Author Topic: stan's 1977 CB750K  (Read 5640 times)

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Offline stan.

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stan's 1977 CB750K
« on: January 26, 2016, 04:43:03 PM »
Found this bike listed on craigslist for $750.  After going back and forth the owner was not willing to go below his price, so I politely declined and let him know to reach out if he had a change of heart.  A couple weeks later he got in touch and said he'd go to 450 and no less.  I countered with $300 which he adamantly refused.  A couple days later he agreed to that price.  Drove down to pick up the bike with a friend in his pickup truck, and returned home with an out of state titled skeleton and many boxes of parts. 

Offline Desert-SOHC

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Re: stan's 1977 CB750K
« Reply #1 on: January 26, 2016, 04:56:29 PM »
cool
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Offline stan.

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Re: stan's 1977 CB750K
« Reply #2 on: January 26, 2016, 04:58:37 PM »
Life was busy around that time so not much happened for many many months.  I've never owned an older bike before, and come from working on diesel mercedes so the whole machine has been quite intimidating.  The bike came to me in pieces and in unknown running condition, so I never got a chance to see how it all went together to begin with!

The fuel tank was heavily rusted inside, so I put together a little reverse electrolysis system to remove as much as possible.  It worked quite well but will probably need to be repeated before using.

The carburetors were extremely varnished, so I ran them through an ultrasonic bath filled with mineral spirits.  After several trips through with the assistance of wire brushes and toothbrushes they ended up reasonably clean.  I cleaned the jets with various gauges of thin kanthal wiring, replaced the gaskets and float valves, replaced the worn and mashed screws with new JIS screws, replaced a bad choke rail with one from a donor set of carburetors, set the float height, and bench synchronized them with my calipers by checking slide position from behind.

the wiring harness appears to have been modified by several different monkeys at several different points for reasons unknown.  The #2/#3 ignition coil has no continuity on the secondary windings and is presumed dead.  The rectifier is also missing in action.  The starter solenoid has been tested and works, the starter has been tested and turns although it is unknown if it is going to be within the parameters necessary to start the bike.  I intend to replace the missing rectifier with a Vishay VS-36MT80 800 volt 35 amp bridge rectifier.  The state of the voltage regulator is currently unknown.

My next task is sourcing a replacement coil.  Once I have that, I can jump the ignition system together enough to see if the engine will start at all before proceeding further.

As I'm not intending to try and return the bike to factory condition I am strongly considering building a simplified wiring harness.


Another issue to sort out is the rear brake.  A previous owner started on a disc conversion but did not finish.  The wheel is ready to go but the swingarm lacks an attachment point for the brace to the caliper.  there is also no attachment point for the master cylinder.  For the moment I believe I will work on getting the engine to start and sorting out whatever gremlinds present themselves.  After that I will attempt to get the wiring sorted out either with the factory harness or a DIY minimal one.  In conjunction with the wiring I will come up with a solution for head/tail/turns.  Once these things are sorted I will revisit my options with the rear brake - lacing the drum hub i have into the existing rim, or completing the disc swap with the existing rear wheel assembly.

Offline cbxr750

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Re: stan's 1977 CB750K
« Reply #3 on: January 27, 2016, 01:38:31 PM »
Looking like more than a box of parts now! $750 is a lot for that basket case. I paid $300 for a running bike, albeit barely.
Follow my CB750 Monoshock Cafe build
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Offline Desert-SOHC

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Re: stan's 1977 CB750K
« Reply #4 on: January 27, 2016, 02:05:17 PM »
Looking like more than a box of parts now! $750 is a lot for that basket case. I paid $300 for a running bike, albeit barely.

That depends where your from.......the more snow you get the cheaper they are, it all has to do with the quality of the parts. Round my parts that about average...something that runs badly and complete is $1500.00 here. If its missing parts the price starts dropping a little. There getting harder and harder to find for good deals, but then all the old stuff is getting that way.
90 F350 Lariat CS S/C Dually
90 S&S 11SC Cabover Camper
97 FLHTP (under construction)
11 Ranger S/C 2wd

Offline stan.

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Re: stan's 1977 CB750K
« Reply #5 on: January 27, 2016, 02:45:15 PM »
Looking like more than a box of parts now! $750 is a lot for that basket case. I paid $300 for a running bike, albeit barely.

yeah $750 was never going to happen, i was happy at $300 as the worst case scenario would be parting it out and getting 300 out of the parts would have been no issue - even came with two pairs of good tires, one of which has never seen pavement (stems still intact on tread).

Offline stan.

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Re: stan's 1977 CB750K
« Reply #6 on: January 27, 2016, 02:54:47 PM »
ordered connectors from OMP last night, replacement ignition coil / spark plug caps / clutch perch (mine was broken) from dime city, and ordering a rectifier from mouser today.  once these components land I should be able to proceed forward with trying to get spark to the engine so I can attempt starting it!

Paid a visit to Charlie's Place up in Glendale today. I was already on the east side to pick up coffee from this really great micro roaster Trystero that runs out of his garage once a week and makes really tasty stuff, but I digress.  I got to scope out a couple of bikes like mine in person that are fully assembled and took reference photos for later.  Charlie's Place has a great reputation and he only works on old Honda bikes, as he has for 20+ years.  I talked to Charlie about my rear brake predicament and he was of the opinion that reverting to the drum rear was the best option for my situation, so I think I will plan on doing that.  I also ordered the rear gas tank rubber as mine is broken.

I guess I'm going to see how much the cost of an already-assembled spoked drum rear wheel will cost compared to having my drum hub laced into my disc wheel.  One thing that may tilt it towards a whole new wheel is if I can recoup some of my money by selling the disc wheel and associated parts.

Offline seanbarney41

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Re: stan's 1977 CB750K
« Reply #7 on: January 27, 2016, 03:55:12 PM »
whole wheel itself should be cheap and plentiful...shipping? not so much
If it works good, it looks good...

Offline SOHC4 Cafe Racer Fan

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Re: stan's 1977 CB750K
« Reply #8 on: January 27, 2016, 04:31:17 PM »
You should be able to get a whole stock drum brake wheel cheap.  If you re-lace your 1975-76 disc brake spoked hub, it will definitely cost more, but offer better rear braking.  You can also lace it to a aluminum wheel (new or off a 1975-77 GL1000).  You can also get the parts together and have Charlie's lace and true the wheel. 

The disc is cool custom touch, but if money is your primary concern, sell the disc hub (you can list on the Forum classifieds) and buy a stock drum wheel.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
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2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
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Offline stan.

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Re: stan's 1977 CB750K
« Reply #9 on: January 27, 2016, 07:09:10 PM »
You should be able to get a whole stock drum brake wheel cheap.  If you re-lace your 1975-76 disc brake spoked hub, it will definitely cost more, but offer better rear braking.  You can also lace it to a aluminum wheel (new or off a 1975-77 GL1000).  You can also get the parts together and have Charlie's lace and true the wheel. 

The disc is cool custom touch, but if money is your primary concern, sell the disc hub (you can list on the Forum classifieds) and buy a stock drum wheel.

at this point i'm 100% going rear drum, the debate is lacing the spare drum hub i have into the wheel i have (~$200 between new spoke set and labor) or finding someone else's complete spoked drum wheel to buy.  If I buy a whole drum wheel from someone then I am thinking that selling my complete disc wheel setup (wheel, rods and things, master cylinder and stuff, pedal, etc) could recoup some of the cost of the purchased drum wheel.

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #10 on: January 27, 2016, 07:52:13 PM »
Nice project,subscribed
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline Stev-o

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Re: stan's 1977 CB750K
« Reply #11 on: January 27, 2016, 08:26:50 PM »
Good progress!   You sure you need a coil?  Very rare do they go bad. 

Do you have the rear caliper? Those are hard to find. 
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline stan.

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Re: stan's 1977 CB750K
« Reply #12 on: January 28, 2016, 03:01:00 PM »
Good progress!   You sure you need a coil?  Very rare do they go bad. 

Do you have the rear caliper? Those are hard to find.

diagnostics method i found was to check resistance on both primary and secondary windings to verify they are within spec.  lack of continuity indicating a faulty coil, which was the case with one of them even after i clipped the wires shorter to make sure i was getting a good fresh connection.

yes i have the rear caliper.

Offline stan.

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Re: stan's 1977 CB750K
« Reply #13 on: January 29, 2016, 04:26:10 PM »
parts from dime city arrived today!  clutch perch installed and working, but the clutch is still not disengaging.  could the lack of oil in the system right now make the clutch not disengage?  I've opened the clutch cover and confirmed it is actuating fully as expected, but I feel that it may be noteworth that the bike is currently not filled with oil, oil filter and housing are off, and oil tank is off. 

replacement ignition coil needed a little coaxing to fit onto the stock bracket but is all together now and I believe ignition system is all good now.

i guess my next step is to reinstall the rebuilt carburetors, make a little fuel bottle to hook up to them, and attempt starting the bike.

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #14 on: January 29, 2016, 04:30:26 PM »
parts from dime city arrived today!  clutch perch installed and working, but the clutch is still not disengaging.  could the lack of oil in the system right now make the clutch not disengage?  I've opened the clutch cover and confirmed it is actuating fully as expected, but I feel that it may be noteworth that the bike is currently not filled with oil, oil filter and housing are off, and oil tank is off. 

replacement ignition coil needed a little coaxing to fit onto the stock bracket but is all together now and I believe ignition system is all good now.

i guess my next step is to reinstall the rebuilt carburetors, make a little fuel bottle to hook up to them, and attempt starting the bike.

A good way to install the clutch plates is to soak the fiber plates in engine oil for a while and then assemble the complete clutch 'pack'/plates w/ oil on them and it should disengage much better;great progress  :)
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline stan.

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Re: stan's 1977 CB750K
« Reply #15 on: January 29, 2016, 04:34:05 PM »
the clutch is still not disengaging.  could the lack of oil in the system right now make the clutch not disengage?  I've opened the clutch cover and confirmed it is actuating fully as expected, but I feel that it may be noteworthy that the bike is currently not filled with oil, oil filter and housing are off, and oil tank is off. 


A good way to install the clutch plates is to soak the fiber plates in engine oil for a while and then assemble the complete clutch 'pack'/plates w/ oil on them and it should disengage much better;great progress  :)

i had no plans to be mucking around with the clutch plates as it'd require buying / crafting a tool to get that one nut off and absent some diagnosed issue i'd just rather not.  see attached photo for how much the arm under the clutch cover is moved when the hand control is actuated.

is it safe to presume that it may get the oil it needs once the system is closed up and filled up?  for the testing i need to do next it's ok if the clutch wont disengage yet as i'm still able to put the bike in neutral.  maybe once the engine is running the system pressure will be adequate to lubricate the clutch plates?

Offline stan.

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Re: stan's 1977 CB750K
« Reply #16 on: January 29, 2016, 04:35:15 PM »
in case anyone is curious of how the oem replacement type coils from dime city fit the stock bracket and compare to the stock coils, here's a photo of mine with both a stock coil and a replacement coil on the bracket.

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #17 on: January 29, 2016, 04:37:47 PM »
I'd take the plates out(impact on the clutch hub nut)and inspect them(they may have rust on the steel clutch plates..)and then clean and oil them if all looks good;better to remove them to know for sure.
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline stan.

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Re: stan's 1977 CB750K
« Reply #18 on: January 29, 2016, 04:55:27 PM »
after some more coaxing, i can spin the wheel by hand with the hand control actuated and the transmission in gear.  it's draggy but maybe that's ok enough for now given the current lack of oil?

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #19 on: January 29, 2016, 05:05:14 PM »
I would disassemble the clutch pack if it was me,that way you can see the clutch plates and know their cond. The engine is dry sump so it may be a bit of running before they get totally saturated w/ enough oil to have smooth clutch action.. that can be hard on your trans. if the clutch is not releasing good because of rusty clutch steel plates.
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline Stev-o

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Re: stan's 1977 CB750K
« Reply #20 on: January 29, 2016, 05:28:25 PM »
If you can spin the wheel, you may be ok.

After coil install, did you check spark at the plugs?
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline stan.

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Re: stan's 1977 CB750K
« Reply #21 on: January 29, 2016, 05:41:08 PM »
If you can spin the wheel, you may be ok.

After coil install, did you check spark at the plugs?

not yet, i'm going to be wiring up a very minimal harness to try and start the engine for the first time. 

would this be a valid test of the ignition system:
-12v jumped direct to coils
- ground to chassis
-coils connected to points
-jumper cable clamped onto body of spark plug / plug wire plugged into plug
-spin engine with kick starter, observe plug for spark

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #22 on: January 29, 2016, 05:45:38 PM »
Make sure the spark plug steel bodies are grounded to the engine/frame when you inspect the center electrode for spark.
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline stan.

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Re: stan's 1977 CB750K
« Reply #23 on: January 29, 2016, 05:50:34 PM »
Make sure the spark plug steel bodies are grounded to the engine/frame when you inspect the center electrode for spark.

used a car jumper cable to ground engine to battery, and spark plug to engine.

turned the engine over with the kick starter, we've got sparks!!!!
« Last Edit: January 29, 2016, 05:58:58 PM by stan. »

Offline grcamna2

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Re: stan's 1977 CB750K
« Reply #24 on: January 29, 2016, 06:17:36 PM »
the coils are good now?  :)
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.