Topic: One Piece at a Time CB750

[R1gg5]

Hey everyone-

I got a steal of a deal (may include future sarcasm here) on a early 70s CB750 a couple of weeks ago - just $250!

Here's what I know, and I have some questions at the bottom for those of you who are willing to lend some expertise! (start humming Johnny Cash's "One Piece at a Time"… now!)

The frame is a 71'
The engine is a 72'
Looks like forks are 74'
Wiring has 3 fuses, so not sure on the year there.
Seller said engine is rebuilt, but I'm doubting this.
Clutch outer seal apparently leaked and clutch discs went dry. I need to fix the leak and re-wet the plates.
All suspension feels tired or done.
4 into 4s 341 in mostly great shape!

See some photos here: http://www.youtube.com/watch?v=R3dWbqq5UBs (I just posted the video, so you may have to wait for it to be visible)

The dude I bought the bike from said he had three different CB750s, and he paid a guy to produce one solid bike between the three. So what I have is kind of a "frankenbike". He couldn't recall what years he had as donors - but the vin and engine vin clearly indicate there were parts from a 71 and 72. Third donor bike is unknown to me. The seller told me that when he parked it four years ago, it did run and it ran well.

It kicks over. Tank is clear and clean. With some jerry rigging, I can get the starter to engage when you push the "start" button. Fuel lines need to be replaced, not sure on carb condition. Wiring is a mess from first glance, and not sure I'm getting juice at the points- they were left uncovered the past couple of years. I really want to just get a good harness and replace the wiring altogether - if affordable.

What I've done:
• Oil change with new filter and o-rings (now have a very slight leak near the filter)

So my questions:

• Best way to fix a very slight oil leak at the filter?
• My wiring has the three fuse version. Why do I need that? What do those extra two fuses do? With all the various franken-components on the bike, could I more or less treat this like a 71' and go back to a single fuse harness?
• What are the bare essentials for wiring so this will run?

I only want to get this girl to start up and run (or at least attempt), and once that's done, I'm going to strip her down to the frame and start from there. Would love any advice or words of encouragement as I tackle this.

I'm so excited to have this little project to play with! When she's all done, she'll pretty much have the same look and feel, but newer and more shiny!

Oh- parts I'm interested in (in case anyone is willing to sell/part with):
• Proper hand controls for a 71
• Ignition mounting plate for a 71
• Correct 71 headlight bucket
• Not sure about forks - do I need or want 71 forks?
• CORRECT WIRING HARNESS! (or I may build my own)
• Whatever else you recommend I do to get this girl road worthy

I'm not wanting to spend a fortune on this CB, so would love pennywise advice. Thanks all!

[lwahples]

Nice bike, your vid says it's private. Good Luck on your search for the 71 parts.They tend to get pricey.

[R1gg5]

Video should be visible now…

[70CB750]

Welcome! Nice score.

The forks can actually work for you - it is easier to do dual disc on later forks.

Where is the oil filter leak?

[R1gg5]

Where is the oil filter leak?

Dripping straight from where the filter housing cranks on. How tight is tight enough? I cranked it down pretty good. The leak is super slow… is it possible that the o-rings that came with the filter are crap? I put them on properly, wetted with oil, etc. Not sure the best solution on that one.

Thanks for commenting!

[Johnie]

You should only have to snug that oil filter bolt down. It is common on this board where we buy a 750 and end up cutting the filter off because the previous owner cranked it down to much. My hunch is the o-ring around the bolt shaft is bad.

[lucky]

"I cranked it down pretty good." Scares me.  It is not a car.

[Bankerdanny]

More fuses are better than less fuses, so work on fixing the wiring system you have rather than reverting to a 1 fuse system

Not much tightening should be required to seal the oil filter housing. It is possible that 'cranking on it' did more harm than good, it just needs to be snug, not tight.

Since you don't have the original engine there is no particular value to trying to get the whole bike to '71 spec.

[R1gg5]

Just to clarify- I didn't over tighten the oil filter bolt. At first I just put it on snug, very little effort (afraid to break something), but it leaked real good. So then I snugged it up more, but with caution. It's by no measure on too tight- I always err on the side of safety so that I don't cause a more expensive problem.

I supposed that's why I'm asking now- I didn't want to tighten it anymore without input from those who know.

I'll pull it all off this weekend, inspect, and replace the o-rings if need be. Is there a torque setting for this?

and seriously guys - THANK YOU for your input. It's much appreciated as I cut my teeth on this exciting new project.

[Xnavylfr]

The bare minimum wire needed to get it to run, is on the coils(UNDER THE TANK) is a BLACK with WHITE stripe that is Yd so both coils get power from the one wire...
Make a jump wire Yd and connect to both coils and straight to the + post of your battery.   This elimnates ALL other systems from the circuit except ignition..

IF you have GOOD POINTS(gaped correctly), GOOD sparkplugs and good gas flow circuit (CLEAN and SYNCED CARBS) you also have to include TIMING correct, the bike SHOULD start!!!  NO LIGHTS/NO HORN  just engine running!!


Xnavylfr(CHUCK)

[70CB750]

I would check for flateness on the filter housing and the engine. With new o-ring it should not leak.  Used filter housings are quite available if you need replacement.

[Johnie]

Some guys had problems with aftermarket filter o-rings...they were just a bit narrower and leaked as compared to the Honda brand. Not saying all aftermarkets are bad, just some had issues.

[ekpent]

Gas tank is off a 75 or 76 if your wondering about donor years. Think you better be looking for some fresher points by the looks of the rust.Extra fuses in later models were for the headlight and tailight loops.

[phil71]

I think your problem is time management. If you'd have been replacing your points instead of making musical slide shows you might be up and running.  In the pics, what I'm seeing is a wiring harness that's not completely hooked up, or tucked where it should, but I don't see any signs of bastardization . Wiring in the bucket was a rats nest when it was new, and your LH electrical components, while not mounted, all seem to be there and connected.  Get a tetanus shot, and get those barnacled points out of there.

[Johnie]

Just wondering...how does the gas tank interior look? I did like the video...one thing I have noticed on this board is we like pics here. Good job with the music and all...

[R1gg5]

Gas tank interior was super clean. I ran some gas through it and it comes out perfectly clear.

My gas lines at the "T" are junk, so I will pick up some replacement hose soon for that.

----

A friend of mine suggested cranking the engine over with the points just to see if they were sparking or not, so that's why I did what I did with the points. I'll likely change them out. I also have new plugs that I picked up and will replace those soon.


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By the way guys- the video took me all of 2 minutes to pop up on YouTube- even with the music. I figured it was simply the VERY FASTEST way I could present quite a few images in high quality without much trouble. It's more of a slideshow anyway. Adding the song took 10 seconds. It's funny to see the reaction I'm getting over something so simple.

[ekpent]

I liked the video,Johny Cash works for me and the song fit yor project well.

[Johnie]

The next video will be of this bike purrrrrrrrrrrrrrrrrrrrring like a 750 should.

[bjbuchanan]

Don't worry about the video comment. Two finger typers probably think anything like that on a computer takes a while. Check out the link I'm attaching, it can be useful to you possibly with the points

From the looks of it hit the hardware aisle and get some fresh hardware for the points plate

Have fun and enjoy

[R1gg5]

Check out the link I'm attaching, it can be useful to you possibly with the points

Hey bj- looks like you missed the link- please send that if you can find it… and thanks for the comment!

[phil71]

Sorry, that was just a little joke. Admittedly, I hate making videos, and it may take forever, or just feel that way to me.

[bjbuchanan]

Check out the link I'm attaching, it can be useful to you possibly with the points

Hey bj- looks like you missed the link- please send that if you can find it… and thanks for the comment!

http://forums.sohc4.net/index.php?topic=121142.0

That should work

Hey phil,

Depending on time you can whip these videos togther quick, sometimes easier than uploading. My easygoing-ness doesn't translate well to typing, I usually sound like a D!ick really, so I understand

[phil71]

hahahaha, i know what you mean. Middltown's not too far from brooklyn. Let me know if you're stumped. I don't see much there that couldn't be sorted out in a few hours

[bjbuchanan]

I actually live in tarrytown now so I'm much closer. Work and school full time but I would really like to cruise with some other guys with my kinda bike, not just wander around Ttown scaring the locals with my smoker lol

[Raul CB750K1]

Sorry, that was just a little joke. Admittedly, I hate making videos, and it may take forever, or just feel that way to me.

FWIW, I found the joke real funny and not much offensive to the original poster. Just a hint of sarcasm, I found it funny.

[R1gg5]

I've finally found some free time to start working on this bike. I replaced the harness with a good used one- the harness on the bike was taped, soldered, spliced and otherwise hacked quite a bit.

Where I ran into trouble, was the wiring in the headlight bucket. The PO had cut most of the plug receptacles off the parts that plug into the harness, so I still had my work cut out for me to try to match up the wires in the correct manner. I'm going to take a couple of photos and make some notes with questions later today - and hope someone can take a few minutes to correct the problems I've got. At the moment, I only get working head and taillights and NOTHING else. No ignition, turn signals, etc.

I also replaced the points/condensor plate with a new Honda unit, and I set the basics (gaps and general timing). Since I have no spark yet, I can't fine tune the timing right now.

Photos coming, and please, if you can take a moment to point me in the right direction, that'd be so cool. I really want to hear this motor spin up to life!

[lucky]

You do not need a new wiring harness unless you are doing a complete restoration.
All of the wiring harnesses for the CB750 SOHC from 1969-1978 are very similar
except for the left hand control and some minor headlight wiring stuff.

I did a complete restoration using the 1975 Parts & More wiring harness and it was all plug and play except the left hand control.
I think the starter safety switch on the left hand control stuff was a little different.
Easy wiring harness and very simple 3 fuse fuse panel.

[R1gg5]

I had this bike running after rebuilding the carburetors and figuring out enough of the wiring challenges. Unfortunately, when taking her on a test spin around the block, the chain broke and snapped a sizable hole in the gear box, ruining the motor.

After many weeks of trying to locate another engine for the bike, I came across a 75 CB750F basket case with an (apparently) good motor for $250.00. The motor is not an F motor - it's a 76 motor from a K type bike.

Now that I have the F basket case, I wonder if I should build up that bike instead of the 71 K. I don't have the tank or seat pan for the 75 F, but just about everything else is there. The rear disk brake doesn't activate when pressing on the foot pedal - indicating that it's likely that the brakes will need to be fully rebuilt to get them working.

Regardless, my plans for the next step(s) are to strip the bike down completely and get various parts sent off for paint, powder and/or plating. So either frame should be a good candidate.

I won't be doing a natural restoration - neither candidate is ideal for a restoration, so I'm looking to probably build a mostly stock bike with a few modifications with aftermarket parts or parts from other CB750 years. For example, I'm using Norman Hyde "M" bars.

I'd love to get opinions on the frame question and thanks for taking an interest in my project.