Topic: 1978 CB750 SuperSport Build

[CB_Jeff]

So, I have had this bike for just about 3 years now and decided that it is time to post a build thread.  The bike is a '78 F3 / SuperSport and I bought it as a non-running rolling basket case that came with two bins of parts associated with the bike or other 750s that the PO had.

The good: on pick-up it was evident that the bike had been stored inside for most, if not all, of its 36 years, the chrome was rust free, the engine seemed to have good compression and the bike had a new set of tires on it (Shinkos - I think).

The bad was that the bike had been cut-up, the back part of the frame had been cut off south of the shock mounts and the wiring harness had been cut as well.  From what I can tell a PO was planning to make a brat out of the bike and was planning to add a frame loop and also simplify the wiring to eliminate the idiot light tree and also the ignition switch.  The stock handlebars had also been cut and reversed and re-welded to make a kind of homemade set of clubman bars.    Once the brat prep. started, the bike was traded and wound up in a garage halfway up a mountain the in Berkshires... that is where I found it.  The unfortunate part of the state the bike was in when I picked it up was that up until ~2012 the bike was a real clean survivor with ~10,000 miles on it sitting in the second owners garage.

So, despite the disassembled and chopped nature of the bike, I did pony-up $400. for it and brought it home to New Hampshire.  Here are some picks of what it looked like when I picked it up.











The project plan, reconstruct the bike, get it somewhat into in stock-ish configuration, get it running, sort out the brakes and electrics and make some reasonable performance and chassis modifications along the way to make it a bit more compliant.  The stock seat and sidecovers were missing from the bike when I picked it up along with the whole rear fender, grab bar, glove box, tail / brake and turn signal assembly.  I am planning to ditch the whole stock seat and rear assembly for something lighter, likely Airtech Streamlinings CB750f seat / tail section all mounts for the stock seat were ground off, so that decision was an easy one.

Stay tuned for updates.

[70CB750]

Folowing

You dont have to stick with 78F frame, see my signature. The Red is K3 frame with most of the goodies used from 78 SS.

[SOHC4 Cafe Racer Fan]

Great find.  I'd get it running and inspect (rebuild as needed) all of the systems (brakes, suspension, charging, fueling/carburetors) before you need to make design choices. 

You have a lot of options to go with.  If you want a stock bike, buy an 78F frame and swap over all of your parts, and buy a seat.  Not much to do there.  Or use it as the base for a custom.  Having a running bike in good working and safe order is key.  For $400, you stole that bike.

[seanbarney41]

very cool project...it will be great to see us get one back!  I love the f2/3s

[CB_Jeff]

.... and the inside of the tank was squeaky clean.  The outside of the tank was pretty straight but had a couple of nicks and dings.

Here are a couple of additional pics of the back of the frame that I took when I got the bike home.  In the PO's defense, some nice clean cuts, including the plastic inner fender.





So, here are my near term plans:

Tier I: - Get the bike running:

 - Repair the wiring harness to stock, when I brought the bike home I took a good look harness and other than the portion that was cut, the harness looked clean and corrosion free.  I bought a used harness from Whiteorbs that had a good sub-harness section that I needed, so I cut that off the donor harness and grafted it into the new harness.

 - Carb rebuild by Anders.

 - New battery, plugs, filters (air and oil), and oil.

 - New cables... as the other ones looked a bit tatty and had some drag between the casing and cable, I have had the push cable fail while out on a ride, so new cables has become one of my standard upgrades on a new to me bike.

 Tier II: Get the bike ready for road testing, specifically repair or replace the 36 year old parts that are susceptible to poor maintenance and could possibly fail when spun at a couple hundred or a couple thousand RPMs:

 - Wheel bearings

 - 530 Chain Conversion (17T up front and 48 in the back) - JT Sprockets chain and 530 X-ring chain.

- Brakes - Caliper Rebuild (x3), MC Rebuild (x2) and new brake lines, banjo bolts and copper crush washers by Sean and Slingshot cycles, no point on putting any old stuff back on.

Tier's III (frame and chassis), IV (performance upgrades and mods) and V (paint and upholstery) are still a ways out.

[palepainter]

You certainly have a great platform for a build... And at that price!!  Congrats on the score.  I look forward to following a long.

[SOHC4 Cafe Racer Fan]

Solid plan!

[CB_Jeff]

Some updates:

 - The wiring harness repair / splice is complete, lots of 3M heat shrink butt connectors with additional heat shrink to cover the connection, everything including the ignition switch now works.

- Had the carbs electrosonic cleaned and rebuilt by Anders, mounted them up along with the stock air box and the new cables, and

 - As part of cleaning-up the wiring, I pulled off the handlebars that the PO had cut and re-welded, and swapped them out for a set of Eurobars.... which are good for now and some initial shakedown riding. 

Here are some pics:

 





Up next, wheel bearings, some gas and a battery and try to start it up.

[SOHC4 Cafe Racer Fan]

Looking good, as is the original tank, too.

[CB_Jeff]

A quick update on the F3.  As mentioned on my last post, I had the carbs cleaned and rebuilt and also repaired the portion of the wiring harness that had been cut to remove the ignition switch / neutral light / high beam light / oil light sub-harness.  Following that I rinsed out the tank with a bit of fresh gas and some two stoke oil, hooked up a battery, added some fresh gas, hooked up the fuel lines and hit the ignition switch.  The bike did turn over, however it ran real rough and would not get on an idle.... almost like it was only hitting on only two cylinders.  I shut it off, disconnected the fuel lines, removed the tank and started to take a look at the harness, coils and plug wires.

As it turned out, the PO's attempts to modify the harness were not limited to ignition switch, for whatever reason the lead to the right side coil had been cut and then very loosely re-connected, so the bike was, in-fact, only hitting on two cylinders.  The good news is that following a proper repair to that lead the bike fired right up, idled properly and did not smoke.  The bad news is that following a brief period of idle time with a fan cooling the engine it became apparent that the pucks were weeping oil.  As it was more of a weep than a leak, my plan it to hold off on pulling the motor until I have the opportunity to get all the other systems online and tested and then road test the bike.

Up next, wheel bearings, 530 chain conversion and brakes.

Happy 2017 to all!

[CB_Jeff]

.... and now for something completely different...

Now that the bike is up and running and the wiring is sorted out, I decided to put the frame back to stock.  I was able to source a donor F3 frame section from forum member Old Scrambler who took it off his salt flat racer when he lowered the seat.  I decided not to deal with trying to put stock seat mounts back on the frame, but wanted to use the Airtech Streamlining CB75022 fiberglass seat pan and decided the best way to do that was to put the frame back to stock.  Plus, while I am not a purist, I do like the option of being able to put the bike back to stock should need arise in the future.  So here are some pics.  My painter is also a skilled welder and I was able to take advantage of a break in his schedule.

Before:



After:



Primer:



Paint:



Done

[seanbarney41]

great choice for a great job   In 10 years (or less) think how many brat bikes are gonna have to get this treatment when that stupid fad is no longer fashionable.

[700504]

great choice for a great job   In 10 years (or less) think how many brat bikes are gonna have to get this treatment when that stupid fad is no longer fashionable.

For real, sacrificing comfort for looks

[palepainter]

Looks great. I have a few factory parts for the rear on the bike.  Hand rail and rear tail section.  Seat pan from 76 F model.

[CB_Jeff]

Thanks all, while the Airtech CB75022 fiberglass seat that I am planning to use isn't exactly the most comfortable option, I could run a stock set-up if the need arose.
Please see an update below with the fiberglass pan mocked-up.  I mounted it using a set of Frankie's 3/8" mounting blocks which I was disappointed to hear he was no longer making.... they are a very tidy solution for mounting a fiberglass pan without having to drill, fab. brakets, weld, etc....
Also included in this update are:
 - The new wheel bearings were installed (All Balls),
 - Had the tires balanced while they were off for the bearings,
 - Cleaned up the Comstars.... they had some surface rust on them which cleaned-up quite nicely with some super fine steel wool and Meguiars Scratch X compound,
 - I sent the rotors (x3) out to Anubis and had them resurfaced and drilled,
 - A set of Slingshot Cycles brake lines,
 - New JT Sprockets Rear 48T sprocket for a 530 chain, and
 - Picked up a set of rebuilt and powder coated (bronze color) calipers, great deal, saved me a lot of work and I do like the bronze color... wasn't so sure that I would.

 



Oh, I also rebuilt the front and rear Master Cylinders.... which was more work than I had anticipated, it also turned out that I had the smaller 14mm K7 / K8 front master cylinder and not the larger (17 mm) F2 / F3 MC.

The smaller MC seems to get the job done, but I have the parts for a rebuild on the other larger MC when I get to it.

I did note that following bleeding the front system that the action on the left caliper is not as smooth as the right caliper, there appears to be no adjustment on the calipers, I will figure it out.  The back brakes caliper work great!

I also polished up the tank as well as the chrome, which turned out nice.

Stay tuned for more....

[palepainter]

Fantastic.  Are you going to paint the tail section to match the tank?  Really shaping up.

[CB_Jeff]

Thanks!
Yep, I will be painting the tail to match as well as a set of new (from Frankenbike) side covers.  The tank is going to need a bit of touching up as well as it looks like a 2 x 4 or can of paint fell on the right side of the tank and put what my painter referred to an "eyebrow" dent right on the complex curve that comes down from the filler area.  FYI if anyone is interested, the modern base coat / clear coat equivalent for the this red is DuPont's Merlot Red, I had it scanned in at the local Sanel shop, I will post the color code later for those who may be interested.

[SOHC4 Cafe Racer Fan]

Thanks all, while the Airtech CB75022 fiberglass seat that I am planning to use isn't exactly the most comfortable option, I could run a stock set-up if the need arose.
Please see an update below with the fiberglass pan mocked-up.  I mounted it using a set of Frankie's 3/8" mounting blocks which I was disappointed to hear he was no longer making.... they are a very tidy solution for mounting a fiberglass pan without having to drill, fab. brakets, weld, etc....
Also included in this update are:
 - The new wheel bearings were installed (All Balls),
 - Had the tires balanced while they were off for the bearings,
 - Cleaned up the Comstars.... they had some surface rust on them which cleaned-up quite nicely with some super fine steel wool and Meguiars Scratch X compound,
 - I sent the rotors (x3) out to Anubis and had them resurfaced and drilled,
 - A set of Slingshot Cycles brake lines,
 - New JT Sprockets Rear 48T sprocket for a 530 chain, and
 - Picked up a set of rebuilt and powder coated (bronze color) calipers, great deal, saved me a lot of work and I do like the bronze color... wasn't so sure that I would.

 



Oh, I also rebuilt the front and rear Master Cylinders.... which was more work than I had anticipated, it also turned out that I had the smaller 14mm K7 / K8 front master cylinder and not the larger (17 mm) F2 / F3 MC.

The smaller MC seems to get the job done, but I have the parts for a rebuild on the other larger MC when I get to it.

I did note that following bleeding the front system that the action on the left caliper is not as smooth as the right caliper, there appears to be no adjustment on the calipers, I will figure it out.  The back brakes caliper work great!

I also polished up the tank as well as the chrome, which turned out nice.

Stay tuned for more....

Are you going to stick with handlebars or switch to clip-ons? If you stay with bars, the seat should be plenty comfortable assuming you get a decent pad under your backside.

[knippler]

Thanks all, while the Airtech CB75022 fiberglass seat that I am planning to use isn't exactly the most comfortable option, I could run a stock set-up if the need arose.
Please see an update below with the fiberglass pan mocked-up.  I mounted it using a set of Frankie's 3/8" mounting blocks which I was disappointed to hear he was no longer making.... they are a very tidy solution for mounting a fiberglass pan without having to drill, fab. brakets, weld, etc....
Also included in this update are:
 - The new wheel bearings were installed (All Balls),
 - Had the tires balanced while they were off for the bearings,
 - Cleaned up the Comstars.... they had some surface rust on them which cleaned-up quite nicely with some super fine steel wool and Meguiars Scratch X compound,
 - I sent the rotors (x3) out to Anubis and had them resurfaced and drilled,
 - A set of Slingshot Cycles brake lines,
 - New JT Sprockets Rear 48T sprocket for a 530 chain, and
 - Picked up a set of rebuilt and powder coated (bronze color) calipers, great deal, saved me a lot of work and I do like the bronze color... wasn't so sure that I would.

 



Oh, I also rebuilt the front and rear Master Cylinders.... which was more work than I had anticipated, it also turned out that I had the smaller 14mm K7 / K8 front master cylinder and not the larger (17 mm) F2 / F3 MC.

The smaller MC seems to get the job done, but I have the parts for a rebuild on the other larger MC when I get to it.

I did note that following bleeding the front system that the action on the left caliper is not as smooth as the right caliper, there appears to be no adjustment on the calipers, I will figure it out.  The back brakes caliper work great!

I also polished up the tank as well as the chrome, which turned out nice.

Stay tuned for more....

Jeff, bike looks great! I'm planning on getting the Airtech CB75022 as well. How did it work out for you? Any close up shots of mounting that you're willing to share?

Thanks,

Rob

[CB_Jeff]

Right now I have a set of Eurobars on it, which I kind of like, although I may go a bit lower with a set of Superbike or Daytona bars, I am on the tall side, so I don't think that I can do clip-ons and still be comfortable.  The nice thing with the Eurobars is that I can (spoiler alert) run Napoleon Bar End Mirrors and still be able to see out of them.... which is kind of nice.  I have also started hearing about Renthal street bars; being a former dual sport rider from my California days, I have always liked the Renthal gear, top quality.

Knippler, will do on some pics of the seat mounting for the CB75022 pan, top quality and super customer service, although you will need to account for some lead time as my pan took about 6 weeks to get, everyone is hand made as they are ordered.  They have a front lip which installs snugly under the tank and then you can also drill holes in the back to match the rear frame horns... and that pretty much keeps it in one place.  I will get some pics as I have added Frankie's mounting blocks to the equation, but I don't think they are still in production (unfortunately).

[knippler]

Right now I have a set of Eurobars on it, which I kind of like, although I may go a bit lower with a set of Superbike or Daytona bars, I am on the tall side, so I don't think that I can do clip-ons and still be comfortable.  The nice thing with the Eurobars is that I can (spoiler alert) run Napoleon Bar End Mirrors and still be able to see out of them.... which is kind of nice.  I have also started hearing about Renthal street bars; being a former dual sport rider from my California days, I have always liked the Renthal gear, top quality.

Knippler, will do on some pics of the seat mounting for the CB75022 pan, top quality and super customer service, although you will need to account for some lead time as my pan took about 6 weeks to get, everyone is hand made as they are ordered.  They have a front lip which installs snugly under the tank and then you can also drill holes in the back to match the rear frame horns... and that pretty much keeps it in one place.  I will get some pics as I have added Frankie's mounting blocks to the equation, but I don't think they are still in production (unfortunately).

Thanks Jeff! Do you plan on fabbing up a pan to put underneath or are you going to leave it open?

[CB_Jeff]

I am going to use the CB750 upholstery pan to go on top of the fiberglass pan, but nothing planned for between the pan and the frame.  The fiberglass pan is pretty stout, and should be strong enough w/o reinforcement.  Also with the front section of the pan mounting under the tank the pan will need to sit on the frame or very close to it.

[knippler]

Sounds good Jeff, thanks for the info!

[kap384@telus.net]

Looking good

[WesTenRacing]

Great find.  Man you did a nice job of cleaning and polishing it up.  It looks great.  Following along.