Author Topic: 1976 CB750A Project Bike (was New Guy with New Project)  (Read 6077 times)

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Offline Rdlbs

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1976 CB750A Project Bike (was New Guy with New Project)
« on: August 20, 2010, 02:29:46 PM »
Hello everyone.  I've been lurking here for a bit, but this is my first post.  I just picked up a 1976 Honda CB750A as a project.  More on that in a minute.  This is my fourth Honda four.  My first was in 1977.  That was a '77 400F SuperSport.  What a great bike that was.  My second was an 81 750k (double OH cam).  My third was a mirror image of that 750k.  This is my first 'A' model.  

The bike has not been registered since 1983, so I'm guessing that it has not been run for 27 years.  That would explain why the engine appears to be locked up.  The good news however is that the bike was stored in a garage for all of those years and all of the parts are there.  Someone added a hideous fairing (the plexi is broken) and saddle bags at some point, probably when the bike was brand new.  Fortunately, the PO kept the original hardware for mounting the headlight and blinkers.  I'll be trying to sell these items soon.  Although the bike is a little rusted here and there, all of the parts being present and a lack of deep rust makes me think that this is a pretty good candidate for a resto.

Anyhow, I thought I would introduce myself and maybe post a few pictures.  I thought maybe I would continue to post my progress if anyone is interested.

Ron






« Last Edit: September 10, 2010, 12:32:45 PM by Rdlbs »

Offline HavocTurbo

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Re: New guy with new project
« Reply #1 on: August 20, 2010, 02:35:29 PM »
Nice start for a project!!

Don't see too many WHOLE A models around for sale.

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Offline hapakev

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Re: New guy with new project
« Reply #2 on: August 21, 2010, 09:42:39 AM »
I'm not a fairing guy, but thats actually a cool looking fairing.  If I were building a tourer, I would put a fairing on it, like that. 

Anybody know what kind of fairing that is?
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Offline Rdlbs

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Re: New guy with new project
« Reply #3 on: August 21, 2010, 10:22:13 AM »
There is a tag on the inside that reads 'WIXOM BROS. INC." from Long Beach, CA.  The fairing and saddle bags will be going on Ebay pretty soon.  If they were painted to match, I would be tempted to keep them.  On the other hand, I want to take the bike back to stock, so these items really don't fit that purpose.

Offline Rdlbs

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Re: New guy with new project
« Reply #4 on: August 22, 2010, 03:05:36 PM »
I was able to take the points cover off of the engine and use a socket to try to turn the engine.  The crank would not turn forward, but I discovered that it would turn backwards, at least half or three quarters of the way around.  Then when I reversed the ratchet and turned the crank back forward, it would turn freely until coming to an abrupt stop at the same place every time.  It really felt to me as if there were something inside of one of the cylinders that was causing the engine to lock up.  Only one way to find out - pull the head.  And only one way to do that - pull the engine.  So, my son came over and helped me yank the engine out of the frame.  While waiting for him to get here to help, I pulled the tappet adjusting covers and found that #3 exhaust valve had about 1/4" of lash!  Long story short, it turns out that the exhaust valve was stuck open.  Of course, I didn't discover that until we had the engine out of the frame and sitting on a bench.  It doesn't matter that I discovered it late - I was going to pull the head to check it out anyway.  Question - since everything looks good other than the stuck valve (I've loosened it up a bit), what is a good way of freeing the valves up and keeping them that way.  I'm pretty confident that the valve was stuck because of having sat for 27 years.  Still, is there some way of treating the guide, especially without removing the valves?

Here are a few shots:

The engine sitting on the bench with the head off.


The cylinder head.


The bores look very good, aside from a little bit of carbon.


Question for the experts - does anything look amiss with the above pics?  It looks pretty good to me, but I don't want to miss something.  Also, when removing the head, these two things fell out.  What the heck are they and where do they go?

Offline Rdlbs

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Re: New guy with new project
« Reply #5 on: August 23, 2010, 12:28:43 PM »
In case anyone was curious about that last picture, I found where they go.  They sit in the oil gallery that feeds the rocker arms.  If anyone needs additional information on them, let me know.

Offline KB02

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Re: New guy with new project
« Reply #6 on: August 24, 2010, 04:43:30 AM »
Yep, those are the oil jets. (just to confirm -since you already figured that out.)

As for the jugs, they look okay to me. Kind of hard to see i the pic, but check for any ridges hat have formed at the top of the sleeve. Sometimes the rings will wear out a groove in the cylinder as they are always trying to expand. As long as it is nice and smooth all the way up, you should be all set. Measure the bore to be 100%, but it looks okay to me.
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Offline Rdlbs

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Re: New guy with new project
« Reply #7 on: August 24, 2010, 06:52:40 AM »
Thanks for the response.  Is the purpose of that orifice to spread the oil or simply control the amount of flow?

I have the head pretty well cleaned up on the outside now.  There was no real staining or corrosion, only some very old oil that was pretty easily removed with paint thinner.  I'll try to get finished with it tonight and post another picture or two.

Offline Rdlbs

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Re: New guy with new project
« Reply #8 on: September 02, 2010, 03:15:14 PM »
I have a few days off of work - I don't have to go back until after Labor day - so, having received the gasket set and other parts that I needed, I went to work putting the top half of the engine back together.  Over the course of the last week or so, I have been cleaning all of the components, including the engine block in preparation for this.  Here I sit, about 3:15 in the afternoon and the engine is complete and ready to put back in the frame.

Before:


After:


Before:


After:


Offline MasterChief750

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Re: New guy with new project
« Reply #9 on: September 02, 2010, 03:32:50 PM »
looks really spiffy i bet it will run as good as it looks
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Re: New guy with new project
« Reply #10 on: September 02, 2010, 04:40:30 PM »
I hope you cleaned up the frame area before dropping the motor back in!

Offline Rdlbs

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Re: New guy with new project
« Reply #11 on: September 02, 2010, 04:47:32 PM »
The engine is still sitting on the bench.  I have been slowly cleaning the frame, de-rusting some of the bits and pieces, painting some odds and ends, etc., while I was waiting for the gasket set to come in.  Tomorrow's chore is finishing the frame and finishing the master cylinder rebuild (the parts arrived today).  In the meantime, I have the first of the four carburetors apart and sitting in the can being cleaned.  I need to do them one at a time, so this will take a while.  Besides, I still need to order the carb kits anyway.  I'm hoping to maybe install the engine a week from Saturday. We'll see . . .

Offline putnaja1

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Re: New guy with new project
« Reply #12 on: September 02, 2010, 06:14:22 PM »
The motor looks great!  You are making some headway!!
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Offline bluesmoke69

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Re: New guy with new project
« Reply #13 on: September 02, 2010, 07:08:46 PM »
Looking good!!

Offline Rdlbs

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Re: New guy with new project
« Reply #14 on: September 04, 2010, 03:05:13 PM »
As I mentioned before, this bike has been sitting for 27 years, or there abouts.  The fuel system was not prepared for storage - I'll post something about that when I get a chance.  I'll be working on the carbs in the days to come.  For now, I rebuilt the master cylinder and the wheel cylinder (caliper).  A note here about cleaning the old parts.  I was struggling to get some of the 27 year old goo out of the brake parts, master cylinder, caliper, hoses, etc., when a friend of mine suggested using water as a solvent to wash away the crud.  That had not occured to me, but since brake fluid is water soluble, that made all the sense in the world.  So, I ran a big bucket of water and let everything soak overnight.  The next morning, all of the crud came out very easily.  Not only is brake fluid water soluble, it also attracts water, much as does diesel fuel.  So, a brake system that has been neglected for long periods of time will show corrosion that can get kind of expensive to fix.  Here are the parts that I took out of the master cylinder.

After cleaning and rebuilding everything, the next step was to fill and bleed the system.  That's more easily said than done.  I fiddled with trying to fill the system, trying to get the master cylinder to prime and if I were a foul man, I would have been cussing up a storm by the time I got frustrated enough to walk away.  See the next post for my solution.

Offline Rdlbs

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Re: New guy with new project
« Reply #15 on: September 04, 2010, 03:16:04 PM »
How I primed and bled the brake system

Hopefully this will help someone else at some point in the future.  Here is what I did, step by step.

1.  Fill the master cylinder with the proper brake fluid.
2.  Place rubber tube on bleeder on the caliper and open the bleeder about 3/4-1 turn.
3.  Get about a 2 - 2 1/2" vacuum cup (like those used on industrial machinery).  Screw a hose into the vacuum cup and screw the other end into an air hose.
4.  Place the vacuum cup on top of the open master cylinder, pressing it down snugly. (I was able to use a couple of clamps to hold the cup in place.  Basically, I pressurized the system from the top of the master cylinder.)
5.  Slowly turn the pressure regulator on the air compressor up.  This only takes about 5-7 psig, so DON'T overdo it!
6.  Watch for brake fluid to start coming out of the bleeder valve.  As soon as fluid starts to flow, immediately shut the bleeder and cut off the air.
7.  Remove the vacuum cup arrangement.  There still should be about 1/4-3/8" of brake fluid in the bottom of the reservoir.
8.  Refill the reservoir and proceed to bleed the system the way you would normally.

Now, I know that one could just go out and purchase a pressure bleeding system.  However, I saw no reason to go spend money on something that I would use once and then stick on a shelf.  I hope this info helps someone else at some point. 

Offline Rdlbs

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #16 on: September 11, 2010, 08:47:40 PM »
I haven't kept this up to date as well as I should have, so this may end up being a bit of a long post.  This afternoon, I fired this bike up for the first time in 27 years.  But before I get to that, let me back up and fill in the gaps since my last post.

Before removing the engine from the frame, we of course had to remove the carburetors.  About 10 years or so ago on another old bike, I tried to go the down and dirty route of simply removing the bowls and jets from the carburetors, cleaning them up and reinstalling.  That didn't work out so well so lesson learned, this time I completely rebuilt the carbs.  I had been told not to separate the four units, but I felt that in order to really do the job right, I needed to work on one carb at a time.  So I separated each carb, disassembled them one at a time and placed all of the parts in plastic bags that were labeled as to which carb it was 1 through 4.  I also took a lot of pictures before separating the units.  Here's a couple of pics in case someone else may need the reference sometime down the road.

I took plenty of photos in order to remind myself of where things went and how to route hoses, etc. Here's the bank with #1 removed.

I purchased a carburetor parts cleaner in a 1 gallon can at my local O'reilly's.  This stuff sure isn't as potent as the stuff we used to soak Holley double pumpers and Rochester Quadrojets in way back in the 70's and 80's, but by letting the carbs soak for 24 hours or so, they came out clean as a whistle. Here's a before shot:

The rebuild is pretty straight forward as long as you mind where all of the orings go.  I have a factory shop manual for this bike and that helps to identify which parts go where.  That along with some of the pictures made this job a snap.  The hardest part was waiting the 12-24 hours while each carburetor soaked in the carb cleaner.  Unfortunately, I didn't get a shot of the carbs after rebuilding, but here's a shot of them installed on the bike.

Since the carbs were done and I had polished and cleaned just about everything that I could find to clean and polish, it was time to reinstall the engine and try to get this thing up and running.  So, my son came over this morning to help me stick the motor back in the frame.  No real tricks here.  The engine went in actually a little easier than it came out.  Oh, I don't think I mentioned in earlier posts that we had a bit of trouble getting the engine out.  We disconnected and removed the carbs, we disconnected the points, we pulled all of the wiring off, we took all the motor mount bolts out, but still we had trouble.  After sweating for a while trying to get the engine out the right side of the frame, we realized that we had forgotten to remove the drive chain.  Duh.  Anyhow, the engine slipped right into the frame and into place with very little struggle.

Then it was time to install the carburetors.  When pulling the carbs in preparations for removing the engine, I had seen a YouTube video showing a guy using a crowbar to pop the carbs loose from their boots.  This is the method that I used to remove my carbs.  I figured if they came off that easily, they should go back on with the same effort if I used the same method.  I greased the inside of the boots up a little bit using a PTFE impregnated grease.  I lined the carbs up and using the crow bar, popped them right back into place.  From there, it was just a matter of installing all of the peripheral equipment.

I wasn't quite ready to install the fuel tank yet - I've been cleaning it out by soaking it with white vinegar.  That method seems to have worked quite well, but it is not yet ready to put fuel through.  So, I jerry rigged a funnel into a piece of tubing and then down into the carburetors.  I filled the funnel with gasoline and let it sit for a few minutes to run down and fill the carburetor bowls.  At this point, I would like to say that I just touched the starter button and away she went.  I would like to say that, but it would be untrue.  I pulled the choke, cranked the throttle a few times and hit the starter.  Although the engine spit just a little bit, it refused to start.  I used a can of starter fluid (I had not installed the air cleaner yet) and still no dice.  I took #4 spark plug out and checked for spark.  Although the spark was not terribly hot, it seemed me to be pretty normal for a non-electronic ignition.  Reinstalled the plug and cranked it some more.  Finally, finally, I started to get some response from this long dormant engine.  It sputtered a bit, it back fired a little, it over ran the starter motor and then it roared to life!  Very quickly, I was able to get it warm enough to idle.  I do need to adjust the idle mixture screws on the carburetors.  Right now, they are on the initial setting of - according to the book - lightly seated and then 1 1/4 turns out.  There will be plenty of time for that later, but for now I am very happy to report that the engine runs perfectly.  No undue noises, everything seems tight.  No smoke at all.  Oil pressure came right up while I was still cranking the engine.  Everything really seems perfect.  I could not be happier with it!  I stuck the tank on at my son's request, just so we could take some pictures.  Here's what we are looking at now.  The tank still needs to be waxed and cleaned on the outside and the front turn signals and headlight need to be finished up. Other than that, there's not a whole lot left to get this thing on the road.
 



And just as a reminder as to what we started out with on August 20th:



I can't wait for my first ride!!

Offline Old75_ratafe

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #17 on: September 11, 2010, 10:43:28 PM »
<------- Officially jealous  ;D
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Offline Rdlbs

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #18 on: September 12, 2010, 07:27:57 AM »
I just realized that you can click on the pictures for a bigger view.  That will open up a new window that goes to Webshots.  There are more pictures there that I did not post if anyone would like to take a look.

Offline Rdlbs

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #19 on: September 16, 2010, 07:26:04 PM »
Hopefully some of you guys will still be following this thread and can help me out with a little problem.  As posted above, I got the engine running.  It sounds good, has good power and starts well.  I have been monkeying with the carburetors, trying to get the idle correct.  Here are the symptoms:

Engine warm:

1. The idle will be smooth but then will dip and it sounds like I am losing one cylinder.

2.  If I then give the throttle a rap, it will rev up and then come back down very slowly, sometimes staying higher than before I gave it gas.

3. Once I shut it off, even when the enging is fully warm, I need to use the choke in order to get it started again.

4. When I put it in gear (it is an auto), the rpms dip so far that it stalls the engine.

Anybody have ideas what to check?  These carbs were all four completely cleaned out, including soaking in the tank as described above.  Am I just that far off on the idle mixture?

Offline Old75_ratafe

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #20 on: September 16, 2010, 09:26:25 PM »
did you change anything?  air box is back on right?  I don't know as much about these carbs but I do know they don't react well to modifications from the posts I have seen.  Leaks in the boots will cause problems.
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Offline raymond10078

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #21 on: September 17, 2010, 06:42:19 PM »
Did you check your solenoid and dashpot?  The A's have a solenoid that is controlled by the gear selector switch (via a relay, I recall) - so that when the bike is in gear, the solenoid is energized.  When energized, the solenoid allow carb vacuum to be applied to a dashpot (or diaphram), the opens the throttle a little (just a little bit off of the idle stop).

You should be able to see if this is working, but either watching the dashpot, or watching to see if the carbs open slightly (off of the idle stop).
1978 CB750A (upgrading very, very slowly)

Past bikes - Honda: SL350, CX650C, CB900C, CB1000C, CM450A; Kawasaki: several 1972 750 H2's; Suzuki: TC90J.

Bikes I want: CX650ED, a mid-sized japanese V-twin with ABS.

Offline Rdlbs

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #22 on: September 17, 2010, 09:13:45 PM »
I started looking into that system this afternoon.  I have determined that the check valve is working properly and the dashpot is working properly.  However, the solenoid seems to not be working.  I'll take a closer look at it tomorrow to make sure that current is getting to it.

In order to start looking around at that idle control system, I had to take the tank back off and jerry rig my fuel feed funnel and hose back onto the bike.  With the tank removed and the temporary fuel feed hooked up, the bike ran great, even when I put it in gear, although it obviously lugs down a bit.  I kind of wonder if I may have had some kind of kink in the fuel hose coming out of the petcock?  I have an inline filter, so the hose had to take a bit of a circuitous route from the petcock to the carbs.  I'll reroute all of that tomorrow also to see if that makes a difference.

I'll try to post some pics tomorrow and I'll let everyone know what I discover.  I'm a little pinched for time because I am getting ready for vacation, shopping, etc.  But we'll see what I can get done.  Thanks for your responses!!

Ron

Offline Rdlbs

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #23 on: September 18, 2010, 05:12:24 PM »
Sorry, but I didn't get any pictures.  There was really nothing particularly interesting to shoot.  I did take a little short ride this afternoon, just down the street and bag.  The bike bogs really badly (accelerator pump works fine) and I really have to feather the throttle in order to get any RPM's.  I swear, it acts like it's starving for gas - at least part of the time.  Then it will run fine.  Then it acts starved again.  I don't have much hair to pull out . . .

Suggestions as to what could be causing this?  Float levels?  Sticking float or float valve in one carb?  I do notice that gas does not seem to be flowing through the clear plastic fuel filter that I added.  Then all of a sudden, gas will rush through it.  Then it seems to stop flowing.  Is this pretty normal?

Oh and as a PS, it starts fine without the choke now.  Hmmm . . .
« Last Edit: September 18, 2010, 05:15:15 PM by Rdlbs »

Offline Grnrngr

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Re: 1976 CB750A Project Bike (was New Guy with New Project)
« Reply #24 on: September 18, 2010, 06:29:55 PM »
Nice looking bike and great cleanup on the motor! don't have any suggestions about the bogging issue, but I'll be watching as I'm sort of in the middle of getting my '77 A back together as well. I'm afraid mine needs new clutches tho...pulled the pan as part of trying to figure out why it won't go into high gear, and found little chunks of non-metallic stuff. Great to see another Hondamatic owner here...the Hondamatic.com forum died not long ago..
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