with the site to access it, but I'm also going to attach a schematic of how to wire it up.

I used 10ga wire and a 70A relay from a Land Rover air suspension system that I had lying around. You don't need to go that heavy duty, but for me it was a free upgrade. I wouldn't use smaller than 12ga wire.
* Insert something witty here *

81 CB750C
84 Tempter - well, most of it...

Offline teazer

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Re: 81CB750c build first time here goes nothing
« Reply #4 on: Feb 22, 2017, 12:18:01 »
Any modern i.e. new 20-30 amp relay is more than enough.  You can get one form your local auto parts store or on line form places like http://www.cycleterminal.com/accessory-relays.html  I like the 20 amp micro relays and use them for dip and main headlamps and the ignition circuit.

You will be fine with the same wire gauge as the stock system, or even lighter gauge on the switching side and keep the power side from battery to relay as short as possible/practical.  The idea is to stop trying to push all the ignition power through old main switches and kill switches which are really not designed to take that much power, and to reduce the voltage drop through long leads.

Offline lostinmiself

  • Posts: 51
Re: 81CB750c build first time here goes nothing
« Reply #5 on: Feb 22, 2017, 14:09:25 »
I'm currently working on a '81 750C as well. I'm really liking what you're doing so far with this bike - I'll be following this build.

What online link did you use for the coil mod? I was also thinking about doing this while I have my bike apart. Also, where do you plan on putting your battery? Some more detailed photos of your harness tray once you get it finalized would be much appreciated.

Cheers.
I'll get a link up for ya when I'm back on my pc, but basically like they said above bypasses the OE harness and runs a new one for the coils. One lead from power to relay, one lead from relay to coils, one lead from relay to kill switch at controls, and one ground. Remove the power and  ground from the coils and use the new power lead from the relay, and the relay has its own ground. Anything specific photo wise with the tray?

http://gstwins.com/gsboard/index.php?topic=62039.0
thats the link i went off of

Sent from my SM-N920V using DO THE TON mobile app
« Last Edit: Feb 22, 2017, 16:10:42 by lostinmiself »

Offline Cookie

  • Posts: 595
  • God help the child who grows out of everything
Re: 81CB750c build first time here goes nothing
« Reply #6 on: Feb 22, 2017, 14:19:27 »
Any modern i.e. new 20-30 amp relay is more than enough.  You can get one form your local auto parts store or on line form places like http://www.cycleterminal.com/accessory-relays.html  I like the 20 amp micro relays and use them for dip and main headlamps and the ignition circuit.

You will be fine with the same wire gauge as the stock system...

I agree wholeheartedly. I only used the super-duty stuff because that's what I had lying about. I have about a half dozen of those big Land Rover relays. The ignition coils will never pull 70A (the fuse is 15A and the main fuse for the bike is 30A), but I just didn't want to have to buy anything. Same goes for the heavy gauge wire. I had like 8' of it coiled up in a corner of my toolbox, so I figured, 'what the heck'? Perhaps I'll redo it if I happen across a spare mini or micro relay, but for now I'm happy.

The point is, it works.
* Insert something witty here *

81 CB750C
84 Tempter - well, most of it...

Offline lostinmiself

  • Posts: 51
Re: 81CB750c build first time here goes nothing
« Reply #7 on: Feb 22, 2017, 14:30:25 »
Anyone have any experience with Li batteries rather than AGM? I'm going to have to get one or the other, with minimal electronics I figured spending the extra on an Li that's lighter, and smaller wouldn't hurt. Makes it easier to hide as well.

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Offline Cookie

  • Posts: 595
  • God help the child who grows out of everything
Re: 81CB750c build first time here goes nothing
« Reply #8 on: Feb 22, 2017, 14:51:58 »
I put a Shorai into my friend's CB125. Their Li batery is the same as the unit that my 650 Tempter used.
Teressa's 125 has sat outside all of this winter, and in her shed all last winter; still fires up like it's brand new.
Conversely, the 15lb standard lead-acid battery in my '79 750F lasted 3 weeks of non-use in the summer before I had to rush out and purchase a Battery Tender (couldn't justify another battery so soon after the last one).

I plan on acquiring a Ballistic 8-cell for my 750C, once I can come up with the extra $$$
* Insert something witty here *

81 CB750C
84 Tempter - well, most of it...

Offline lostinmiself

  • Posts: 51
Re: 81CB750c build first time here goes nothing
« Reply #9 on: Feb 22, 2017, 16:08:12 »
I should figure out what my idle output will be before I invest in a new battery. I don't want to spend some bucks and ruin the battery with sub standard charging. 13.1v+ seems to be the necessary voltage at idle and no more than 15v at max. I have a good wet battery but of course those don't hide well, and all the work on the tray would go to waist if I had to hang a battery back there. I saw some putting it on the swing arm but I don't like that idea having it connect to moving parts, worst case scenario comes to mind.

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