Author Topic: Get 1972 CB750K2 Ready to Ride  (Read 142 times)

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Offline sacto929

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Get 1972 CB750K2 Ready to Ride
« on: October 26, 2020, 07:35:42 am »
Hello SOHC4 brain trust, I seek your guidance and insight on my next project.

When my Dad passed in 2017, I inherited his CB750K2 (5/1972 mfg date) in metallic orange with 5895 original miles.  It was last registered in 1987, but likely last moved under its own power several years before that.  I can remember riding with Dad to pre-K and/or kindergarten, so that would be in the 1979-1980 timeframe, and I'm not sure if he rode it much after that. 

When I pulled it out of the shed in Northern CA as I moved to AL in 2017, the bike was dusty, spider webbed (actual spiders, not cracks in the paint), and had some very light spots of surface rust on the chromed parts.  Since moving to AL, it has been in my garage patiently awaiting its turn, and while I have rinsed the dust off, the surface rust has increased a little bit.  The gas tank appears rusty inside, the oil tank appears pretty dry (I haven't looked with a flashlight), and the front brake reservoir is dry.  When I moved it, I was able to air the times up and roll it without issue.  I was really surprised that after 40 years the tubes held air for months before slowly leaking down.

So finally, to my questions.  Where should I start to get this bike ready to ride again?  I'm not interested in mods at this point, unless absolutely necessary, or where we've gotten smarter in the meantime.  I will be looking at an AGM or LiFePO4 battery, for example.

There is an amazing amount of detail on the forum and within Hondaman's book (which I bought and read) regarding specific tear down and rebuild areas, but I'm seemingly missing the first part of the decision tree, which is what I should be looking for before tearing anything down. 

I'm assuming that I'll need to refresh most of the rubber bits.  I know I'll need a new throttle cable due to rust at the handle.  The front brake system needs to be refreshed / rebuilt.  Tires and tubes will need to be replaced, etc.

I'll get some pics up when I have a moment to take some, or if there are requests to see certain areas.

Thanks in advance for all your help!

1972 CB750K2, 2000 R1150GS, 2006 CRF250X

Offline MauiK3

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Re: Get 1972 CB750K2 Ready to Ride
« Reply #1 on: October 26, 2020, 09:02:32 am »
Nice to hear another survivor will get saved!

Here are just a few of the many things you need to look at. You already mentioned brakes which will be needing help. Hondaman's book can guide you through all of this.

1. Carbs, they will need a careful going through.
2. Get the tank and pet cock cleaned up.
3. Change the oil
4. Carefully turn the engine over after assuring there is oil in it
5. Thorough tune up
6. See if it will run
7. Hold off on a lithium battery, it can be dangerous, much information here, stick with AGM
8. If you get it running, put around on it for a bit to see what else needs attention
9. Don't use anything "scratchy" on the chrome
10. The tires are too old to be safe, be careful

You likely will need to do all the seals and such in the engine, they are all old and stiff, get ready for a fun and rewarding journey and keep the forum up to date, there is lots of help here. Others will chime in I'm sure
1973 CB 750 K3
2009 Ruckus!

Offline Phoenix

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Re: Get 1972 CB750K2 Ready to Ride
« Reply #2 on: October 26, 2020, 10:55:45 am »
Welcome aboard.  Misery loves company.  Kidding.  I was in the same situation after taking my bike out of my shed after 26 years.  Mark's book wasn't printed yet but I took full advantage of the site.  I still had a Chiltons manual and downloaded a shop manual from this site.  I gave her a good wash job and started on each system.  Rebuilt the master cylnder and caliper.  Replaced the pucks.  No big deal.  Took rear brake apart.  Put in new shoes.  Replace the air filter and see if any birds were living in there.  Took the clutch plates out and checked to see if they were free.  Adjusted clutch.  Replaced and gapped plugs.  Changed oil and filter.  Make sure old oil doesn't have sparkly stuff in it.  Replace battery with AGM.  Drain and refill forks with ATF.  If they don't leak, ok for now,Each day you work on it try the kick starter to confirm it is still free.  When you replace the cables don't go cheap, they won't last.  Try to go with Honda parts and avoid problems.  AS far as starting,  squirt some oil on the rockers thru the ports and spin the engine over a few times with the kill switch off.  If it runs, do a 3000 mile tuneup and, hopefully, you can work on it in a more leisurely manner.  Remember, Marks book is the Bible.  Each time you work on a system, read about it in the book.  Trust me, EACH TIME.  If you have questions, ask here.  These guys have all the answers.  Good luck.
Ed Spengeman
1971 CB750K1 (Stock)
1973 CB350 Twin  (Gone)

Offline BenelliSEI

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Re: Get 1972 CB750K2 Ready to Ride
« Reply #3 on: October 26, 2020, 11:36:14 am »
I agree 100% with all of the above. Generally, with a project like yours, I like to do as little as possible to get the bike running. It’s sometimes surprising how little it takes, especially with a bike that has been stored properly......
1. Take the fuel tank off and put it to one side. It will need work.
2. Unclip and remove the 4 float bowls. Removing the entire air filter makes this easier. Are they full of dry crud, or relatively clean? Get them really clean.
3. Carefully remove the float pins, floats and needle valves. Lay them out somewhere in the order removed. Be VERY careful removing the float pins. Don’t hit them with anything. The posts will snap off the carb body! Soak them in solvent and use a very small pin to push them out. Back and forth, use very little force.
4. Remove the idle jets (small) and main jets (large). Soak them in carb cleaner and blow them clean with air. Don’t be tempted to push anything through them. They will get damaged. Soak and blow until you can see through all the holes.
5.carefully put everything back the way you found it.
6. Hook up a temporary fuel tank. Lots of places sell remote fuel tanks or you can use one from a small lawn mower. Be creative; I used a very large  turkey baster (remove the bulb) for years.
7. Drain the old oil from the tank and engine. Fill with cheap 10/40 oil.
8. I like to install an oil pressure gauge on the main gallery (in the plug at the right end, past the oil pressure switch). If your oil pressure light works, you can chance trusting it.
9. Clean the points and give it a whirl.....
« Last Edit: October 26, 2020, 11:47:15 am by BenelliSEI »

Offline seanbarney41

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Re: Get 1972 CB750K2 Ready to Ride
« Reply #4 on: October 26, 2020, 05:04:24 pm »
Yup...here is how I have gone about this several times.
 1. Get the engine running.  Often, oil burning, oil leaks, low compression will improve considerably after 100 miles or so of riding.  Other times not, so this how I assess if the engine needs to come out of the frame.
  2.  Make the bike safe to ride...brakes, chain, tires, cables.
  3.  Through riding, you can assess what else needs improvement.  If you realize this is not a modern superbike and are happy to allow it to be its 40+ year old self, you will be pleasantly surprised to see that the knowledge and parts to get much closer to modern superbike performance are available.
  4.  Make it look nice.
If it works good, it looks good...

Offline sacto929

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Re: Get 1972 CB750K2 Ready to Ride
« Reply #5 on: October 26, 2020, 06:31:32 pm »

Thank you so much for your reasoned and pragmatic experiences.  That is exactly the information I was looking for.

I'm definitely not expecting the K2 to perform like a modern sport bike.  I actually started my riding career on sport bikes, then to large dual sports, then to dirt bikes.  I seem to do things backwards....  ;D  Brakes are the greatest improvement, in my opinion, so I know I'm going backwards again there.

I will definitely keep track of the journey!
1972 CB750K2, 2000 R1150GS, 2006 CRF250X