1981 CB750 Cafe Build Project

[Jefe06]

Hey guys.  I've been a long time read of the forums and now I will actually be able to use all of the information I've gotten from reading all of your posts.  I've had my mind set on getting a CB750 for a couple of years now, and just recently one found its way to me.  My uncle is one of those guys who purchases a lot of stuff and doesn't know what to do whit it once he has it, but I was telling him how I wanted to make a cafe racer out of a CB750 and he said he had one that he had no plans for and would give it to me.

 It's in a bit of ruff shape, but the other day I managed to get it to my pops garage and started giving it a once over. I'm not sure how king it's been since it was started but apparently it ran fine but had a little fuel leak.  Based on what my uncle told me I think it may have been something small like a bad petcock or fuel line.  Well we hooked it up to a site own lawn mower battery and tried seeing if it would turn.  We tried a couple of times and after turning the engine for about 3 secs three separate times, it drained the battery, then even with a good battery it wouldn't turn.  We check the connections for the starter, solenoid, and ground cables.  We cleaned them up and wouldn't you knot it it started turning a it stronger, but it still killed the battery after turning for about 3 seconds on two separate tries.  I wasn't alble to see if it would fire since the tank was missing the petcock.  that may have been the prev owners fuel problem!!! Ha.  Any advice with getting the starter to be more efficient would be great.

Anyways based on what I've read and what I've gotten from speaking with some people I am going to check the compression before trying to fire it up.  I'm pretty sure I will need to redo the carbs and I have ordered then rebuild kits.  If the compression is goodmim not going to plan to crack open the engine.  The crabs will prob need to be rebuilt, which I've already order the kit for.  The factory manual is pretty comprehensive so I fell OK doing the carbs myself.

Several other things will need to be done, but I'm looking forward to getting it running and putting it through its paces.  I will keep coming back to this forum as you guys are very helpful, knowledgeable and have a good community here.  I'm pretty excited to get this project going.  Any advice to get it running will be appreciated.  Will post pic soon.  I'll be around, so see you guys.

[shinyribs]

Welcome former lurker!Good to have you. I love build threads.Lots of pics!!!! Good luck with your project.

[Jefe06]

Thanks shiny.  I guess one other question I have is about replacing the if I should change over to blade fuses or stick with the glass bulbs.  Is there a blade fuse block that will fit below the central handlebar housing?

[shinyribs]

My bike is a SOHC and apparently the worst ones in need of a blade type fuse box conversion. I'm still riding on the factory setup. But,lucky me,my fuse block looks like brand new. I had an issue with my main fuse blowing for a couple weeks and was gonna swap over to blades. I tore into the bike to do it one day and found  pinched wire. So I'm still rocking the glass fuses now I cant find anything wrong with my fuseblock.All the brass is still nice,yellow and shiny.Nothing there to cause an issue.It really all depends on what kinda shape yours is in. On the other hand,it never hurts to upgrade!

[rrgunslinger]

I just soldered the blade type fuses onto the old connectors.  If you don't have a wire problem this may work for you. 

http://i373.photobucket.com/albums/oo172/grandpaslinger/CB%20750/100_0577Large.jpg

On Fri, Jun 29, 2012 at 12:31 AM, shinyribs [via Honda CB750'S] <[hidden email]> wrote:

My bike is a SOHC and apparently the worst ones in need of a blade type fuse box conversion. I'm still riding on the factory setup. But,lucky me,my fuse block looks like brand new. I had an issue with my main fuse blowing for a couple weeks and was gonna swap over to blades. I tore into the bike to do it one day and found  pinched wire. So I'm still rocking the glass fuses now I cant find anything wrong with my fuseblock.All the brass is still nice,yellow and shiny.Nothing there to cause an issue.It really all depends on what kinda shape yours is in. On the other hand,it never hurts to upgrade!

Montvale,Virginia
 Piute said it best:  "wheres my 10mm?"
Hellbilly-"that is a great way to tell if you have come to your senses, when you start drilling random holes in things... "

LukeM-"Scooters rock, especially when they're in posse formation. "

Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato

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[Jefe06]

RR, yeah that was a thought of mine.  I probably will end up doing that since my wiring (other than at the connections) is in decent shape.

As for an update my my current project.  I manager to run a compression test on all of the cylinders.  I have kind of mixed feelings about the results, but the bike has been sitting for awhile and I think that one of the exhaust valves maybe gummed up.  On cylinders 1-3-and 4 I got about 150 psi max with throttle wide open.  The #2 cylinder gave me something like 90 psi.  I ddin't check it by putting some oil in the cylinder and rechecking the compression, but I do think that the exhaust valve may be leaking.  Ijust have to get the bike running and put it through its paces before knowing if any malfucntions is from just sitting or actual damage.

I pulled the carburators off and they are pretty well gummed up not to mention the No.1 cylinder is missing the float bowl and floats, among other things.  I have a set of carb rebuild kits and with the help of this forum and the FSM I will be getting them back to where they need to be.  

I got the engine to fire and run for a feww seconds today with some starting fluid.  It really sounded good, but I wont be able to tell definiativly until i get everything running fine.  I connected the bike to a car battery today and it turned over fine and fired.  I'm just not sure if the starter will have enough power to turn the engine if I use a new bike battery.  Any help with getting the starter more juice would be greatly appreciated.

It also looks like I have a leak on the valve cover just above the the No.1 carb.  I will need to address this as well.  How do you guys feel about liquid gasket?

Homework for the next week or so will be to get the carbs in operating condition and get a float and float bowl.

[shinyribs]

Sounds like you are on the right track. The low comp on one cylinder is most likely a valve issue,like you said.Pretty rare for one cylinder to wear down that much more than the rest.

The only gasket maker/silicons I have ever had any success with is Permatex Ultra Black. Not the shiny.glossy looking regular black.Gotta be Ultra Black.This stuff is totally unaffected by oil. I used it to seal my vlavecover a while back.


Those first few seconds of one running are just the best!!!

[Jefe06]

Shiny, you aren't kidding.  Those few seconds are gonna keep me going though this thing.  Its kinda like golf, which i really don't find that fun, but no matter how many terrible games you play, one solid sweet shot will always have you coming back for more.

Quick update.  This evening I started to go through my carbs to see what condition they were in.  I only did one and took it slowly to make sure I soaked in everything.  When I turned one oF the carbs over a bunch of dry whit chunks came out of cam out.  The carb wasn't in too bad shape.  The puck and floats are cleaned and operating now.  I will need to take the carb appart again to install the replacement rebuild pieces, but I'm gonna take my time and assess each carb before replacing anything.


Oh yeah almost forgot.  When I was taking the carb bank apart one of the throttle controls had a typical spring installed but another part of the throttle control had a really flimsy lightweight spring and I wasn't sure of the is something the PO had Jerry rigged up.

I'll be posting sme pics tom.

[Jefe06]

So on Monday I slowly took apart one of the carbs just to figure out what was what and what went where.  I reassembled it the same night and put the task of cleaning the first one off till this eveneing.  I completely disassembeld one earlier today and let me tell you everything was gummed up way beyond what I thought it was going to be.  The float needle was jammed so sightly in the housing that even with all the WD-40 and a pair of needle nose pliers i had to yank and pull until it finally came out.  I am currently having trouble getting the air jet out of the puck.  I've tried putting some penetrating oil into the puck, but havent been able to work the air needle loose.  Oh, and the fuel rails had so much crap in them.  I was happy once I got them back to whistling dixie.  Everything is currently in the bath and I hope it will be good to go tomorrow. Then I will tackle the next carb.

Can someone tell me the what the point of the slow speed jet is since it is plugged by the rubber stopper?
Also any ideas to get the air needle loose would be greatly appreciated.

Does anybody have any idea what to use to get stains off of the outside of the carbs?

Happy fourth guys!

[shinyribs]

The rubber stopper you mention sounds like the float needle. I think you might have accidentally confused those two.

For the stains you can use The Works toilet bowl cleaner. READ THIS: DO NOT USE THE WORKS ON ANYTHING CHROME!! IT WILL RUIN THE PLATING!!!

I clean my carbs inside and out with this stuff,except my bowls cuz of the chrome finish on them. This pic shows a carb main body i soaked in a 4-1 diluted solution (4 parts water/1 part Works) and let soak for 30 seconds.Zero scrubbing. A $2 bottle of this stuff will last for years cleaning carburetors.

[Half-Caf]

Jefe, just finished rebuilding my carbs last night. Seestheday found a great tutorial with pics a while ago. I printed it out and it made quite the handy reference.

Jefe06 wrote

The float needle was jammed so sightly in the housing that even with all the WD-40 and a pair of needle nose pliers i had to yank and pull until it finally came out.  

That's bad! be sure you polish those needle seats before sticking anything back in there! You may need new needles, too..

Jefe06 wrote

I am currently having trouble getting the air jet out of the puck.  I've tried putting some penetrating oil into the puck, but havent been able to work the air needle loose.  

Do you mean the slides?

If so, have you removed the large screw down inside the piece? Your slide needles should have some play in them actually. The screw is what holds them in.

Jefe06 wrote

Can someone tell me the what the point of the slow speed jet is since it is plugged by the rubber stopper?
Also any ideas to get the air needle loose would be greatly appreciated.

 I can't tell you exactly how it works, but I believe there is a small hole that goes into the slow jet tube underneath the plug.
And yes, Shiny, its supposed to be there

[shinyribs]

I learn something everyday...at least thats the plan.Sorry for my half-witted reply Jefe