79 CB750K New here

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79 CB750K New here

Ba5sKing
Hey everybody,

Been slowly learning as much as I can about bikes and one of my many frequent google searches to learn more about my dear CB brought me here. You all seem like a great bunch of bikers to know, so figure I'd hang around. Anyway this is my ride my old man gave to me a couple years ago, and im slowly giving her the maintenance that has been neglected for many years. Having issues with the motor right now, but hopefully I can resolve those before the end of the month.

-Ba5sKing

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Re: 79 CB750K New here

Hoko
Welcome!
78 CB750F3 Super Sport
Austin, TX
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Re: 79 CB750K New here

shinyribs
Administrator
Welcome in bud!

Awesome picture! Looking forward to seeing you bring this one back to life. Good luck and keep us posted.
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Re: 79 CB750K New here

Ba5sKing
In reply to this post by Ba5sKing
Hey guys,

So I've replaced tires, brakes, chain, lubed up swing arm, part of the brake calipers, and other random parts. Also replaced filters, and rebuilt my carbs(ill put up pics later). Prior to ripping apart my bike, I was hearing an odd machining like sound coming from her when I would rev it past 2200. Quiet at idle however, my guess is that the timing chain needs to be tensioned or replaced, has anyone ever come across this symptom before? and for the life of me I can never remember what kind of oil a cb750 should have..anyone mind sharing that info too.

-Ba5sKing
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Re: 79 CB750K New here

TOOLS1
Administrator
The cam chains on the DOHC engines will come loose, and eat the engines when the tensioners wear. As for oil 10W 40. I like Texaco Havoline, and change it every 3K miles.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
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I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
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It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
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"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: 79 CB750K New here

Ba5sKing
Hey,

Last night I finally put everything together on the bike, however the carbs leak gas like no other, when I took them apart none of the gasket material was torn so after I cleaned them out I assembled the carbs with the same gaskets. Is it possible that the seal is compromised over time and opening it would cause the gaskets to not seal properly anymore? The more likely cause I would imagine is that the floats are not cutting off the flow of gas to the carbs as they should. Are all the DOHC carbs have adjustable floats? If they do, approximately where is the adjuster and how should I go about this? I only removed the pin that floats revolve on and the floats and needle that is slipped on the floats when I was rebuilding the carbs. Would any of those actions throw it out of adjustment?

Thanks for any suggestions/help,
-Ba5sKing
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Re: 79 CB750K New here

Hoko
This post was updated on .
Inspect your float valve seats, if they are dirty looking, polish them with a qtip and chrome polish.  I like to use a drill to polish mine. I clean them with the Qtip and polish and buff them with a thin piece of rag over the Qtip.  If they are pitted, I've heard you can lap them with qtip and toothpaste, (never tried it).  Dirty valves will leak and cause fuel levels to go into the overflow tubes.  Also you should install new needles with the same kind you have.  (all brass or brass with rubber tip)  Yes, your floats are adjustable.  you bend the small metal tab that pushes the needle whatever way you need to adjust it.


The setting for your carbs is 15.5mm

That setting on the diagram of 14.5 mm is for my carburetors in a 78F, yours is 15.5.
After having done all that,  the only thing I know of that will consistantly cause carbs to overflow is very small particles of rust or debris in the gas tank and not having inline filters installed in your fuel line.  You may have to pull that tank and clean it really well and flush your entire fuel system.
If you have rust, check this out.  Looks like it works pretty well.  http://www.xs650.com/forum/showthread.php?t=30
78 CB750F3 Super Sport
Austin, TX
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Re: 79 CB750K New here

shinyribs
Administrator
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Re: 79 CB750K New here

Ba5sKing
In reply to this post by Hoko
Hey,

Pulled an all nighter last night after work, (buddies have a planned ride this upcoming Saturday). Originally carb number 2 became soaked all around and dripped from the lowest points, not through the overflow route. I was unsure what would happen if the floats were off or if the gasket was bad...after letting the gas evaporate and re attaching it to the tank multiple times to diagnose the leak through what appeared wet, I noticed that it was getting wet above the bowl...I did not remove any of the carbs from the bracket when I cleaned them, I am thinking some of the carb cleaner got in the fuel 'rail' and deterioted one of the o rings. Went to my university and put o rings in last night, now I am getting the symptoms of an overfilled bowl in carb #1. It flows steadily forever through the overflow channel. I will definitely try your suggestion today when I get home, considering I was starting to run out of ideas you are a god send this morning haha. I think I will clean where the needle sits and adjust the float just a tad, I am not exactly the most careful mechanic when I am working..could definitely see the tab on the float being bent a tad.

Sorry I haven't posted any pics yet, they will be up eventually!

Thank you,
-Ba5sKing
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Re: 79 CB750K New here

Ba5sKing
Also, my primary chain is very old and over stretched..I want to replace it, and tried ordering parts through old bike barn, however they said it is not possible to just order one based on my bikes info..apparently it is common to change the ratio of the sprockets to fit a lighter chain. I believe chains are stamped with what 'series'? they are, and mine is way too rusted to read anything. Is there way either based off the sprockets or the physical chain links that I could tell what kind it is?

Thanks again,
-Ba5sKing
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Re: 79 CB750K New here

Hoko
I don't know if you have noticed but there are download links for Factory Service Manuals for our bikes at the top of the webpage.  The manual for your bike is there.
78 CB750F3 Super Sport
Austin, TX
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Re: 79 CB750K New here

Ba5sKing
Hey,

Yes I did notice that and downloaded it earlier, it is a huge help with identifying parts and assemblies on the bike, however lacks solutions and is missing details for certain situations.

So the bike finally idles, I had replaced the cover to the pulse generator and therefore needed to re time the ignition, I also re adjusted all my pilot screws in the carbs back to factory, and slightly increased the throttle, now it starts with no assistance. Does anyone have a good suggestion for getting the bottom rear lock nut for the timing chain? I think I can loosen it via an open wrench, but I don't feel that I will be able to tighten it properly with such cramped space.

I haven't ridden in awhile, but how long should it take around 3,000 RPM's to get too hot to touch? I have an uneasy feeling that my bike is heating up way to quick now, and this morning a good amount of smoke slowly started appear as I was tensioning the timing chain..I was only able to get the front and top rear adjusted before I shut off the bike due to the amount of smoke. Part of me is hoping that I have an insignificant oil leak somewhere causing this qualitative problem, but I never find an oil stain under the bike.

Thanks,
-Ba5sKing
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Re: 79 CB750K New here

motogrady


Air cooled bikes need air.
Put a house fan in front of the motor when it's running but not moving.

I started one a few weeks ago after laying dormant for maybe 20 years,
3 or 4 minutes it was smoke city.
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Re: 79 CB750K New here

Ba5sKing
well i made this post once and then the computer shut off, so hopefully i can duplicate it well

last year when i started this thread i had quite alot of knowledge gaps to work on. unfortunately i didnt quite believe in 'torque' specs either haha that bit back at me hard, and caused alot of things to come undone while I test rode her and fail under non-designed stresses. particularly the rear brake linkages. so due to college its been a while since i ve had the money or time. but heres rebuild #2!





Pulled Carbs, for anyones info, way easier to take off the four bolts that hold the battery holder in place(so yes you have to take out the battery), pop it down into the frame cavity and pop the rear fender down so you can shift all this back some. air box gets alot more movement this way and i prefer to slip the airboots from the box into the box, best way i have found so far to quickly remove/install those pains in my ass haha



removed air box



New type of handlebars, saw them on another members cb750(his was the f model). such a nice fit, recommended for anyone looking for a sportier position. father helped me install them

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Re: 79 CB750K New here

Ba5sKing
The before manifold + exhaust







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Re: 79 CB750K New here

Ba5sKing
inbetween clean









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Re: 79 CB750K New here

Ba5sKing
after + paint then my favorite, the wrap(fiberglass is itchy!)







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Re: 79 CB750K New here

Ba5sKing




Got a lil artsy with my progress that day
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Re: 79 CB750K New here

Ba5sKing


Can you tell its my first wrap job? Took me a while to figure out where to go from the first pipe. Answer is wrap up to the collector and tye it off the hopefully a metal ziptye provided with the wrap. Fourth header wrap around all tubes before the collector to hide the ziptye's and continue the wrap to the end of the exhaust.









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Re: 79 CB750K New here

Ba5sKing


Had to get a new rear drum plate, due to the spline that the linkage connects to..getting all its teeth sheered round -_- least i could save my fresh pads!!

Next up are some photos of clear coating the frame. This was a tedious process, but I really like the way the spots of the frame that show when the bikes together shine now, plus the whole non rotting effect is nice. I did NOT care to sand it down or remove any current rust. I like the haggard look























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