Topic: 78 CB750K build, should be interesting.

[Sheik Yerbouti]

Hey guys. Some of you may have already seen my documented hunt for a cheap bike in my area. I ended up with a '78 CB750k, with around 25k on the clock. It's not running, needs the carbs cleaned and a new exhaust, but it was 300 dollars delivered to my door, so I can't complain too much. He also threw in an extra seat pan, an old rusty tank, a new set of clubman bars, and the two cracked side covers. This is what she looked like when we first saw her.



So, it's been sitting in my garage for a week, and I just started to get some things done. We gave it a bath with some simple green, but it'll certainly need a lot more cleaning when I start tearing it apart. Right now the goal is to get it running.

From what I know, this is what I need to get it running. The carbs need cleaned, it needs a battery, and it needs the exhaust. I am going to probably go Mac 4-1 (it's cheap but it'll work). I noticed the headers are missing a stud, is that something special that I need to get or can I find something at the hardware store? The carbs are proving to be a pain in the butt to get off. The screws on the hose clamps on the rubber boots are stripped.  Any suggestions for getting those out? I plan on investing on an impact driver soon as well. I'm also missing a few screws from the chrome covers on the engine. I'm going to go to a local hardware store and see if I can get some stainless fasteners. Here's some pictures for the bike in question.







Here's those carb screws.



A few ideas for what I plan on doing.

Satin black tank, satin black frame, chrome bobbed fenders, silver and black engine paint, black seat cowl with a cafe seat. I want this bike to be as simple as possible. I was thinking of a way to vacuum form my seat cowl out of smoked plastic, and hiding my turn signals and tail light in the cowl itself (maybe using LED lights? I'm still figuring it out). But I want this to be a no frills rider.

I appreciate your comments guys.

[martino1972]

congrats on the buy,looks good for not alot of money...

[eurban]

Your carbs on non stock.  They appear to be from a pre 77 750.  What's the engine number?

[Sheik Yerbouti]

Where would I find the engine number? We have no light in the garage so I can get you the number tomorrow?

Pre-78 carbs eh? That should make rebuild kits a lot cheaper. Yay!

[Hush]

Hey nice start to your project, that bike has got good bones.
Carbs...s.....honda carbs...titter titter.......welcome to Hell my friend.
My one suggestion is once you have wrestled (and hopefully won) them off the bike, replace the small cross head screws that hold the float bowls on with hex head screws (allen keys).
You will thank me after your 5th bowl removal when the carbs leak/block/need rejetting etc.......happy Halloween!

[KB02]

I noticed the headers are missing a stud, is that something special that I need to get or can I find something at the hardware store?

You can still et them from Honda. As for the hardware store, it depends on the store. Some might have them in the right size and thread. Others might not.

As for your carbs, yeah, they are Pre-77. In 77 the moved the choke to a knob on the handlebars rather than that lever on the side. Don't worry about the screws that Hush mentioned, as you don't have them (Although if you did, he'd be right... I changed them on mine). You've just got a latch that you can pop off with your fingers (strong fingers... or maybe a flat head screw driver...)

Engine number you will find located on the top of the back side of the engine on the right. Should read CB750E-xxxxxxx; or something like that.

[Sheik Yerbouti]

I checked the engine number. It's CB750E-3013143

That indicates that it is '78 engine, right?

Engine: CB750E-3000001 

[andy750]

If the carbs have been changed be careful that the carb-engine rubbers have also been changed...if not you`ll be chasing air leaks as the 78 rubbers were different for the different carbs).

Good luck - looks like a good project and no doubt like the rest of us you`ll end up spending more than you thought!

cheers
Andy

[Sheik Yerbouti]

I found a guy on craigslist selling an exhaust for a 76F, is that interchangeable with my 78K? It looks to be in alright condition and the price is right.

[eurban]

Assuming that it is a stock 76 exhaust, you will need to remove your exhaust studs, locate a set of spiggots and bolts from a pre 77 bike, and install them on your 78's head.  You will also need the pre 77 flower clamps.  You will then be able to mount the earlier exhaust to the head but it wont be a direct bolt on at the rear.  You will need to fab up a support bracket of some sort.  The stock 75/76F model 4-1 exhaust is sturdily built but is heavy and not particularly high performance. . . .

[KB02]

Assuming that it is a stock 76 exhaust, you will need to remove your exhaust studs, locate a set of spiggots and bolts from a pre 77 bike, and install them on your 78's head.  You will also need the pre 77 flower clamps.  You will then be able to mount the earlier exhaust to the head but it wont be a direct bolt on at the rear.  You will need to fab up a support bracket of some sort.  The stock 75/76F model 4-1 exhaust is sturdily built but is heavy and not particularly high performance. . . .

That's not entirely true. My 76F used the same stud system for the exhaust as the 78K does. Same flowers and collars and everything.

I agree with everything else, though. There were times when I would say to myself, "If these pipes were just a bit more free flowing..."
http://i152.photobucket.com/player.swf?file=http://vid152.photobucket.com/albums/s182/actorextreme/04-21-07_1932.flv

[Sheik Yerbouti]

If I can get it for a good price, I'll just take it. I don't have money to dump into an exhaust, so something like this will be great for now. I'll just use a good paint and give it the old spray bomb.

[eurban]

Assuming that it is a stock 76 exhaust, you will need to remove your exhaust studs, locate a set of spiggots and bolts from a pre 77 bike, and install them on your 78's head.  You will also need the pre 77 flower clamps.  You will then be able to mount the earlier exhaust to the head but it wont be a direct bolt on at the rear.  You will need to fab up a support bracket of some sort.  The stock 75/76F model 4-1 exhaust is sturdily built but is heavy and not particularly high performance. . . .

That's not entirely true. My 76F used the same stud system for the exhaust as the 78K does. Same flowers and collars and everything.

I agree with everything else, though. There were times when I would say to myself, "If these pipes were just a bit more free flowing..."
http://i152.photobucket.com/player.swf?file=http://vid152.photobucket.com/albums/s182/actorextreme/04-21-07_1932.flv

Sounds like Honda switched to the "newer" system for mounting the pipes on the first F models.  I stand corrected . . .

[KB02]

Yeah, the F's were always the red-headed step children of the family.   

[MRieck]

Yeah, the F's were always the red-headed step children of the family.   

I don't know about that.......

[KB02]

Well... I've always had a thing for redheads anyway...   

[dimesack65]

I just put a 4into1 header on my 78' 750. One of the studs had been previously stripped out(I'm assuming that it was jb weld on the threads). I read in the archives that one member broke a stud and drilled and tapped it. he noted a 17/64ths bit and a 8mm X1.25 tap. Apparantly he drilled the stud and retapped the threads, as my 8mm tap slipped in and out with ease. I ended up using 21/64ths bit and a 10mm X 1.50 tap and it worked out nice. I started with a 40mm bolt but it bottomed out when I reassembled it so I went back with a 30mm bolt.

[Sheik Yerbouti]

This project is coming back from the dead. Like a zombie, except maybe a bit less brainless. Actually I don't even know.

Well, the reason this bike has been untouched for a year is because of school school and more school. I hardly had time to pee in the last 5 months.

I don't start my internship until the end of the month, giving me a little over a week to get some stuff done. The fun part is I'm broke as a joke. So I am going to be working on the things that cost a bit less, you know? Tomorrow I am going to Kinkos to print out the Honda manual I have on PDF, and getting busy. Firstly I am going to run to harbor freight to buy some of those handy plastic drawers, so I can label everything and keep it all tidy. I think they were on sale last time I checked.

Things wrong with the bike:

1. No exhaust (I know I know), but I do have the headers
2. Airbox has mice in it
3. Tank is rusty, and the lock has been busted out (I think I'm going to have to rig some sort of lock from an auto store or something, that's not a huge concern right now.
4. No battery
5. Everything looks like hell
6. Unknown state of the electrics, things look disconnected
7. The stator cover (I think, it's the one on the left side if viewing the bike from behind) looks...dented. Like it was dropped. How concerned should I be? The dent isn't huge but it's there. I'm hoping the dent itself is just on the cover, and didn't hurt anything behind it.

So, things that I can do with little to no money in my pocket. I have a big thing of rust remover, I can clean the tank. That's a start. I'll hammer some knee indents in it too. I really don't think too highly of the 1978 tank, it looks kind of silly. But with some well shaped indents, I might be able to make it look a bit cooler. The lines of the tank aren't that bad or anything, but they could be punched up with a bit of style. I'm a design student so I can do some quick models and see what looks good.

I guess I should tackle the carbs ASAP, to get it running. But as it stands, I don't have enough money to rebuild them. Is it worth taking them apart and just cleaning them or should I wait until I can afford the kits? I know the po' boy kits are available, but I'm not sure what all I'll need. I guess I could take them apart and leave them in pieces, but I kind of wanted to avoid that.

I have a 1976 seat pan, which I understand is different (hinge on the opposite side?), but I was going to build my seat off the pan, because the 1978 seat is still fairly decent looking. I really REALLY hate the large turn signals and tail light, so I was thinking of modeling the cowll up in 3D, milling a form, and then thermoforming a plastic cowl to fit. I know more about that than I do about fiberglassing. I can paint the cowel black, but leave parts of it clear and enclose my tail light and signals in it, maybe fab up a bracket or something. I think that'd be slick. But then again, it'd be better on a running bike eh?

Eh, just some musings and thoughts. I just got my camera back today from a friend, so I'll be a-snapping tomorrow. I should have some 3D stuff done too, some concepts for cowls and tanks.

[Sheik Yerbouti]

Teardown today. Removed everything but the engine, carbs, and oil tank. Having a bit of trouble sort of "rocking" the carbs off. I got all the bands off, but the rubber is really effing on there.

Here's some progress pictures, with the clubmans on.









And here's that "dent" I'm worried about.

[Sheik Yerbouti]

Oh yeah, I was also curious, are those carbs infact from an earlier model?

[mystic_1]

Oh yeah, I was also curious, are those carbs infact from an earlier model?

If you look at the top side of one of the carbs, right where it meets the mounting plate, there's a flat boss with a casting number stamped in it.  Look it up on this chart:

http://www.sohc4.net/index.php?title=FAQ#Settings_Guides

mystic_1

[Sheik Yerbouti]

Carbs cleaned and adjusted. Headers are coming today, should have it firing by tonight if the good lord smiles upon us.

[Yak]

Hello all,

I'm going to pirate this thread for the next few months as my friend and i have been working on this bike for a bit now, seeing as he is halfway across the country and it's sitting in my garage, i figure i'll continue work on the project until his return. I'm sure he'll be chiming in just as much as I on this thread, so expect the activity to rise a substantial amount.

As it stands now, our next step is to get the engine to turn over and possibly fire. There are a set of headers and an exhaust en route, and a battery to soon be purchased, i'll update with some new pictures as soon as the headers and exhaust arrive.

yak

[Sheik Yerbouti]

Now that I'm not broke as a joke the parts are starting to roll in.

Tomorrow I am ordering new float bowl gaskets for the carbs, the old ones are hosed. Totally dry and cracked.

Just bought an exhaust on the cheap from a fellow forumite. It's a '74, but he's including the spigots and the collars, so hopefully things will interface just dandy. If not, you'll get a nice panic thread from me or Yak.

Battery is going to be an ebay purchase, it looks. Then after that it's gravy/cosmetics/new chain/whatever else might kill me unless I replace it.

[Sheik Yerbouti]

Good news everybody!

Battery ordered.
Exhaust on it's way.
Float Bowl Gaskets ordered.

So, this is the deal with the exhaust. I bought it through a wonderful fella on this forum, it was labeled for the "budget conscious". That was perfect for me! They're 4-2, dirty/rusty in spots but have no holes or weak spots, and I guess the number 3 has some carbon in it that needs taken care of. From what I understand, carbon can be removed with heat (torch it until red hot and chip at the carbon with a screw driver. The other alternative is something like oven cleaner to see if it can dissolve some of that carbon, then cleaning out the headers real nice and seeing what happens. Any experience doing anything like this?

The exhaust is a '74, so he included the spigots from an earlier model CB750 in the box. So we're going to have to replace the spigots in order for the exhaust to fit, correct? We're also missing an exhaust stud. A quick search leads me to believe the correct size is 6mm by 45mm long. We might be able to find that at the local nuts and bolts store, I assume they're hardened or stainless or something? And is there some sort of copper gasket that goes between the engine and the header pipes?

I know it seems like hell of a lot of questions, but I haven't seen the stuff yet. Yak is back home with the bike, salivating, waiting to work on it. And he's going to receive all the parts by the end of the week. If he has any additional questions he'll bump the thread.

Pictures of the exhaust. I plan on wrapping the headers and painting the rest with VHT paint.