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Author Topic: '73 CB750 - New project and first CB - what 4-1 is this?  (Read 1726 times)

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Offline enriquez

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'73 CB750 - New project and first CB - what 4-1 is this?
« on: December 18, 2011, 05:15:28 PM »
Hey there,

I'm new to the forum and a happy new CB750 owner.  Picked up this '73 today, everything has to be gone through.  Engine is seized but the bike came with a second engine in good shape.  I'm sure I'll have plenty of questions along the way and look forward to posting the progress.  My plan is to get it running in stock form first, ride it around while I finish my other CX500 cafe bike, then start work on a turning my new CB in to a cafe bike.

I've started searching on how to free up a seized engine, I'm hoping the engine in the frame is salvageable and I can have a spare in the shed.  Here's what she looks like:

« Last Edit: December 19, 2011, 10:55:28 PM by enriquez »
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1973 CB750K

Offline Greggo

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Re: '73 CB750 - New project and first CB
« Reply #1 on: December 18, 2011, 05:17:27 PM »
Welcome to the Fourum!  You've got a nice base to start with.  Love that polynesian blue!!
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Offline enriquez

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Re: '73 CB750 - New project and first CB - what 4-1 is this???
« Reply #2 on: December 19, 2011, 10:52:58 PM »
I know a bit about CB's but not much.  I got the engine moving, diesel fuel in the cylinders worked like a charm.  I have tons of work ahead of me, but, I'm really curious about the 4-1 that came with the bike.  Can anyone identify this for me?

It looks like this is gonna be one loud motherf$!%er, anyone have any info???



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1973 CB750K

Offline Retro Rocket

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #3 on: December 19, 2011, 11:30:09 PM »
I am not sure what pipe that is but it will not be very loud or perform to well with that restrictive end plate welded in there....

Try member 754 {Frank}  for pipe identification
« Last Edit: December 20, 2011, 04:15:34 PM by Retro Rocket »
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750 F1 970cc
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Offline lone*X

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #4 on: December 20, 2011, 03:00:41 PM »
Agreed, it's probably going to be reasonably quite.  I would leave the end plate in place until you know what you want to do with the bike as a whole.  If everything else is relative stock, the back pressure provided by the plate will probably make it easier to get running fairly well.  Open the exhaust up and you will start off having to re-jet for the less restrictive open pipe.  Get it running with what you have first, you may be surprised.   Have no idea as to the maker of the pipe.
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Lone*X  ( Don )

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Offline Tews19

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #5 on: December 21, 2011, 07:47:48 PM »
Great looking bike. I saw one just like that listed on CL in San Fran I think for 1200. with another write up with the seized engine and spare. Body of the bike and paint looks really nice.  Welcome to the site.
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1969 Honda CB750... Basket case
1970 Honda CB750 survivor.

Offline ekpent

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #6 on: December 21, 2011, 08:51:21 PM »
Actually the tank looks like a Planet Blue 1975, with the single feed petcock on the left side ?? Have you checked the engine and frame vin carefully to see what year everything is for sure.Post them up here and we can help if needed,lots of swapping went on with these machines over the years.
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Offline enriquez

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #7 on: December 22, 2011, 09:18:48 AM »
Yup Tews, this is that SF bike with the spare engine.  I'm not an expert on CB's, it doesn't surprise me that this may have a mix of parts.  The frame and engine numbers matched the title, I'll post the numbers up here to try and see exactly what I have.  Hope I didn't get screwed here...

ekpent, are single feed left side petcocks unusual for any year?

p.s.  will these captcha's disappear after I've posted a lot??  They're damn annoying.
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Offline ekpent

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #8 on: December 22, 2011, 09:59:33 AM »
Single feed left hand petcock / tank combo's that are held on by a large nut to a tank bung fitting are unique to the 1975-76 K model 750's.Can still be used on earlier models with no problems.
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Offline Tews19

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #9 on: December 22, 2011, 12:33:32 PM »
Just going off looks bike looks very good. If the spare engine runs. You got a nice bike
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1969 Honda CB750... Basket case
1970 Honda CB750 survivor.

Offline 754

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #10 on: December 22, 2011, 11:23:56 PM »
 Looks like a Jardine header...
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Offline enriquez

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #11 on: December 23, 2011, 08:33:36 PM »
Here are the frame and engine numbers:

Frame: CB750-2315594
Engine:CB750E-2200460
Spare Engine: CB75E-2437850

74 frame, 73 engine, 76 spare engine, 75 tank??  A mix for sure, oh well, I wasn't planning on an original restoration anyways.  I was hoping to keep what I thought was the original engine with the frame, but my spare turns over easily so I might as well swap it out.

Are there any differences between 73 and 76 engines?  Any issues with putting a 76 engine in a 74 frame?
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Offline Greggo

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #12 on: December 23, 2011, 08:39:02 PM »
Quote from: enriquez on December 22, 2011, 09:18:48 AM
Yup Tews, this is that SF bike with the spare engine.  I'm not an expert on CB's, it doesn't surprise me that this may have a mix of parts.  The frame and engine numbers matched the title, I'll post the numbers up here to try and see exactly what I have.  Hope I didn't get screwed here...

ekpent, are single feed left side petcocks unusual for any year?

p.s.  will these captcha's disappear after I've posted a lot??  They're damn annoying.

Hey, I'm in Berkeley too!  Let's ride/wrench sometime!
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Offline ekpent

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Re: '73 CB750 - New project and first CB - what 4-1 is this?
« Reply #13 on: December 24, 2011, 06:22:55 AM »
No issues at all swapping those engines,its a plug and play.Difference may be a couple of HP as the engines slowly over the years were detuned slightly for a little more torque and better MPG. Probably would not hardly notice.
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