1980 CB750F for $180, modern suspension and upgrades for a cafe racer build

I'm about to start wrenching on the CB750F, I got the title for it and now it's getting warm enough to play around. First thing I'm going to open the spark plugs up and get some penetrating oil in there to sit, then take a wrench to the alternator side and see if it turns over.


So my gauges are busted, gas tank rusted to shit, chain is shit, forks are probably shit too, tires are bald, flat, and cracked. All the master cylinders are dry, and the bars are bent. I will be in this for a while and all new stuff getting done. We're going cafe racer, with functionality not just for looks. So modern tires. I'm thinking of a CBR600 swingarm swap, and having my custom shop fab up a rear hoop, as well as a shock mount. What about front ends? GSXR? Or should I keep the factory forks and just rebuild them? If not CBR600 swingarm, what replacement rear suspensions should I look at?

Any other upgrades and advice will be greatly appreciated. The bike is really in bad condition overall, so I'm also thinking of aftermarket master cylinders, can't decide on a eurostyle sport bike bars with factory foot controls, or clip ons and rearsets. I'm going to completely overhaul the carbs with my ultrasonic cleaner, and install K &N pods, mostly because the airbox is damaged and I don't feel like sourcing one on ebay. I'll be having new exhaust put on, the OEM ones detonated from the looks of things, so I want a 4-1 with Yoshimura muffler, something that's quiet and really smooth. I've got two other straight piped bikes and don't care for the noise.

A shining example to chop up and make cool and good again.
Is the motor free, that would be my concern

Keep the pics coming.....and I like the price of the bike!

Pulled the bike out and started a little work. Appears somebody wanted to pull the engine because a few of the engine mount bolts are missing. Whatever. Silicone dribbles on the valve cover gaskets and grommets. Poorly painted. LOL. Anyways, I pulled the plugs out, sprayed my trusty multipurpose spray Ballistol down the holes, and pulled the alternator cover. Ruuuuust. I hooked a wrench up and she turns over! I left the plugs barely threaded and she has equal sounding compression in each cylinder! A little rattle though in the top end, perhaps valves clicking open and shut? Well that's good news either way, I sprayed down the rusty alternator internals and buttoned it back up. Now I'm in the process of pulling the carbs. Looks like someone again attempted some work here but lost some screws. I'll let you know what's what.

Papinbrew, hi there. Nice, good to see what you are doing there. I am in a very similar project. Just to show a pix of my 80 CB750F as it stands. I just had a 10 GSXR1000 front setup done. I am planning on spoke wheels. Front hub from Cognito, rears will be stock hub and Motosyntesis rings. And in that case I will keep 19frt & 18rr on stock tires to ensure a more realistic Cafe Racer look. I am deciding on aluminum wheels yet. Wishing for aluminum tank/seat but it costs a fortune, and no perfect fit for it from India, so I am working on it. So, lets keep working and good luck.

Carbs are out. Dirt everywhere. Carb insulators are garbage. Most shattered and cracked when I removed them. Airbox seems to be in decent shape except the boots going to the carb. Also noticed my starter solenoid was macguivered and the fuse is now a strip of tin foil. Excited to see what other surprises there are.

Didn't take many pictures of the carbs during cleaning. The service manual I have recommended NOT to split each carb body separate, so I left them all as a bank and cleaned the outside with simple green and a toothbrush. There's only a couple spots the toothbrush couldn't reach, but for the most part 95% clean outside. Then disassembled each carb one at a time and dipped the parts in my USC using a pinesol solution. Some were nastier than others and pretty much all required me to use my toothbrush to get spotless. Turns out my floats are plastic non adjustable, and my jets are 100 mains, 68 secondary.. I was able to cut a notch with my dremel in the broken idle mixture screw on #2 to extract it as well. I've got to order up new float bowl gaskets, and a accelerator pump rebuild, where's the best place? I've got a battery on the way as well.

Also, my hand controls are toast. The throttle sleeve is broken and the control module looks cracked in a few places. So besides going to eBay and getting OEM, are there aftermarket controls I can pick up? I'll need new bars, and new controls for both sides as well as a new master cylinder for the brakes.

Ordered a 4x carb rebuild kits on eBay, coming from taiwan. We'll see the differences in the needles and jets, may just stick with OEM needles but at least all the Orings and gaskets are there. $43 for all 4, can't beat that with a stick. The expensive part is the accelerator pump, that's $40, so I'll order that next pay period. I've found some hand controls, handlebars, throttle sleeve assembly, and aftermarket brake master cylinder from Dimecitycycles.com, again probably next pay period. I'm gonna be waiting a while for the carb rebuild kit anyways.

Any ideas whether these will work for my application?

A pair of Black CNC Front UNIVERSAL Streetfighter Motorcycle Brake & Clutch Master Cylinder Reservoir Levers Kit 7/8"(22mm) Fit For Yamaha YZF R6 2005-2012 https://www.amazon.com/dp/B00G20IXRO/ref=cm_sw_r_other_awd_N7ZaxbVASMXNF

Papinbrew said:

Also, my hand controls are toast. The throttle sleeve is broken and the control module looks cracked in a few places. So besides going to eBay and getting OEM, are there aftermarket controls I can pick up? I'll need new bars, and new controls for both sides as well as a new master cylinder for the brakes.

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There is this start/stop throttle control. I'm not sure who makes it, but got one for my project as well. It's also notched on the bottom, so you can feed the wiring outside of the bars, but looks OEM. http://www.ebay.com/itm/151994489489?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I've a feeling you'll be wanting a new charging system soon. Unfortunately, it'll be double what you have in your bike.

J-Rod10 said:

I've a feeling you'll be wanting a new charging system soon. Unfortunately, it'll be double what you have in your bike.

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I have that same feeling too, good thing there's motorcycle boneyards around here, and if it comes down to it I'd buy a new one. Only time will tell!

For $180, you almost can't go wrong.

There should be no noise coming from the valvetrain when rotating the engine by hand. My guess is the last person screwing with the top end has not timed the cams properly and your valves are clashing (and bent or dinged).

Also a possibility that the camchain adjuster is messed up.

Good luck with that.

Papinbrew said:

I have that same feeling too, good thing there's motorcycle boneyards around here, and if it comes down to it I'd buy a new one. Only time will tell!

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I wouldn't buy a used one. That bike is notorious for a weak charging system.

grandpaul said:

There should be no noise coming from the valvetrain when rotating the engine by hand. My guess is the last person screwing with the top end has not timed the cams properly and your valves are clashing (and bent or dinged).

Also a possibility that the camchain adjuster is messed up.

Good luck with that.

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Here's a quick.video of me cranking the engine by hand:
https://youtu.be/jsyHqDk9MDI
Maybe you can help.me figure the noise out?

Too late to stop turning it, which is possibly causing more damage.

I'm not an expert on the subject, so can't direct you to an easy path to the problem.

I just know it's not right.

Sorry.

grandpaul said:

Too late to stop turning it, which is possibly causing more damage.

I'm not an expert on the subject, so can't direct you to an easy path to the problem.

I just know it's not right.

Sorry.

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So it's definitely the valves that are noisy, perhaps the engines been sitting so long the top end dried out and the valves are sticking open then clacking shut? That's all it sounds like to me. When turning the engine over, each cylinder has compression. There's no strange hard spots but feels like I'm turning over my other bikes.

"Have at it!"

grandpaul said:

"Have at it!"

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Lol its pretty early still, are you being facetious?