1980 CB750C Cafe Project "Green Onions"

[Vortices]

Hey all, figured I'd start a build a thread on my new to me CB750C. I bought it non running and stock as hell for 1500 bones in 2021, for an extra 500 the seller threw in some "high quality cafe conversion parts". I was hungover and didn't notice that literally all the parts were cheap Amazon shit. Anyways I started off with a carb clean and some cosmetic work. I had an '81 CM400T which was my main focus as it actually worked.
Unfortunately I don't have any pictures of the 750 before the paint job, frame chop, bar swap, and stock light delete. It's not too hard to imagine though, it was white, crusty, had some lichen growing on it, and had the stock seat.

 

[Vortices]

After spending my time polishing up the CM400 and selling it, and then tackling a full suspension overhaul and upgrade on my Volvo 240 Turbo I finally had some breathing room to work on the hog. I managed to get it running decent enough to get around the block and decided that it was time for some cosmetic upgrades.
I started by using the cheapo Amazon seat as well as the hoop and rear light that came with the bike.
I've always loved the look of older cafe bikes and the small rear cap/fairing piece, so I decided I'd make my own.
I grabbed a piece of the CM400s rear fender I'd chopped off and kept for the duck tail of the rear fairing.

I cling wrapped the seat and, using some discarded fiber glass and carbon fiber from work, got a pretty good shell formed.

I had to add some kevlar strips for some extra rigidity and, after much sanding and priming and sanding and painting, it turned out not too shabby.

For the rear hoop and light setup I glued the light inside the hoop and stuck some reflective gold heat tape inside for extra refraction. I then filled the inside of the hoop with a two part clear epoxy resin and filed and polished it to the shape I was after.

The end result is pretty much what I was after, the only issues with this design is if the light ever breaks I'd need to fully build a new housing as the light is very much encased in resin.
For now I like it.

 

[Vortices]

Over the course of improving the bikes aesthetics I diagnosed the crank no start issues.
My first order of business was a new battery, new plugs, some new gas, and a quick spritz and scrub of the carb bowls, jets, and float valves.
This got her running, not super well, but running.
I then replaced the throttle cables as they were old and gummed up and a quick oil change after it had run for a bit.
The issues continued with the bike, the most prominent being an increase in idle speed as the bike warmed up.
It would start and idle fairly well, but as it got closer to operating temp the idle would increase until it would sit at about 4k when all warmed up. Not great on the ears, and super annoying in traffic.
Yes, I changed the carb boots, no it didn't fix the issue.
After only getting about two months of riding in and maybe a handful of those rides being issue free I decided it was time to try my hand at carb rebuilds.
The nice thing about this platform is that they're super popular so, using a step by step guide off these forums and parts from Randakks, I set off splitting the four carbs apart and tearing them down.

I discovered that basically all of my air diaphragms had tears in them, the float valve seats were gummed up and a bit corroded, the felt seals on the choke and throttle shafts were barely hanging in there, plenty of gas boogers flushed out after the ultrasonic bath, and every o ring was degrading/rock hard.
All o rings, air diaphragms, felt seals, and float valves were replaced with new bits.

All in all I had a great time rebuilding the mechanical computer and I'm very excited to get this thing synced up and running properly.
Attached for your convenience is the guide I used for the rebuild.

https://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

 

[Vortices]

I really enjoyed the cafe bars and the rider position on my 400 so I'm going to try and emulate it on the 750.
If money were no object I would commit to a gsxr fork swap or something but this bike isn't my only project so I had to settle for some cafe bars and dropping the front end a little bit.
Originally I had some flat bars but I felt like I was riding a Harley, hence the swap.

Attached is the before and after, from flat to cafe.

I ran into a couple issues with the new bars, the main one being that the my turning limit stops became the tank and the bars, and secondly the throttle, and clutch cables were now too long.
I solved the turning limits by drilling and tapping the original stops and installing some bolts to find tune where I needed the new stop range to be.

The need for shortened cables was solved by just buying a set of shortened cables after absolutely butchering my first attempt at building my own.
I also opened up both the left and right switch sets and cleaned the contacts thoroughly, my start switch body had a crack in it which I solved with some aircraft grade adhesive and a small piece of aluminium.

 

[Vortices]

I tried my hand at tire replacement and after inventing a couple new swear words I managed to wrestle a brand new pair of Dunlop D404s onto the wheels.
I don't have a balance stand so I took em down to the local shop for the bead seat and balance.

I also took some time to scuff out some corrosion on the rear axle and clean up all the spots that are hard to get to when everything is back on the bike.

 

[Vortices]

I picked up this front fairing off marketplace for cheap, and although I'm not super sold on it I had some free time and extra paint kicking around and it turned out pretty good.

My only issue is that the top edge of the fairing sits kind of forward and gives it an almost "Harley Roadglide-esque" look to the front.

I'm gonna see if I can trim the windshield to make it a little more streamlined as I would like a more uniform classic cafe racer profile.
I even extended the headlight with some aluminium bracket extensions to try and offset the fairing shape.
I'm not 100% sold on the look.
I'm considering just flipping it over and running no windshield.

 

[sergei]

it turned out very well and neatly

 

[Vortices]

Great progress these past few days!
After cranking and not starting she finally caught and idled up great.
I swapped the old plugs out with some fresh ones, and made sure to spritz some wd40 in each cylinder just to aid with lubrication as it hadn't run in about 8 months.
The carbs were completely empty of fuel after the rebuild and I think it took a while for the ACF-50 I had generously added to be replaced with nice, new, combustible gasoline.
I was ready to do a crab sync but it sounded and looked pretty much dead on at idle, so I guess my bench sync was good enough.

I've got two more hurdles and some odds and ends before it's fully on the road. One being checking the valve clearances, the other being a dynamic timing check, but the days of actually riding this thing are definitely in sight!