Topic: 78 CB750F "Modular-ish" cafe build?

[madScientist]

The goal was to make this a cafe style bike that could be "converted" back to being the standard tail if I decided to ride 2 up. I made the seat perch boltable so that I could remove it accomodating for the cafe tail. I also made it so the seat lock could be added and removed as necessary. The bike got mostly new everything. The head was a stage 3 job by Mike Rieck who most of us hot rodders are familiar. I installed a DP836 kit from Dynoman. It has a megacyle 125-65 (i think) along with Mikuni RS34 carbs. The pipes are cycle x. ARP studs and stainless scews throughout. I updated the front brakes to a set from a DOHC bike and a Brembo master for a little more stopping power.

The front springs are progressive and the back are Ikons. I had plans to upgrade the rear brakes to a dual piston set but never got around to it. I added a Tarozzi fork brace for a little more stability on the front end. I toyed with swapping the rims out for a GL1000 configuration but grew fond of the Comstars. Reminds me i need to inspect the rivets.

What you dont see is i added a wideband to the HUD and changed the faces to black. I think most everything about it has been shown. There's a lot of other little things that I just cant remember at this point. The thing has been a great riding, reliable, and fun bike.
Link to the gallery: https://postimg.cc/gallery/yHmLtNj

[madScientist]

Just got the carbs back from JimF who welded the post back on. The man does fantastic work and saved these carbs.

I have them mostly cleaned and back together. Hopefully finish that up in the next couple days and see if the ol' girl will make some noise!

[grcamna2]

Just got the carbs back from JimF who welded the post back on. The man does fantastic work and saved these carbs.

I have them mostly cleaned and back together. Hopefully finish that up in the next couple days and see if the ol' girl will make some noise!

I would like to see his repair on your carbs 

[madScientist]

I would like to see his repair on your carbs 

Ask and ye shall receive. The post lines up real well and the weld looks solid. I tapped all the pins lightly with a brass punch to get them to see and it held up solid.

Next up is float level check, bench sync, and see if the bike will breathe some fire.

[grcamna2]

That's a solid weld;glad you saved those great Mikuni carbs.

[Godffery]

 Well I just now came across this thread!
I've got a set of those same Carbs for a 74 750 / 836 project, but have had major fitment issues. 
I haven't gone threw all the previous pages yet, so this might have been discussed already?  If so, could you save me some time and point me to the page.

[madScientist]

Well I just now came across this thread!
I've got a set of those same Carbs for a 74 750 / 836 project, but have had major fitment issues. 
I haven't gone threw all the previous pages yet, so this might have been discussed already?  If so, could you save me some time and point me to the page.

Do you have an F or a K model? The F2's were blessed with a slightly more pronounced curve in the intake spigots (things that you push the carbs into). I had to hit them with a heat gun and get them good and hot so they'd be pliable enough to jam the suckers on there.
Then clamp them down really good.

But, before you even try to get them on, make sure the floats are all 17mm from the base. Thats how they come from the factory but accidents happen. Then set your mixture screws on all of them to 2-3 turns out. I do 2 1/2 or 5 half turns as a starting point.

Then...bench sync them by taking a drill bit and sliding it under the #3 slide and setting it so that it slightly drags on the bit. The #3 slide is hard set from the factory and you cannot adjust it so it's your balance point. Adjusting the slides requires taking the top covers off and using a 12mm wrench and phillips screw driver to adjust the jam nut. Counterclockwise raises the slides, clockwise lowers (i think).

[Godffery]

Well I just now came across this thread!
I've got a set of those same Carbs for a 74 750 / 836 project, but have had major fitment issues. 
I haven't gone threw all the previous pages yet, so this might have been discussed already?  If so, could you save me some time and point me to the page.

Do you have an F or a K model? The F2's were blessed with a slightly more pronounced curve in the intake spigots (things that you push the carbs into). I had to hit them with a heat gun and get them good and hot so they'd be pliable enough to jam the suckers on there.
Then clamp them down really good.

But, before you even try to get them on, make sure the floats are all 17mm from the base. Thats how they come from the factory but accidents happen. Then set your mixture screws on all of them to 2-3 turns out. I do 2 1/2 or 5 half turns as a starting point.

Then...bench sync them by taking a drill bit and sliding it under the #3 slide and setting it so that it slightly drags on the bit. The #3 slide is hard set from the factory and you cannot adjust it so it's your balance point. Adjusting the slides requires taking the top covers off and using a 12mm wrench and phillips screw driver to adjust the jam nut. Counterclockwise raises the slides, clockwise lowers (i think).

Thank you for the tips on that.  The bike in question is a 74 K model, and I will be using the 77 / 78 late model intake boots, as they have the larger O.D. to fit the 40mm spigots on the carbs.  Still the largest issue has been proper spacing of each Carb body, so I am making all new mounting brackets, Throttle Shaft and fuel rail tubes, as well as some modifications on other bits to cram #3&4 carbs closer together. 
 I've got a few pix of the project here https://www.instagram.com/godfferysgarage/ if you cart to have a sneak peek. 

[madScientist]

Thank you for the tips on that.  The bike in question is a 74 K model, and I will be using the 77 / 78 late model intake boots, as they have the larger O.D. to fit the 40mm spigots on the carbs.  Still the largest issue has been proper spacing of each Carb body, so I am making all new mounting brackets, Throttle Shaft and fuel rail tubes, as well as some modifications on other bits to cram #3&4 carbs closer together. 
 I've got a few pix of the project here https://www.instagram.com/godfferysgarage/ if you cart to have a sneak peek.

Did you buy them spaced or are you spacing them yourself? I bought mine pre-spaced and ready to go from CycleX so I didnt have to futz with the madness of getting them spaced right so I'm not sure i'll be much help in that department. My rack looks like they moved the bodies in as far as they would go.

[Godffery]

Thank you for the tips on that.  The bike in question is a 74 K model, and I will be using the 77 / 78 late model intake boots, as they have the larger O.D. to fit the 40mm spigots on the carbs.  Still the largest issue has been proper spacing of each Carb body, so I am making all new mounting brackets, Throttle Shaft and fuel rail tubes, as well as some modifications on other bits to cram #3&4 carbs closer together. 
 I've got a few pix of the project here https://www.instagram.com/godfferysgarage/ if you cart to have a sneak peek.

Did you buy them spaced or are you spacing them yourself? I bought mine pre-spaced and ready to go from CycleX so I didnt have to futz with the madness of getting them spaced right so I'm not sure i'll be much help in that department. My rack looks like they moved the bodies in as far as they would go.

These were also purchased from Ken at CycleX, but the order was placed and received 3 years ago (Yeah, I'm only now getting to this stage of the build, due to health issues) so after talking to him about this, he says his "older" RS Carb kits were not as close, but has since improved the fitment. But even those are not a perfect alignment, and average about 3mm off. Well long story short, After talking to another dealer in Australia that also sells kit's for the CB750, I determined that with some substantial work, they can be re-spaced dead on. So that is where I'm at now, and almost finished making the necessary parts.

[madScientist]

Well good luck on getting those set. My RS's were purchased in 2012 and popped on without a whole lot of fuss save for the spigots being hard as a rock. I'm real glad now that I was able to get them repaired cause I was about to venture into getting a KZ set and spacing them myself based on the ones I have...which i was not looking forward to doing even a little bit.

[grcamna2]

I would like to see his repair on your carbs 

Ask and ye shall receive. The post lines up real well and the weld looks solid. I tapped all the pins lightly with a brass punch to get them to see and it held up solid.

Next up is float level check, bench sync, and see if the bike will breathe some fire.

I need to repair an old XL dirtbike OEM carb-top with the threads.. so I plan on removing a good threaded section off a parts carb body and somehow epoxying it on to my other carb's slide bore.
Have you ever used a strong epoxy on a carburetor ?

[madScientist]

I need to repair an old XL dirtbike OEM carb-top with the threads.. so I plan on removing a good threaded section off a parts carb body and somehow epoxying it on to my other carb's slide bore.
Have you ever used a strong epoxy on a carburetor ?

I have used marine epoxy, jb weld, devcon, and several others. If its not going to be exposed to gas, any of those would likely work okay if you scuff the snot out of it in advance. If it will see gas, the epoxy will eventually fail.

Although if i'm understanding what you're wanting to do correctly, you're going to need to be really precise on the splicing or your slides going to bind. Might be a better option to get a good donor carb body imo.

[grcamna2]

I need to repair an old XL dirtbike OEM carb-top with the threads.. so I plan on removing a good threaded section off a parts carb body and somehow epoxying it on to my other carb's slide bore.
Have you ever used a strong epoxy on a carburetor ?

I have used marine epoxy, jb weld, devcon, and several others. If its not going to be exposed to gas, any of those would likely work okay if you scuff the snot out of it in advance. If it will see gas, the epoxy will eventually fail.

Although if i'm understanding what you're wanting to do correctly, you're going to need to be really precise on the splicing or your slides going to bind. Might be a better option to get a good donor carb body imo.

I understand.
I've looked for a donor carb body but they aren't anywhere available..
I'm seeing that JBWeld makes lots of new products(2-part epoxies)besides their old standard 2-part grey tubes which I'm used to;maybe one of those might work.

I cut the section of the threaded top part off just shy of the inner machined slide bore so the slide won't touch that area.
I took it to my welder this morning and he told me if he tig welded it that the threads might get some damage.
I asked him if he had a tiny little tig welder for small stuff.. Nah 
I imagine they do exist   

[madScientist]

I understand.
I've looked for a donor carb body but they aren't anywhere available..
I'm seeing that JBWeld makes lots of new products(2-part epoxies)besides their old standard 2-part grey tubes which I'm used to;maybe one of those might work.

I cut the section of the threaded top part off just shy of the inner machined slide bore so the slide won't touch that area.
I took it to my welder this morning and he told me if he tig welded it that the threads might get some damage.
I asked him if he had a tiny little tig welder for small stuff.. Nah 
I imagine they do exist   

It might be worth sending an email to Jim and see if he could work some magic on it.

[grcamna2]

I understand.
I've looked for a donor carb body but they aren't anywhere available..
I'm seeing that JBWeld makes lots of new products(2-part epoxies)besides their old standard 2-part grey tubes which I'm used to;maybe one of those might work.

I cut the section of the threaded top part off just shy of the inner machined slide bore so the slide won't touch that area.
I took it to my welder this morning and he told me if he tig welded it that the threads might get some damage.
I asked him if he had a tiny little tig welder for small stuff.. Nah 
I imagine they do exist   

It might be worth sending an email to Jim and see if he could work some magic on it.

I appreciate it man 
 I use this bike as my daily and I hope a product from JBWeld like 'Tank Weld' ? can work?  I just heard about this from someone..