DOHC cb750 mono shock cafe build

First off, I'll get the obligatory new guy intro out of the way. I picked up an 82 cb750 almost a year ago for a a project since the garage was lacking one I'd those at the time. Gave 300 bucks for it, nothing special just an old bike somebody got to fix up and lost interest in. The original plan was to build a hard tail cafe/bobber kind if thing. This was my inspiration

Got the bike home and started pulling all the non essential stuff off, headlights, gauges, seat, ect, cut the subframe off and I was left with something along these lines

At this time in the life of the project it was kind if a work on it here and there thing. Want real sure how I wanted it to turn out, waiting on deals for the parts I knew I would need like usd forks and wheels, had other things going on, and looking for ideas. Well between looking for ideas and talking to a few people I decided to not hard tail the bike and build a mono shock cafe racer since I had a mono shock from a k1 gsxr 1000 that I bought wrecked for the engine and I had found done pretty mean looking cafe racers out there. Fast forward to about 2 months ago, I laid my other bike down in the north Georgia mountains, totaled it and was bikeless. So that meant it's time to really get a move on this build. In that time frame I had modified the factory swingarm with new non adjustable axle plates that a buddy of mine cut out on a laser table, built a set of dual carb manifolds since I couldn't find any commercial ones that would fit like I wanted (they may work they may need some adjustments and they may need to be completely rebuilt). Sadly I didn't take many pictures of those parts. Since I also had a freshly totaled 08 gsxr (went over the edge the front wheel hit a tree and it peeled the neck away from the rest of the frame, surprisingly though the forks were still good) sitting in the shop most of my waiting for deals on parts problem was solved. Rearsets, usd forks, brakes, rear wheel. Now that the build is moving along a little quicker now I figured I've been lurking here for ideas so why not actually join the forum and start a build thread. This is the bike as it sits right now. I'll update add I go and try to not get carried away building remember to take pictures. Hopefully this turns into both a decent build and a decent thread. Enjoy.

I lucked up and found a tank I liked this weekend which meant that now I can get my seat hoop mounted since I wanted to keep the lines on the tank and seat hoop even. The front end is just stuck on there at the moment with no bearings in the stem. Im going to have to spend some time on a large at work to make a steering stem for them. Front end and wheels are off my wrecked gsxr.

Working on a 81cb750 my self, posting to watch what you do for some inspiration. I like the 2 in to 4 carb setup that. Does it run better with that?

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I'm not sure yet. I got it running before I tore into it but haven't messed with the dual carb setup much since I got the manifolds done. I'm doing it more for the look than performance but if it's much more than a minor downgrade I'll probably ditch it in favour of something else. I've been debating a single carb with small turbocharger but I want to get everything else roughed in first so I can see if I'll have room

I've also got an 81 and a turbo is on my list of future things to do as well. Nice build man, but how do you adjust chain tension with fixed axle plates? Gonna run a tensioner on the swinger?

Interesting.

Yeah I've got a few ideas bouncing around in my head for a chain tensioner. When I did the axle plates I was still planning a hard tail shoo a chain tensioner wouldn't have been a big obvious THING. Now that it's more of a cafe build the one I was planning on building seems a little big for the look I'm shooting for. Gotta figure out a smaller more discrete tensioner

Did I miss something? Why do you think you need a chain tensioner?

hillsy said:

Did I miss something? Why do you think you need a chain tensioner?

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He can't adjust his axle anymore.

You can get a Comstar to spoke conversion done on the original wheels. Spokes are the way to go IMO.

lostinmiself said:

Working on a 81cb750 my self, posting to watch what you do for some inspiration. I like the 2 in to 4 carb setup that. Does it run better with that?

Sent from my SM-N920V using DO THE TON mobile app

Click to expand...

I could never get that kit to run properly on my bike. It comes with radiator hose as isolators. The damn things bounced around everywhere. Tore a couple pairs of them from the carbs bouncing. Had a carb bounce out of one. Switched to Murray's Carbs kit. Fits in the stock isolators. Fits inside the frame instead of in your knees outside of the frame. And run spectacularly.

Spokes are the end game wheels. Right now the gsxr wheels are on there to get it on the road and because I had them


I'm using hydraulic hose which is a lot stiffer than radiator house. The problem I ran into with any of the shelf kit was that our put the carbs to far back. When I cut the frame I didn't have enough room to fit a carb and a filter

OldandBusted said:

Spokes are the end game wheels. Right now the gsxr wheels are on there to get it on the road and because I had them


I'm using hydraulic hose which is a lot stiffer than radiator house. The problem I ran into with any of the shelf kit was that our put the carbs to far back. When I cut the frame I didn't have enough room to fit a carb and a filter

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Yeah, you're running a much different mono set up than mine. I wasn't a fan of sticking the head of the shock directly to the backbone. Lot of force that frame isn't designed for, and more bracing required than I cared to do.

I went with something that put all of the force into the subframe I build. I know it can take the stress, and with the linkage set up on that particular shock, the top brace is merely a pivot point between the linkage rod, linkage, and the shock being pushed downwards when it compresses.

I'm actually nut directly mounted to the backbone. I'll post up a picture of how I worked it. I didn't like the idea of going directly to it either.. Basically what I did is when I cut out my subframe I cut it all the way up to the 2 "rib bones" , at least that's what I would call them, to keep then from pulling together I put a piece of DOM there and gusseted it. My brackets are wrapped almost 3/4 of the way around that tubing. It may not be what a Honda engineer would call production worthy but I feel pretty good about it.

This is before I added the gussets and shock brackets

omgwtfbbq! said:

He can't adjust his axle anymore.

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Ahh - I see now.


Would be far easier to cut some slots in the axle plates and add some adjusters there. Would only need about an inch or so.

It would be a lot easier to make the axles adjustable. I made them to be non adjustable because to me a non adjustable axle plate gives a bike a super clean look

I'll go ahead and warm anybody that's following this thread that I've got a bad habit I'd jumping around from one part of a project to another. Working on one aspect for a little while, stopping that and moving to something else, and so on and so forth. The last couple of days I've been working on my seat.

To begin with I laid out where I wanted to position my electronics in the tail hoop. I skinned the bottom side with a piece of 22 gauge sheet metal shoo that I would have a place to mount my fuse box, ignitors, regulator and a couple of relays. Once that was done and I was happy with the pavement I'd everything I taped over it with blue painter's tape. I added a could I'd strips of thick cardboard on top of everything that stuck up past the 1 inch tubing I used for the hoop in order to give me a little more clearance between the electronics and the fiberglass seat base. Once all that was laid out like I wanted I covered it with tinfoil and car wax shoo that I wouldn't spend the next week picking blue tape out of the fibreglass. Laid a couple of layers of glass and came out with a nice base to build my seat on. It was a little too cool for the resin to set up so I had to warm the area with a heat gun. It just so happened that the tank habe my the perfect able to heat up the whole thing

what is that green tank off of?