Author Topic: Newbie 1972 CB750K owner needs advice--Pics and Video  (Read 3085 times)

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Offline Jamin

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Newbie 1972 CB750K owner needs advice--Pics and Video
« on: May 14, 2009, 08:08:07 PM »
Hello everyone,

I'm a new member here, and excited to have found what seems to be a great community!

A little background on the bike I ended up buying.  This is my first motorcycle.  I test rode a bunch of newer bikes, but after riding a friend's '72 CB450 I knew I wanted a classic Honda.  It just felt like real motorcycling by comparison.  I found some ads on Craigslist and made a list of CB's I wanted to look at.  Armed with a basic understanding of what to look for, I brought a friend along with me to test ride the bike since I only have my permit.  The bike seemed fairly clean and ran okay, so we hopped on and headed out to the main road.  Would you believe we dumped the thing on the first turn!  We were horrified!  The bike lay in a pool of gasoline and oil, and as you can imagine, with heads hung low, we strode the walk of shame all the way back to the owner's house and where I bought the bike.  You break it, you buy it.  To make a long story short, he had admitted to over-filling the oil reservoir earlier (which I know NOW would cause the engine to pump oil out of the overflow which happens to be located by the rear tire).  So when we accelerated through first gear into second, the rear tire was sprayed with oil causing us to lose traction and whip a donut right there in the street.  It was a horrifying experience for both of us and a lesson well-learned.  So anyway, I knew I wanted a CB750, I just didn't think I'd end up buying the second one I tested after dumping it.  An embarrassing day to say the least, but now I need to make the best of it.

I have to admit that I'm not a mechanic, but I'm handy and willing to learn.  I've been reading everything here in the FAQs and have the shop manual, Clymer guide, original owners manual.  I'm trying to get up to speed, but am lacking experience.  This is all new to me. 

The bike had been stored indoors for 6 years under the previous owner.  He said he only put 300 or so miles on the bike during that time.  I realize that storage like this is hard on bikes.  Here are the issues that I know of so far:

- Rear right turn signal cracked (from when we dumped it - replacement part on it's way)
- Right driver's foot peg bent and scraped from when we dumped it, drivable, but I'm going to replace it
- Front brake light switch doesn't work
- Rust in gas tank, found some particles in petcock base and filter, new filter on order
- Cold starter, but runs okay after it's been warmed up
- From about half throttle and open, bike bogs down and loses power.  This seems like a carb jet issue from what I've read here
- Discoloration on exhaust pipes, from what I can piece together (correct me if I'm wrong) this means I'm running hot on those cylinders, probably lean, which could also play into the bog from half throttle on.  Could also be timing that's off and carbs out of sync.
- Jumpy tach and speedo needles (you can see this in the video)
-Throttle is a little tight and sometimes hangs onto revs (again, this might be fixed by a complete tune up and carb sync?)
-Strange scraping/whirring sound from rear wheel.  Don't know if it's chain adjustment or bad wheel bearing.  Chain looks straight and I've adjusted it to factory spec.

I'm posting a video below to show you what I mean. It's a little blurry, but I've moved the camera around to get the mic close to all of the weird little noises it's making.  I'm not sure what these are supposed to sound like, but mine seems a little rattly in the high end, especially from the valve cover area.  Also noted a puttering on the right side exhaust, sort of like a misfire or backfire.  This might be a baffle or something rattling inside?


From what I've read here, the valves probably need adjustment.  Could all of these symptoms be remedied with a good tune up, or do I have bigger problems?  I don't want to continue to ride the bike if I could risk damage.  My goal is for this to be a commuter and cruiser in the summer, and I'll slowly work to restore it over the long winters year after year.  In the short term, unless you all deem it unnecessary, I plan to use this site and my books to do a thorough tune up.  I've ordered a manometer and am going to get a strobe/tach for timing.  I don't have a plug wrench, but am getting one this weekend so will be able to provide some reads from them as well.

Thanks for reading.  I'm very grateful to anyone who might wish to help.

Someone said in an earlier post, that folks around here like pictures.  Here goes:


Side view


Other side


Discoloration on exhaust headers


Broken signal from our foolish oil skating experience


Rear sprocket and exhaust tips, there's a strange whirring sound at the rear tire when coasting with the engine off that may be the chain, or the wheel bearing, I don't know how to tell.  Maybe I'll post a video of it spinning on the center stand.


rear chain, I'll measure and clean and soak when I get to taking everything apart.  For now, loosened some rust with penetrating lube, but teeth and chain look okay to me


swing arm corrosion and rust


carb and choke lever


gauge cluster - bouncy needles on both, but speedo is worse.  why does the speedo needle move when bike is in neutral while revving the engine?


Front wheel and brake-the front brake is squeeky, is this just the way they are, or can this be fixed?  pads look okay and brake lever is a bit wooden.


plug wires and valve cover





VIN on frame indicates this is a 1972K2, previous owner had is listed as a '73


exhaust part number


engine block


rust in gas tank, probably some in float bowl as well, but haven't taken it apart yet.  Petcock fuel filter was damaged, I have a new one on order

« Last Edit: May 16, 2009, 08:08:48 AM by Jamin »
1972 CB750K2

Offline NPHLYT

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #1 on: May 14, 2009, 08:19:33 PM »
Welcome to the addiction.
I wish I could find something that clean! What did you pay for it, if you don't mind me asking? As far as the noise when you spin the back wheel, is sounds like a chain noise, all 3 of my bikes make that noise, and one of them has a new chain.
NPHLYT
1970 CB750 Mutt
1962 Sears Allstate Puch

Offline Industrial Cafe

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #2 on: May 14, 2009, 08:30:49 PM »
OH GOD STOP  ;D the valves are way out, sounds like one is hitting the tappet cover.
 adjust them to spec and then rev it up.
I bought a motor that sounded exactly like that, and it had an impression of the nut and screw in the tappet cover.

other than that looks real good, and welcome to the forum.
everything I say is pure speculation and
I have no idea what I'm talking about  ._.


                                    Marla              .:71CB750:.CAFE

Offline CBJoe

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #3 on: May 14, 2009, 08:36:38 PM »
Welcome to the forum.... more knowledge here than you'll know what to do with (it's just not my knowledge  ;))

I thought that it was a rich fuel situation that caused pipe bluing. 

Have you pulled the plugs?  I'd definitely do that or replace them and then check if you have no idea of the age and mileage on the plugs.  This would be a good indicator on whether you're running lean or rich.

Cheers, Joe
'07 Bonneville Black
'15 Moto Guzzi California 1400
CB750K2 Hot Rod Revival http://forums.sohc4.net/index.php/topic,171693.0.html
'65 CB77
'66 CM91 (C90'ish)

Offline Industrial Cafe

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #4 on: May 14, 2009, 08:37:35 PM »
blue = lean
everything I say is pure speculation and
I have no idea what I'm talking about  ._.


                                    Marla              .:71CB750:.CAFE

Offline wrenchmuch

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #5 on: May 14, 2009, 08:52:33 PM »
Congrats thats a beautiful bike . It looks like you might have some rust in the tank . This can get into the carbs . There are lots of small holes in there that can get plugged up easily . Remove the bowl from the bottom of the fuel petcock to check for debris . Pull one of the float bowls and see if there is junk in there . If there is you have to find the source and clean it up . If you find junk in the carb bowls clean the carbs . Lots of info on carbs in the FAQ or using the search function at the top right of the SOHC/4 Bikes main page . You might also pull the oil pan and clean that out as well . Clean the screen on the oil pump while it is off . When you buy a new gasket for the oil pan consider getting a new oil pump screen as well . A little dirt in the carbs can make these bikes run like crap .
Enjoy :)
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Offline wrenchmuch

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #6 on: May 14, 2009, 08:54:24 PM »
I forgot look in the FAQ for a manual and go through a tune up as well.
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Offline jmckinne

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #7 on: May 14, 2009, 09:03:22 PM »
The popping or "puff-puff" noise from the exhaust is usually helped by carb-sync. Do you know when they were last rebuilt?

Midwest Cycle at 43rd and Nicollet has all the stuff you'll need to Kreme you tank if you go that way - and I recommend it.

Your tach and speedo cables probably need a little lube, that will help with the jumping.

Your bike looks great btw.

I'm in Chaska if you need any help or a carb sync tool etc. I live about 1/2 mile from a practice course for the road test too.

Offline Industrial Cafe

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #8 on: May 14, 2009, 09:05:50 PM »
disassemble and really clean the cables, then use locksmith lube on them. it's graphite.
everything I say is pure speculation and
I have no idea what I'm talking about  ._.


                                    Marla              .:71CB750:.CAFE

Offline Jamin

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #9 on: May 15, 2009, 07:59:15 AM »
Thanks everyone for the warm welcome and helpful tips.  I'll keep this post updated as I make progress.  I plan on poking around this weekend a bit.  In the meantime, is it okay to drive with the valve noise until I can get to it, or should I park it?
1972 CB750K2

Offline BeSeeingYou

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #10 on: May 15, 2009, 08:28:43 AM »
There is a thread or two on tank cleaning so check those out.  I would not use a tank liner unless the tank was seriously compromised by corrosion.  They seem to fail as often as they succeed probably due to application error.  They came bare steel from the factory and once clean with proper care you should not have problems for many years.  In a nutshell in order: electrolysis, acid rinse, baking soda rinse, alcohol rinse, fuel. 
     An 18mm plug socket from Sears will work fine with a short extension for the two middle plugs.  Just take care and thread those two in by hand as you can't see and have to rely on feel to get them in.  These engines tend to make a bit of a racket and it can be compounded by clutch rattle, valve adjustment, cam chain adjustment, and carb sync.
    Welcome aboard.  Maybe I will see you around Minneapolis sometime.
« Last Edit: May 15, 2009, 08:39:51 AM by srust58 »

Offline Magpie

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #11 on: May 15, 2009, 08:42:33 AM »
Nice find! Welcome home!
Cheers,
Cliff.

Offline NPHLYT

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #12 on: May 15, 2009, 10:11:32 AM »
In the meantime, is it okay to drive with the valve noise until I can get to it, or should I park it?

You should park it in my garage until I get my 1980 back on the road  ;D
NPHLYT
1970 CB750 Mutt
1962 Sears Allstate Puch

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #13 on: May 15, 2009, 10:14:28 AM »
Thanks everyone for the warm welcome and helpful tips.  I'll keep this post updated as I make progress.  I plan on poking around this weekend a bit.  In the meantime, is it okay to drive with the valve noise until I can get to it, or should I park it?
I'd park it till you can get them adjusted.



everything I say is pure speculation and
I have no idea what I'm talking about  ._.


                                    Marla              .:71CB750:.CAFE

Offline SOHC4 Cafe Racer Fan

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #14 on: May 15, 2009, 12:22:17 PM »
The bike may be titled as a 1973, if it was originally titled in '73 even if it was a K2 manufactured in 1972.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
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Offline Johnie

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #15 on: May 15, 2009, 12:29:37 PM »
Just a real nice looking bike there.  Really too bad about the spill and damage, but that can be fixed easy enough.  I love the look of these stock bikes.  You got a good one there.  Treat it well and it will last forever.  Welcome to the board.  There is more knowledge here about these bike than you will find at NASA...  :o
1970 CB750K0 - Candy Ruby Red
1973 CB750K3 - Candy Bacchus Olive or Sunflake Orange
1970 Chevy Chevelle SS396 - Cortez Silver
1976 GL1000 Sulphur Yellow

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #16 on: May 15, 2009, 12:44:39 PM »
i forgot to mention the exhaust looks normal
everything I say is pure speculation and
I have no idea what I'm talking about  ._.


                                    Marla              .:71CB750:.CAFE

Offline Jamin

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #17 on: June 05, 2009, 03:28:04 PM »
Thanks for the help.  I adjusted the valves, and cleaned and re-gapped the plugs.  Bike is running much better as well after cleaning the rust out of the tank and float bowls and replacing the petcock and fuel lines.  After reading many posts, I think I just have cam chain noise.  Someone posted in another thread about the rubber adjuster pieces wearing out and cam chain noise getting louder with time.  I'm pretty sure that's what I've got going on.  Adjusting the cam chain made no difference, and the valves weren't far out of adjustment.

Here's my next question, the starter grinds and won't turn the motor over.  Is this the starter clutch, or bad starter unit?  The starter solenoid is clicking loud and clear and the battery is fully charged.  I've blew a main fuse last week, and the fuse holder is melted slightly, and the fuse is pretty hot.  I swapped out all my old fuses for brand new ones.  I went through the bike with electric cleaning spray, and sprayed all the connections I could find.  Also, the front brake light switch has been disconnected per the previous owner and I'm not sure why.  I've also fixed the broken tail light with a new wiring harness.  (see video)

« Last Edit: June 05, 2009, 03:32:08 PM by Jamin »
1972 CB750K2

Offline NastyNip

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Re: Newbie 1972 CB750K owner needs advice--Pics and Video
« Reply #18 on: September 27, 2009, 05:10:45 PM »
For educational purposes I'm curious if you ever remedied the issue with the starter?
Cheers!

1974 CB550K
1978 CB550K