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Project Nashi, Dream of Neo-Tokyo - '79 CB750K Z

945 Views 33 Replies 5 Participants Last post by  Rollen, 
Rollen
I did a thing. I have a '79 CB750K Z, it was under my $1000 budget, it was the only bike in my area with a title, ran in the last decade, decent body and not molested to hell. It's not café racer build, I have no idea what category my build is gonna fall under. My goal is to go OEM+ initially, that means weight reduction, swap OEM parts with better performance OEM parts or noteworthy tried and tested aftermarket parts.

History on the bike:

Have the title clean and matches up with the frame. Engine does not match the title so it was already replaced once before. Previous owner was not mechanically inclined and he was planning to turn it into a cafe racer. He removed the chain because it was hard to roll up into the garage. Owner before him had it sitting with the carb off and reported it had a leak. Signs of when it was last ridden is from a 2017 NY inspection sticker. The spring on the brake pedal is also broken, but owner provided me with a new one. The throttle grip is not installed with cable loose and grip not functioning.


It's in relatively good shape, but I don't believe it's a candidate for a complete resto, since the engine has already been replaced. I would rather do a resto-mod to improve on the platform and eventually stylize it to my bias interest in all things cyber punk/neo-retro.

Below are lists broken out between must do this year and wish list after the must do.

Goals to produce an MVP:
  1. Electric
    1. Replace Battery
    2. Test spark plugs
    3. Clean and test spark plug wires
    4. Replace spark plug wire boot
    5. Replace cracked ignition coils
    6. Replace positive starter cable
    7. Replace broken and work out connector plugs
    8. Install new rubber relay solenoid mount
    9. Replace broken tail light
  2. Fuel System
    1. Drain current gas and check oil levels
    2. Fix #2 carb leak (found replacement bowl)
    3. Clean carbs and assembly pieces
    4. Replace worn out broken throttle tube
    5. Replace all fuel lines
    6. Install air box with new air filter
    7. Install breather box with new vacuum hoses
    8. Calibrate carb off bike
    9. Install carb
    10. Replace broken start/stop throttle switch assembly
    11. Gas tank rust treatment and sealing
  3. Engine
    1. Oil and filter change
    2. install new crankcase breather hoses to air box
    3. Diagnose existing chain and sprocket, came removed
    4. Clean and install drive chain
    5. Diagnose oil leak between cylinder head and valve body (still learning the names so I'll update this if I'm dead wrong on the part names)
    6. Clean engine and polish chrome pieces
  4. Brakes
    1. Repair pedal brake
    2. Replace pedal brake light spring
    3. Replace brake fluid
    4. Replace front break pads
    5. Clean Rotor
    6. Check/Replace rear break shoes
  5. Steering and Suspension
    1. Replace front wheel bearings and gaskets
    2. Clean and polish front wheel
    3. Replace rear wheel bearings and gaskets
    4. Clean and polish rear wheel
    5. Replace steering column seals
    6. Clean and polish fork
    7. Replace oil in fork
  6. Body Repairs
    1. Add missing mirrors
    2. Repair dents in gas tank
    3. Replace seat cover with replica cb750k seat cover
    4. Add chrome trim to seat
    5. Clean and polish fenders, grab bar and chrome trim
  7. Ride the bike and see what else comes up mechanically

Goals after MVP (Wishlist):
  1. Research and replace/refinish gas tank
  2. Research and replace/reupholster seat
  3. Replace rear fender to allow for flush mounted tail light/turn signals
  4. Research into what wheel, fork, and rear drive train combination will produce less weight, better braking and more modern options to bolt on.


Note: I welcome all criticism and suggestions, I'm not here to build a cafe racer, I'm not a welder and I'm not a machinist. I'm very resourceful, I can read, diagnose and troubleshoot complex issues. I'm OCD when it comes to research and just would like a place to speak to others that get what I'm doing because I don't have some one in person to lean on. I can admit when something is outside my skill range. However I'm willing to learn something new, even if it means welding.

Personally I would rather maintain the frame as is, because I personally do not trust a frame that has been sawed and rewelded outside of OEM factory spec or high professional grade.
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TrialsRider
Forks?
Your bike is heavy because everything is steel, replace steel parts with aluminum parts and the bike will be lighter. Your footpegs, centre stand, side stand, fuel tank & rims predominately. The headers will be double walled steel. Your brakes and suspension components are good candidates for replacement. Don't go lower then flat bars or it will be a bear to ride and don't reduce the cornering ground clearance because they can drag hard parts as is.

Carb leaked because it had a stuck or leaking float/needle&seat , might be rubber parts.
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Dan Boy
I love these old Hondas. I owned a '82 FB for 20 years as a stock bike and I loved it. No need to change from stock unless you want to change the look. I also have a '68 Triumph TR6, the brakes are poor on that but you just ride accordingly and get used to their limitations.

Looking forward to more updates.
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Rollen
7
Thanks for the encouragement and advice guys. Here's an update on where I am with pictures. Let's start with the Carbs

Carburator:

Below are shots of the carbs and the pieces I received for them. I reckon that I'm missing many more pieces and the most important being the air collector. I read up and down on the Internet and it seems pods are not the way to go and the previous owner may have been running them or planned to.

What i will be doing instead is hunting down all the air collector parts to get a baseline start for the OEM feel and what the engine should feel like when running correctly.

Note: they aren't opening right and not secured together. Get the sense this was hastily put back together... Either way a clean and a thorough analysis is needed...

Wheel Automotive design Motor vehicle Rim Engineering

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Wood Tool Hand tool Hardwood Metalworking hand tool


Note: missing the entire air collector in the picture below. Using the diagram to hunt down all the missing parts... Would appreciate if some one knew where I can get repros.


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Battery:
Bought an AGM battery, test fitted it and of course terminals are on the wrong side and a bit too lose in the cage. Will have to get a different battery and figure out how to secure it so it doesn't rattle.

Automotive tire Hood Motor vehicle Tire Wheel



Throttle:
Issue with the throttle is that the plastic has broken off the control switch where it screws in.. will need a new one or replace with used one. Whichever is built better...

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TrialsRider
Part 7 or 8 is the intake stack part that will make or break the tune on the carburetors. The top half of the carbs is likely just fine if they still hold vacuum pressure. The carbs will look something like this inside:
Motor vehicle Automotive lighting Hood Automotive tire Audio equipment

If it's all green like that inside it's from copper leaching out of the brass parts. This bike ran after the carburetors were just cleaned and reassembled with all the original parts.

You're going to want access to a motorcycle salvage yard for any parts the previous owner short changed you.
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TrialsRider
The carburetors did not need to be disassembled much beyond what you see in the photo above because all of the problems were fuel related and confined to the lower half of the carbs plus his air filter was shot. Brake master cylinder required rebuild on the CB I serviced that looked much like yours, the front brake didn't operate until about 80 bucks worth of parts were purchased from my nearest Honda dealer.
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TrialsRider
By the way, wheel bearings are relatively cheap for this bike and available from any bearing supply store, replacing them will improve the bikes handling and braking immensely as they are almost certainly the original parts.
lol might even make the pig slightly easier to push around in your garage.
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Rollen
@TrialsRider thanks bro, lots of great info. Going to find a yard and start getting acquainted with them lol
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TrialsRider
Rollen said:
@TrialsRider thanks bro, lots of great info. Going to find a yard and start getting acquainted with them lol
Click to expand...
Guys that own motorcycle shops and scrap yards ride motorcycles, ride with the shop owners and you will never have problems finding parts :geek:
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Rollen
6
TrialsRider said:
Part 7 or 8 is the intake stack part that will make or break the tune on the carburetors. The top half of the carbs is likely just fine if they still hold vacuum pressure. The carbs will look something like this inside:
View attachment 107711
If it's all green like that inside it's from copper leaching out of the brass parts. This bike ran after the carburetors were just cleaned and reassembled with all the original parts.

You're going to want access to a motorcycle salvage yard for any parts the previous owner short changed you.
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I didn't understand if the green is good or bad from your comment. It seems it's bad because only one of them are green. Also carb #2 the float has a bounce when I poke it and the other three have no bounce at all, just a slow rise.

Auto part Machine Engineering Gas Audio equipment



Also found that #2 has a solder repair. Not too pretty but don't care if it's holding. Will have to test them all for leaks.

Automotive lighting Hood Motor vehicle Bumper Automotive exterior


Better shots of the plates

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Reflex camera Camera accessory Digital camera Camera lens Point-and-shoot camera


Gasket seems okay but i honestly want to just buy new ones for peace of mind. The green one has brown crust everywhere so maybe it needs a new one.

Found these two kits not sure which to get though... I like that the second one has all the gaskets and new screws, but first one brings all brass pieces...


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Rollen
2
Air cutoff valve is crusty with what looks like corrosion and tiny o ring is not very flexible.

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Accelerator pump is boogered up.

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Rollen
2
I got issues have all four carbs separated and missing pieces. The thicker shorter tube between 1 and 2 was missing, the compression springs between 1 and 2 as well as the spring between 3 and 4 are missing... The screw that holds the brass T is missing...

Seriously the last person who worked on this took it all apart and then just gave up and didn't bother to put it back together properly.

Automotive tire Automotive lighting Rim Wood Motor vehicle


I found the missing tube on ebay and I also found a full carb screw kit. However I can't find the springs highlighted in red below. The part number for it is 16051-413-004, but cannot find it on eBay or Google... Any help y'all can provide on this will help big time.
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TrialsRider
Rollen said:
I didn't understand if the green is good or bad from your comment. It seems it's bad because only one of them are green. Also carb #2 the float has a bounce when I poke it and the other three have no bounce at all, just a slow rise.

View attachment 107724


Also found that #2 has a solder repair. Not too pretty but don't care if it's holding. Will have to test them all for leaks.
Click to expand...
The green is corrosion that happens when fuel is left in there to evaporate over a long time, it is worse on #1 carb because the bike was left standing on the side stand. Yours is not bad or it was cleaned up some when the previous owner messed with it. The repaired tube is the over-flow tube and if that leaks it will continue to over-flow all the time.

#2 has an accelerator pump that likely operates on deceleration, so the engine returns to idle smoothly. The 'bounce' sounds like it is coming from the needle itself which likely has a spring inside it and it sounds like you have 3 of those that are unhappy.

Used carburetor springs should not be a problem to find at a wreckers, they have hundreds of dead carburetors. If you are buying used carbs off a traverse 4 cylinder motorcycle, buy the carburetor that is on the opposite side from the side stand for the same reason as you see above, #4 might be in a little better condition.
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TrialsRider


Your fuel needle is the at the top left with the black rubber tip, the wire at the opposite end to hangs it on the floats and the tiny brass rod that protrudes just blow the wire clip is the spring loaded part that makes your floats do the bouncy thing.

The tube with the tiny holes in the side is the emulsion tube and that is the part that needs to be microscopic clean.

The function of the larger spring is just to prevent the jet needle from from vibration movement on the threads after it is adjusted.
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Rollen
TrialsRider said:


Your fuel needle is the at the top left with the black rubber tip, the wire at the opposite end to hangs it on the floats and the tiny brass rod that protrudes just blow the wire clip is the spring loaded part that makes your floats do the bouncy thing.

The tube with the tiny holes in the side is the emulsion tube and that is the part that needs to be microscopic clean.

The function of the larger spring is just to prevent the jet needle from from vibration movement on the threads after it is adjusted.
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Thanks bro, that helps understand what I'm looking at. I'm creating a shopping list of things I'll need that are missing. I was fortunate enough to have my buddy recommend a shop that is willing to help me out with missing parts. I'll bring that list to them and also have them remove dents from my gas tank and seal it.
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TrialsRider
Gas tank liner is great if you plan to sell the bike, it's not a forever fix.

With labour costs what they are a new old tank might be a better investment and if that tank is made of aluminum it will last more then a life time without failure.
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TrialsRider
sidenote on accellerator pumps: they are put on there to fix a tuning problem, if it is activated and pumps when you let off on the throttle it is a deceleration control and if it pumps fuel when you open the throttle it's a regular accelerator pump, ymmv.
... either way all it has to do is squirt a tiny bit of raw fuel into one of four carbs that don't share a common intake manifold and it's not needed on all the carbs, so it's function will be subtle.
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Rollen
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TrialsRider said:
Gas tank liner is great if you plan to sell the bike, it's not a forever fix.

With labour costs what they are a new old tank might be a better investment and if that tank is made of aluminum it will last more then a life time without failure.
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The tank has only two minor dents but it definitely needs a paint job. I don't want to buy the tools to repair the dents since I won't ever use them again. I was thinking of having a shop remove just the dents. I'll refinish the paint because bottom is hiding some rust and some one tried to cover it up.

Inside is really nice though and just needs a good soak in vinegar and then sealed. Some one may have already treated it in the past.

Carb #2 failed the leak test. The base has a slow leak and the shaft of leaks worse despite some on else's attempt to seal it. The shop keeper I've been talking to is hunting down a new bowl and the two springs.

Hood Motor vehicle Automotive lighting Trunk Automotive exterior


I went through all of the carb parts and diaphragms are all shot and need all new gaskets. Buying quality made in Japan stuff but won't pull the trigger on the shopping cart till later. Waiting on whether I'm gonna invest in a ultrasonic cleaner first.


At the moment I'm restoring an old pot sand blaster my uncle gave me. Going to use it for soda blasting the parts.

Road surface Asphalt Line Drink Sidewalk


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In parallel I'll check out the sparks, front brakes and install the new start stop switch assembly and do an oil change. Looking forward to hearing it run!
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Rollen
Had a good two hour conversation with the bike shop owner near me. Awesome guy really knows his stuff at Cycle Madness in Belvidere NJ, very passionate too.

Helped me find a new carb bowl for #2 and two springs. Have most parts except for new screws (couple stripped), drain screws, gaskets and other parts with rubber.

In the mean time I checked spark, plugs looked good but got nothing for sparks. Looked at the coils and they are cracked. Probably the original coils it came with. Going to order new Rick's ignition coils.

Tire Wheel Automotive tire Tread Wood


I have the sandblaster pot almost stripped and replaced most of the bad fittings. Will have it painted and running this weekend. I'll also soda blast the carb parts. Debating on whether I should get a ultrasonic cleaner or if soda blast with a soak will be fine.
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TrialsRider
Ultrasonic cleaner and soaking isn't going to do much more then a can of carburetor cleaner can do in seconds. You are already replacing most of the parts that would benefit from sonic cleaning. I'd put that money towards your new ignition parts.
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