Author Topic: 1972 CB750K2, 33 years off the road  (Read 7232 times)

0 Members and 2 Guests are viewing this topic.

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
1972 CB750K2, 33 years off the road
« on: February 22, 2022, 08:30:46 AM »
I just purchased a 1972 CB750K2 that was last on the road 33 years ago. It was a west coast bike and has been stored in a garage so the rust is minimal. It "ran when parked" and has most of the OEM parts present except for a few bolt on customs and those fugly flames.

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #1 on: February 22, 2022, 08:33:14 AM »
The first job after getting it home was to get the fairing, case protector and luggage rack off so I could see what I had.

The finned clutch, points, mag and tappet covers are obviously not stock. I will replace those with OEM parts. I think I will remove the oil pressure gauge as well.
« Last Edit: February 22, 2022, 08:36:16 AM by Delsolid »

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #2 on: February 22, 2022, 08:39:45 AM »
The gas tank is both great and terrible at the same time. Internally there is almost no rust. Definitely not what I was expecting. I will still clean it out but it is a very good sign. There appears to be no dents at all. However, the flame paint job is abysmal and I think a 10 year old could do better. It will definitely get a complete repaint.

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #3 on: February 22, 2022, 08:44:44 AM »
The OEM gauges and controls are all still here. The rhino horn triple clamp and the K2 only turn signal cancel is still here so it looks like nobody tore much apart. The throttle is stuck and the brake MC is dry. Lots of work required in those areas.

The key has been moved up to the handlebar area but I will move it back to the OEM location I think. The grips look like a beaver chewed on them.

Offline Stev-o

  • Ain't no
  • Really Old Timer ...
  • *******
  • Posts: 34,281
  • Central Texas
Re: 1972 CB750K2, 33 years off the road
« Reply #4 on: February 22, 2022, 10:19:58 AM »
Great find, congrats.   The "throttle stuck" issues are most likely the slides within the carbs, pull the rack and use spray lube to try to release them.   Carbs will need a rebuild too, dont buy the cheap rebuild kits you see online, instead use all the original brass if intact. 

Great project, good luck!
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #5 on: February 22, 2022, 11:31:23 AM »
Carbs will need a rebuild too, dont buy the cheap rebuild kits you see online, instead use all the original brass if intact.

Definitely using the original brass if at all possible. What would you define as a good kit rebuild vs a cheap kit? really, I would assume I'm just going to use the gaskets/seals/o-rings and nothing else unless necessary. Who is a trustworthy vendor that stocks a lot for these bikes and tries to only carry good quality maintenance type stuff (filters, cables, ignition, carb kits, petcock kits etc...)?

I'm essentially new to these kinds of bikes, last M/C I owned was 25+ years ago and it was a 2-stroke dirt bike. I have never owned a street legal bike, let alone a 500lb beast.
« Last Edit: February 22, 2022, 11:33:44 AM by Delsolid »

Online Phoenix

  • Hot Shot
  • ***
  • Posts: 272
  • 4 wheels move the body. 2 wheels move the soul
Re: 1972 CB750K2, 33 years off the road
« Reply #6 on: February 22, 2022, 11:58:01 AM »
Looks like a good, strong patient.  Make sure to get a copy of Hondaman's book.  Read it as you get into each sub-section of the bike.  I made a couple of mistakes by not taking the time to re-read it as I did it.  Good luck and use offical Honda parts anywhere you can.  Ask plenty of questions on the site.  These guys have all the answers.
Ed Spengeman
Indy
1971 CB750K1 (Stock)
1973 CB350 Twin  (Gone)

Offline rickmoore24

  • Be led by your dreams, not pushed by your problems.
  • Hot Shot
  • ***
  • Posts: 747
  • I <3 SOHC4's
    • Rosenbard Films
Re: 1972 CB750K2, 33 years off the road
« Reply #7 on: February 22, 2022, 01:58:03 PM »
Nice find! I like them like that, I'll bet it would run pretty easily if the carbs are anything like the inside of the tank. Lube up the carbs and throttle mechanisms, clean out the jets and it'll likely come to life. Making sure it has oil in it and a good battery of course.  ;D  Good luck with it! Rick.
1972 CB750 K2 (Daily Runner)
1972 CB750 K2 (Sold)
1973 CB750 K3 (Hardtail 836cc)
1998 CBR F3 - R.I.P., went down on the 101 in Calabasas, Ca.
1995 EG6

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #8 on: February 22, 2022, 02:20:50 PM »
I didn't get any keys with it but they should be here within the week. Cant do anything till then because I cant raise the seat to replace the battery!

Online seanbarney41

  • not really that much younger than an
  • Really Old Timer ...
  • *******
  • Posts: 10,811
Re: 1972 CB750K2, 33 years off the road
« Reply #9 on: February 22, 2022, 04:04:01 PM »
bah!..unbolt the seat latch/lock
If it works good, it looks good...

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,810
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: 1972 CB750K2, 33 years off the road
« Reply #10 on: February 22, 2022, 06:23:35 PM »
Carbs will need a rebuild too, dont buy the cheap rebuild kits you see online, instead use all the original brass if intact.

Definitely using the original brass if at all possible. What would you define as a good kit rebuild vs a cheap kit? really, I would assume I'm just going to use the gaskets/seals/o-rings and nothing else unless necessary. Who is a trustworthy vendor that stocks a lot for these bikes and tries to only carry good quality maintenance type stuff (filters, cables, ignition, carb kits, petcock kits etc...)?

I'm essentially new to these kinds of bikes, last M/C I owned was 25+ years ago and it was a 2-stroke dirt bike. I have never owned a street legal bike, let alone a 500lb beast.

That looks just like mine! :D
Go to PartsNmore.com for the carb refurbishing parts.
The rebuild kits I use are the O-ring kit #48-0791, the float bowl gasket #20-8035, and the float valve (if your old ones are not sealing anymore) #48-5009. These float valves have stiffer springs than the OEM ones, so set the floats to 25mm instead of 26mm to make the running levels come out the same.

If the velocity stcks between the airbox and the carbs are shrunk and won't seal in the airbox, use their #48-0759 boot to fix them up.
The intake air hoses might be really stiff and hard: if so, they will likely leak vacuum also when you put them back on. You can use the Oetiker clamps #09-050 (50mm) to close harder, just be careful to not cut thru the hoses then, as these are aircraft-quality and WILL let you overtighten them, easily, cutting right into the hoses!

The grease in the spark advancer cam is probably dried out and stiff, which will make the spark advancer wonky and sticky. Remove the 6mm nut and the big one on the end of the crankshaft by the points, and spray a little WD40 into the points cam there to start loosening it back up, then put those nuts back on. This will not alter the spark timing it last had.

A suggestion for the keyswitch: we moved many of then back on the frame to be just in front of the choke lever from the carbs, under the tank. This stopped them from getting wet in the rain, making them last far longer. You'll need the Honda keyswitch bracket, like was used in the original position, to move it - and the wires are long enough.

If you run into battery charging troubles (low charge), remove the voltage regulator's cover (carefully - don't break the rubber gasket if you can) and run some 2000 grit emery paper thru the contacts on the regulator. This will remove the silver oxide that grew from non-use and will make it work right again.

If you haven't put fuel in the tank yet: remove the fuel petcock's cover plate (2 tiny screws) and dab a bit of oil or grease onto the surface of the rubber seal inside. This will restore it once it gets wetted with gas again.

Does it still have the turn-signal beeper? I still use mine, although it sounds like it has a 'voice crack' 2-tone pitch to it now. :D
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline BenelliSEI

  • Really Old Timer ...
  • *******
  • Posts: 9,875
  • 1969 cb750
Re: 1972 CB750K2, 33 years off the road
« Reply #11 on: February 22, 2022, 06:29:52 PM »
Great find, congrats.   The "throttle stuck" issues are most likely the slides within the carbs, pull the rack and use spray lube to try to release them.   Carbs will need a rebuild too, dont buy the cheap rebuild kits you see online, instead use all the original brass if intact. 

Great project, good luck!

Great find, great project.!

I had a pair of slides that just would not move. After tearing down the carbs as far as I could, put them in a pot of boiling water for 5-10 minutes. Just slid right out.

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #12 on: February 23, 2022, 02:26:08 PM »
That looks just like mine! :D
Go to PartsNmore.com for the carb refurbishing parts.
The rebuild kits I use are the O-ring kit #48-0791, the float bowl gasket #20-8035, and the float valve (if your old ones are not sealing anymore) #48-5009. These float valves have stiffer springs than the OEM ones, so set the floats to 25mm instead of 26mm to make the running levels come out the same.

If the velocity stcks between the airbox and the carbs are shrunk and won't seal in the airbox, use their #48-0759 boot to fix them up.
The intake air hoses might be really stiff and hard: if so, they will likely leak vacuum also when you put them back on. You can use the Oetiker clamps #09-050 (50mm) to close harder, just be careful to not cut thru the hoses then, as these are aircraft-quality and WILL let you overtighten them, easily, cutting right into the hoses!

The grease in the spark advancer cam is probably dried out and stiff, which will make the spark advancer wonky and sticky. Remove the 6mm nut and the big one on the end of the crankshaft by the points, and spray a little WD40 into the points cam there to start loosening it back up, then put those nuts back on. This will not alter the spark timing it last had.

A suggestion for the keyswitch: we moved many of then back on the frame to be just in front of the choke lever from the carbs, under the tank. This stopped them from getting wet in the rain, making them last far longer. You'll need the Honda keyswitch bracket, like was used in the original position, to move it - and the wires are long enough.

If you run into battery charging troubles (low charge), remove the voltage regulator's cover (carefully - don't break the rubber gasket if you can) and run some 2000 grit emery paper thru the contacts on the regulator. This will remove the silver oxide that grew from non-use and will make it work right again.

If you haven't put fuel in the tank yet: remove the fuel petcock's cover plate (2 tiny screws) and dab a bit of oil or grease onto the surface of the rubber seal inside. This will restore it once it gets wetted with gas again.

Does it still have the turn-signal beeper? I still use mine, although it sounds like it has a 'voice crack' 2-tone pitch to it now. :D

Thanks for the lead. PartsNmore looks like they have a huge selection. My wallet is going to take a hit.

I plan on removing the tank, petcock, carbs etc... completely and clean it all out before I try anything. Same on the ignition side. Better to just do the groundwork now rather than just dive and and try to start it. I think there will also be a lot of rubber than needs replacing before I get into anything too deeply.

The beeper is there but I haven't powered up the bike yet to see if it cheeps, beeps, creaks or wheezes.

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,810
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: 1972 CB750K2, 33 years off the road
« Reply #13 on: February 23, 2022, 04:56:15 PM »
That looks just like mine! :D
Go to PartsNmore.com for the carb refurbishing parts.
The rebuild kits I use are the O-ring kit #48-0791, the float bowl gasket #20-8035, and the float valve (if your old ones are not sealing anymore) #48-5009. These float valves have stiffer springs than the OEM ones, so set the floats to 25mm instead of 26mm to make the running levels come out the same.

If the velocity stcks between the airbox and the carbs are shrunk and won't seal in the airbox, use their #48-0759 boot to fix them up.
The intake air hoses might be really stiff and hard: if so, they will likely leak vacuum also when you put them back on. You can use the Oetiker clamps #09-050 (50mm) to close harder, just be careful to not cut thru the hoses then, as these are aircraft-quality and WILL let you overtighten them, easily, cutting right into the hoses!

The grease in the spark advancer cam is probably dried out and stiff, which will make the spark advancer wonky and sticky. Remove the 6mm nut and the big one on the end of the crankshaft by the points, and spray a little WD40 into the points cam there to start loosening it back up, then put those nuts back on. This will not alter the spark timing it last had.

A suggestion for the keyswitch: we moved many of then back on the frame to be just in front of the choke lever from the carbs, under the tank. This stopped them from getting wet in the rain, making them last far longer. You'll need the Honda keyswitch bracket, like was used in the original position, to move it - and the wires are long enough.

If you run into battery charging troubles (low charge), remove the voltage regulator's cover (carefully - don't break the rubber gasket if you can) and run some 2000 grit emery paper thru the contacts on the regulator. This will remove the silver oxide that grew from non-use and will make it work right again.

If you haven't put fuel in the tank yet: remove the fuel petcock's cover plate (2 tiny screws) and dab a bit of oil or grease onto the surface of the rubber seal inside. This will restore it once it gets wetted with gas again.

Does it still have the turn-signal beeper? I still use mine, although it sounds like it has a 'voice crack' 2-tone pitch to it now. :D

Thanks for the lead. PartsNmore looks like they have a huge selection. My wallet is going to take a hit.

I plan on removing the tank, petcock, carbs etc... completely and clean it all out before I try anything. Same on the ignition side. Better to just do the groundwork now rather than just dive and and try to start it. I think there will also be a lot of rubber than needs replacing before I get into anything too deeply.

The beeper is there but I haven't powered up the bike yet to see if it cheeps, beeps, creaks or wheezes.

Something to watch out for: the keyswitches that are aftermarket type are not heavy-duty enough (12-13 amps needed) for this bike. Most of them are made in China for EMGO and marketed with or without the name, and they are clones of the one for the CB350 bikes (8 amps). When in use, these will melt the Black wire right off the back of the switch when you turn on the turn signal for a lane-change move on the freeway (guess how i know that? And not just once...). If you can't get the genuine honda version, I have a relay kit that you can install that will allow you to use the lesser switch without problems.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #14 on: February 23, 2022, 06:22:32 PM »
Hopefully the OEM switch will still be ok. I have a set of the proper keys coming in the next few days and then I will know for sure. I'm going to stick with the original parts whenever possible.

Offline rickmoore24

  • Be led by your dreams, not pushed by your problems.
  • Hot Shot
  • ***
  • Posts: 747
  • I <3 SOHC4's
    • Rosenbard Films
Re: 1972 CB750K2, 33 years off the road
« Reply #15 on: February 24, 2022, 07:50:24 AM »
OEM will be best. Had an EMGO switch that failed me once and I'll never use them again, pulled out the original (with keys) from the parts bin and there have been no issues since the rebuild in 2010.   ;)
1972 CB750 K2 (Daily Runner)
1972 CB750 K2 (Sold)
1973 CB750 K3 (Hardtail 836cc)
1998 CBR F3 - R.I.P., went down on the 101 in Calabasas, Ca.
1995 EG6

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #16 on: February 24, 2022, 08:48:06 AM »
OEM will be best. Had an EMGO switch that failed me once and I'll never use them again, pulled out the original (with keys) from the parts bin and there have been no issues since the rebuild in 2010.   ;)

Yeah, I have been working as a design engineer in the automotive aftermarket for the last 20 years and before that I worked as an engineer at Honda for 6 years.

Just because something is new and shiny and looks like the OEM part doesn't necessarily mean it is anywhere near as good as the OEM part. The amount of engineering that goes into the OEM parts, both in design, mfg and quality control is staggering. A lot of reproduction parts just try to look the same but inside are just cheap. There are definitely some very good aftermarket and reproduction parts, you just cant assume that all of them are.

Offline andy750

  • Really Old Timer ...
  • *******
  • Posts: 7,938
Re: 1972 CB750K2, 33 years off the road
« Reply #17 on: February 24, 2022, 06:41:18 PM »
Great project and following along as a fellow K2 owner. Love your seat!!!
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #18 on: February 25, 2022, 09:03:56 AM »
OEM will be best. Had an EMGO switch that failed me once and I'll never use them again, pulled out the original (with keys) from the parts bin and there have been no issues since the rebuild in 2010.   ;)

The replacement keys that I got off of ebay using the number on the lock face arrived yesterday and after a bit of graphite lube on the housing it works like a charm! It was stiff and clunky at first but after a ton of cycles and more dry lube the key feel is solid and reassuring! Don't know if it works electrically but it sure gives a satisfying click!

Got the seat raised and pulled the very dead battery out for replacement. The positive battery lead is corroded away to nothing. More parts on order.

Under the seat there is a document compartment and it still had the owners manual in it! Well used but original. There was also 3 registration cards, 1978, 1980 and 1982. These were in the name of the guy whose estate I got the bike from. There was also a business card in the pack with a note stating that if the bike was stolen or lost he would pay a reward for it's return. This was dated 1975 and the card was the same guy. This may have really been a 1 owner bike. His daughter (my sister in law) who I dealt with said she thought he bought it new and also bought a matching one for his wife but couldn't say for 100% sure since she was probably like 5 in 1972.
« Last Edit: February 25, 2022, 11:14:45 AM by Delsolid »

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #19 on: February 25, 2022, 11:32:56 AM »
The "throttle stuck" issues are most likely the slides within the carbs, pull the rack and use spray lube to try to release them.
I had a pair of slides that just would not move. After tearing down the carbs as far as I could, put them in a pot of boiling water for 5-10 minutes. Just slid right out.

I got the tank and airbox off. The slides look very clean and working the throttle didn't do anything at the carbs but moving the mechanism on the carbs did allow it to move a bit. I removed the cables the the carbs opened and closed but were a bit stiff. The throttle was still stuck. Played with the cables themselves and they turned out to be the issue. I think water got in one of them and it's all loaded up with internal corrosion or gunk. I'll replace both the push/pull cables and clean out the twist throttle mechanism.

Got the carbs off. The rubber boots between the head and carbs are as hard as concrete. There is no way to expect them to seal so new ones (and clamps) are now on order. The inside of the throttle bores look very clean. I haven't opened up a float bowl yet and I expect those to be a mess.

The intake ports and valve pockets look clean.

Next up - the carbs!

Offline Stev-o

  • Ain't no
  • Really Old Timer ...
  • *******
  • Posts: 34,281
  • Central Texas
Re: 1972 CB750K2, 33 years off the road
« Reply #20 on: February 25, 2022, 12:57:00 PM »
Always nice to find the owners manual and the note is a bonus!  Did you get a title? If he was the origianl owner, the title would be from '72 or '73. 
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline MauiK3

  • A K3 is saved
  • Old Timer
  • ******
  • Posts: 4,267
  • Old guy
Re: 1972 CB750K2, 33 years off the road
« Reply #21 on: February 25, 2022, 01:16:32 PM »
Yes, very cool with the note.
Looking forward to the progress.
1973 CB 750 K3
10/72 build Z1 Kawasaki

Offline Delsolid

  • Full Member
  • *
  • Posts: 56
Re: 1972 CB750K2, 33 years off the road
« Reply #22 on: February 25, 2022, 01:45:44 PM »
Always nice to find the owners manual and the note is a bonus!  Did you get a title? If he was the origianl owner, the title would be from '72 or '73.

Since the whole thing is an out of state probate & extended family thing it is a little more convoluted than I would wish. But the title is supposed to exist and will be forwarded when it is cleared through probate. For now it is just a bill of sale transaction.

Offline Ssicbx

  • Full Member
  • *
  • Posts: 18
Re: 1972 CB750K2, 33 years off the road
« Reply #23 on: February 25, 2022, 03:56:32 PM »
Nice find, I can't believe people still find these things unmolested.  Anyway I'm in the process of finishing my K4, this bike was built from three bikes.  I had a K2 in the 70's and it had a luggage rack like yours.  So if you want to part with it I would be interested. 
Getting ready to pull the trigger on the remaining parts/tires.   
Good luck on the rebuild. 

Offline rickmoore24

  • Be led by your dreams, not pushed by your problems.
  • Hot Shot
  • ***
  • Posts: 747
  • I <3 SOHC4's
    • Rosenbard Films
Re: 1972 CB750K2, 33 years off the road
« Reply #24 on: February 28, 2022, 06:58:05 AM »
The manual and note are awesome! Now if you can track down his wife's CB, you'd really be cooking.  ;D
1972 CB750 K2 (Daily Runner)
1972 CB750 K2 (Sold)
1973 CB750 K3 (Hardtail 836cc)
1998 CBR F3 - R.I.P., went down on the 101 in Calabasas, Ca.
1995 EG6