1981 Honda cb750c build

jonsnibbor

New Member
Hey everyone! Greetings from St Petersburg, Florida. This is my first bike, first build, and first post so be nice but I definitely welcome tips/constructive criticism because I'm definitely not as mechanically inclined as many of you are. Here goes:
I got this pic from a google search but mine was almost exactly like it when I got it, just not as shiny.
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It ran decently, the only thing I had to do was make it look like this:
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It can't be that hard, I thought. If only i could go back in time i would have slapped myself. First things first-removed the extra stuff, windshield, seat rest, side covers, rear fender, etc. Probably dropped 50 pounds right off the bike. This next pic is after I had done a bit of messing around...I had taken off the chainguard, replaced the sprockets and chain, painted the rear wheel (supposed to be flat black but turned out really dark green for some reason? I'll have to redo it) and also discovered underneath the vinyl that the seat foam and pan were moldy and rusty. Pitched it in the trash, I'm planning on making a fiberglass seat. Also, I know the jack looks very unstable here, I fixed it right after i looked at the picture. I had put the pods on before I read how ineffective they are, so I'll be messing with them later. Planning on rejetting and putting on K&N pods, if anyone has any specifics on jet sizes that would be very helpful! Oh I also took off the bulky four way exhaust. I got a four to one exhaust from carpy that I wrapped but i forgot to take a picture of it. I had to take it off to use this jack. i had also replaced the rear springs-used the old suspension set but put new progressive springs in. Much better!
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Took the carbs off to clean. I found it to be really difficult to get the carbs off the boots-had to use a tie-down from my old truck to wrench the things off.
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Cleaned them out, they really werent too bad though.
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Tore into the front end. Here I had painted the headlight that nasty dark green color, it clashes pretty bad with the black frame so I'll be redoing it. Also sorry the pics aren't great, taken with an old ipod.
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Planning on hiding all the electronics somewhere...most likely under the seat I'll be making.
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This was a fun day. By the way I live in an apartment...doing all this on the front porch is not ideal. trying to not piss the neighbors off too much.
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Taking the forks apart was a real job. I needed to replace the springs and seals but popping those seals out was really tough. Ended up filling the tubes up with water and using a long pipe clamp to compress the fork until the seal came out. Ended up shooting oil all over the place but hey it worked.
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New springs.
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My ghetto set up for painting the front forks. Flat black, will clearcoat with spraymax 2k satin.
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This is the front fender, decided to chop it down a little. Covered it in tape and drew a line where i wanted it cut the used an angle grinder to make the cut.
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More angle grinder fun. I love cutting off dead weight from the bike. I removed a bunch of tabs that I won't be using and also the nasty old center stand. Probably lost another 8-10 pounds there.
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New (old) tank I got on ebay for 70 bucks. It has a little rust and needs some bondo on the outside but I really like the shape of the tank. Its from a 1982 CB750f Super Sport. The gas tank mount on the frame is too far forward for this tank so I had to cut it off, add some steel to either end of the mount (had to learn how to weld-got a cheap welding box from harbor freight for 100 bucks-its working decently) and weld it back further. My welds dont really look too great but they are pretty strong, and its not really too crucial to the bike's structure so I'm not worried.
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I know, I know, the welds look pretty bad but I promise you they're strong!
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I was nervous to do this. No turning back now!
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The pieces I cut off.
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Thinking about welding them back on like this to make the shape for the seat. Opinions welcome!
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As she stands today:
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What do you think? Digging the tank swap? I am.
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First off, WELCOME! nice to see these DOHC 750's gaining popularity. There is a thread here strictly for those of us who have them, do a search and join in the fun. ;)

Now comes the "help", you are going to get mixxed reviews on running Pods with those stock carbs. Many have tried, few will say they succeeded, and I venture to geuss even less actually did... real can-o-worms for even experianced builders. Hold onto the stock airbox so you can go back to it if needed. Do NOT join www.cb750c.com and ask questions with those pods, they will beat you to death with your own keyboad. :-X

If your insulators were so hard that you had to ratchet strap the carbs off, get a new set. Less chance for vacuum leaks with new soft ones. I got mine from http://www.vintagecb750.com/

What was the reason for cutting off the rear frame horns? Are you planning on welding in a hoop? That cross member behind the rear shocks was there for strength so you ought to tie them together somehow.

Do you still have the factory 4-4 exhaust? If it was in decent shape, they get a good price on ebay that will help fund your build.

Read up on the valve adjustment procedure. You will want to check that and get the shims sorted out before you get it all buttoned back up. Probably THE biggest cause for poor perforamce on these bikes.

Even though it was originally a cruiser, being your first bike, once you get this bike on the road if it doesn't scare the Bejeesus outta you when you grab a handfull of throttle, it isn't running well... ENJOY!
 
i add my welcome

and this test your charging system and make sure it is working properly

before chasing any other gremlins if the charging system is not right the ignition can be unstable
 
Hoosier Daddy said:
What was the reason for cutting off the rear frame horns? Are you planning on welding in a hoop? That cross member behind the rear shocks was there for strength so you ought to tie them together somehow.

You know, I wondered about that before I cut off the back part of the frame but decided that the brace right in front of the shocks would prevent any lateral movement of the frame. It feels very sturdy as is, do you think I should add a cross member to reinforce the area? And the reason i cut off the frame horns is to change the shape to an upward curve-I like the more aggressive looking stance.
 
my opinion is anything behind the shocks is to take the loads of a possible 220 lb+ passenger,for solo riding you will be fine, i would bet money onnit
 
Welcome!! If you don't weld on a hoop you'll definitely need a brace inline with the shocks. You'll get some kind of twist going on there when cornering otherwise. ps its looking great so far, as for the tank I would have swapped my square one for your round one any day:)
 
Proof that your advice doesn't fall on deaf ears! Welded on a brace and flipped the rear horns upside down and welded them back on to begin making the shape for the seat.
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You my friend...are a star!

I have been looking high and low to see if a CB900F tank would fit on a Custom. Finally!!

Check out my project, which with your help....will soon have a CB900F tank!
http://www.dotheton.com/forum/index.php?topic=53313.msg600123#msg600123
 
Thanks! You can definitely make the tank work. The front of the tank was a little too tight of a fit so i trimmed the rubber stoppers on the frame down just a tad and then it fit perfectly, the only real adjustment you would have to make would be the rear mount on the frame. I have absolutely no welding experience and I found it to be not that bad of a job. Just chop the mount off and move it back a few inches and voila. I'm with you man, I dig the look of those F tanks a lot more than the teardrop C ones. BTW I just checked out your build and it looks awesome so far! I'm digging those handlebars...I'm thinking I might get the same thing actually. Where did you get the two plates that screw down over the handlebars?
 
They are the stock mounts. Trying to source a new upper tree though, as its a bit far back for my liking


Any places to lower the front forks??
 
Bare in mind jlawie that yours is a CB1000C and jonsnibbor's is a 750.
Don't know how much different the two frames are but obviously some, the litre bike is a shaftie...
 
Tanks are the same between the 750c, 900c and 1000c. So mounts will match.

The 900 and 1000 have a longer back end from the gearbox backwards.
 
Okey Dokey... just thought it worth mentioning about the frames.


81 CB750C tank part # 17540-MA5-670**
83 CB1000C tank part # 175A1-MG1-000**
 
HD has given you some good advise there. I like your ingenuity regarding the forks, but its usually easier to remove the stanchions from the lower legs to remove the seals. Good to know about the tank, I was always interested to know if the custom tank would fit on the F frame.
 
jlawie said:
Tanks are the same between the 750c, 900c and 1000c. So mounts will match.

The 900 and 1000 have a longer back end from the gearbox backwards.

Was going to comment then realised you said C models, so I'll keep my mouth shut.
 
Hoosier Daddy said:
Okey Dokey... just thought it worth mentioning about the frames.


81 CB750C tank part # 17540-MA5-670**
83 CB1000C tank part # 175A1-MG1-000**

As far as I'm aware, the only difference is the petcock thread
 
It can be a bit of a minefield relying on part numbers to identify parts compatibility as the same physical part could have different numbers just for a colour change especially thing like tanks and bodywork. I know some ZX6r and ZX9r fork lowers are the same but have different part number because they are different shades of grey.
 
jlawie said:
As far as I'm aware, the only difference is the petcock thread

Yes, thats something I found out the hard way. That's the only difference I have found between the two tanks. I say go for it jlawie, get a tank off of an F model and post pics for us! And don't kill me if it doesn't fit.
 
jonsnibbor said:
Yes, thats something I found out the hard way. That's the only difference I have found between the two tanks. I say go for it jlawie, get a tank off of an F model and post pics for us! And don't kill me if it doesn't fit.

Got a K tank on route. From the dimensions weve checked, it should be a straight fit.

Fingers crossed!
 
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