Topic: New member - new project 1975 cb750f super sport resto

[blue_roller]

Hi everyone,

New member in Chicago. I own a 1975 cb750 super sport. It needs a little bit of work. My goal is to make it a well running, well maintained, reliable daily rider.

I bough the bike a few years ago from a buddy for < $600. He told me at the time that it didn't run. I added some water to the battery, charged it, and proved him wrong. After a few short rides of it running rough, I discovered that one of the carbs had come disassembled inside. I opened the float bowl and found some of the little brass parts rolling around in the bottom! Solved that problem and took it for a few rides around town and noticed it was developing a loss of power and was leaking gasoline sometimes.

Around that time, about 3 years ago, I met the woman who is now my fiancée, and, in a separate incident, dropped the bike in a low speed traffic snafu. Time and interest (and money) for the bike sort of fell by the wayside.

Now it's time to give it the attention it deserves! At the moment, my goal is to have a reliable form of transportation. I'm also losing the space where it's stored at the end of October, so I'd like to have it all sorted and road ready by then.

I've diagnosed and begun work on a few of the problems already. The fuel leak seems to be coming from old, worn o-ring seals on the fuel pipe connectors on the carbs. I have a new set of those arriving Saturday. I also have a new petcock to install.

Thanks for reading. I appreciate any and all suggestions and advice.

[blue_roller]

So, I've already run into an unexpected problem. I got new fuel line for the float bowl drains. 1/4 OD x 1/8 ID. Seems to be the same dimensions as the originals. I tried it on the float bowl drain nipple. No problem. Then I tried it on the brass nipple on the side of carb #1 that communicates w/ carb #2. This nipple looks same size as float bowl drain. The original rubber tube didn't need replacing, but curiosity got the best of me. The fit was very tight. When I tried to pull the fuel line off, the brass nipple came out!

The nipple fits back in its spot snugly. I gave it a few light taps and it seems sturdy and airtight. Is this something I'll have to worry about? Does this require a bigger fix?

[Jerry Rxman Griffin aka MuthaF'er]

Nice looking start. Was it originally blue or orange? That's a 76 color.

[blue_roller]

Hey Jerry. I see you're a man who'd know about a '75 cb750F. That is the original color you see. The title says 1975, beyond that I don't know.

[Jerry Rxman Griffin aka MuthaF'er]

Hey Jerry. I see you're a man who'd know about a '75 cb750F. That is the original color you see. The title says 1975, beyond that I don't know.

Whats it show on the VIN tag on the steering neck? 75's were produced until the 1st week of 4/75. What's your serial number begin with? CB750F-1xxx or CB750F-2xxx?

Regardless you have a great bike to start with  You should be fine with the brass nipple as is. 

[blue_roller]

I was just glancing at that VIN today but didn't remember it or snap a pic. I'll take one tomorrow since I'm very curious now.

I'll try running the carb as is. If it needs a fix in the future then so be it.

[blue_roller]

Was wiping some grime off the engine today and noticed something. When it was dropped the alternator cover got bashed and took a bit of a dent. It's pretty minor, but, I'm wondering if there are any safety implications. Is this going to interfere with the working of the alternator, create friction, interfere with the crankshaft, etc. Any experience with this out there?

[GritCity750]

That's a nice looking CB750F1!! I personally think the SuperSports were the best looking of the CB750's. There is a lot of great knowledge (Jerry for one) here on the site, especially when it comes to those sweet SuperSports.

cheers!
Jeff

[Jerry Rxman Griffin aka MuthaF'er]

As long as it's not leaking oil and the rotor is not rubbing the stator coil you should be fine. That is assuming you have the proper alternator output also 

[SOHC4 Cafe Racer Fan]

As long as it's not leaking oil and the rotor is not rubbing the stator coil you should be fine. That is assuming you have the proper alternator output also 

Yep, what he said.

[blue_roller]

Jerry, that VIN is CB 750F 101...  What does that mean? Any other indicators?

Thanks guys for chiming in on the alternator cover. It looks OK to me but this is my first project like this and I want to avoid any safety blind spots. 

Still waiting for the o-rings to arrive so I can reassemble the carbs, get some fuel in her and see how she runs. In the meantime I'm going through some maintenance stuff. Found this interesting little bit. If I'm not mistaken, that is one of the rear brake pads with rotor marks on the BACK of it! The PO was running this for a while with one of the pads in BACKWARDS! Was in correctly when I disassembled for inspection though.

[Stev-o]

As long as it's not leaking oil and the rotor is not rubbing the stator coil you should be fine. That is assuming you have the proper alternator output also 

Yep, what he said.

Agree with these guys but I'd put it on the list for replacement.
A nice used one can be picked up from a member here for a reasonable cost. 

[Jerry Rxman Griffin aka MuthaF'er]

CB750F-1xxx is in fact a '75 VIN. CB750F-2xxx would be a '76.

Looks like you have a 75 with a 76 tank and tail piece or repaint. Identical except for color. Side covers for both years were identical as was most other stuff. There were a few changes during the 4 months of 75 when that model was made. IE the rear master cylinder changed from a nylon reservoir to an all aluminum design near CB750F-1007500 or so.

[blue_roller]

Great News! Re-assembled carbs with new o-rings, poured in new oil, poured in new gas and she runs!! Started on the first push of the button. Idles well.

There is much more work to be done, but I'm calling it a night. Thanks everyone for reading and writing up to this point.

[blue_roller]

OK, so the engine is running but I'm getting sporadic leaking from the carburetors. I've read a few of the threads on that here and I have a few ideas what to do. I want to make an auxiliary fuel tank to make the work easier. I have the plastic container that held the acid for my new battery when I bought it. Would make a perfect aux. tank. Does anyone know if that is fuel resistant?

[Jerry Rxman Griffin aka MuthaF'er]

If it's sulfuric acid resistant then gasoline shouldn't be an issue.

Where are the carbs leaking? Bowl gaskets, overflow tubes, floats sticking ??

[blue_roller]

Jerry, luckily I think I might have been a bit hasty in diagnosing them as "leaking".

The day after I first fueled and ran the bike I came back to it and noticed that the overflow tubes had fuel in them and when I shook them the fuel spilled onto the floor. However, I've been back to the bike a few times since and haven't noticed the fuel leaking any more. I think it's possible that the leaking was just part of the system accepting gasoline for the first time in a long time. I'm going to give it some more observation try to catch it leaking again. In any case, I'll try making that aux. fuel tank. 

I noticed that the front lower brake line is badly cracking near where it meets the metal pipe from the caliper. Payday is tomorrow and I'll be placing an order for new stainless lines.

[firebane]

Fuel lines for these bikes are 5mm not 1/4 which is why it may have made a head scratch moment

Also clean bike.

[riffman12]

nice pickup! I recently finished a restoration / cafe build on a '76F in the same color. Perhaps you'll find some useful info in my thread down the road:

http://forums.sohc4.net/index.php/topic,152046.msg1737815.html#msg1737815


My only concerns with that bashed stator cover would be that it could be causing the wires to ground and short. Easy to test with a multimeter.

[blue_roller]

Thanks Firebane.

Riffman, thanks for linking your thread. There's definitely some info and inspiration in there I can use. That finished bike looks awesome!

Some updates on progress. The front brake line was in very bad shape (see pics). I ordered a kit from Slingshot Cycles to replace all the brake lines in stainless. The new line will eliminate the metal front brake tube. Are there any special issues to be aware of when making this switch?

In preparation for the new line installation I pulled the front MC and caliper for inspection and cleaning. The MC has been oozing fluid onto the lever, so that looks like I'll need a rebuild kit.

Tried to pull the caliper piston for inspection but couldn't get it out. I'll try that again tomorrow w/ compressed air.

So I have noticed that all over the bike there are these dabs of yellow and red paint. What can I learn from these? Was this bike raced/on a track?

[blue_roller]

Been a while since I updated here. Was waiting on parts for a few days and then most of the work was smooth going/not very noteworthy.

Got the MC rebuilt. Installed new stainless brake lines by Slingshot Cycles (eliminating front brake pipe). Re-wired broken rear turn signal. In the process I cleaned up some some really dodgy looking wiring repairs made by PO.

Buttoned everything up yesterday and fired her up. Rough idle. Cyl. 3 not firing, cold exhaust on that cylinder. Tore apart carb #3 and found a fouled pilot jet. Problem solved? This caused me to notice that #3 pilot jet is stamped "38". All the others are stamped "40".     Did I just find a new problem?

Definitely caused a new problem. Couldn't leave a stuck bowl drain well enough alone. Twisted the head of the screw right off.  Used bowl w/ drain screw on order from Ebay.

BTW, Found a nice little tip for making fine work at the workbench cleaner and more enjoyable. I have some waxed butcher paper in the shop and rolled out about 36", taped it to the bench. It gives a totally clean starting work surface, makes seeing the little carburetor parts much easier, and helps to keep crud from the workbench from getting back into the carbs. When it gets cruddy, just tear it off and lay down a new one.

Riding this thing is so close I can taste it! Looks like 1st week of Nov. There's still some riding season left, right? Right??

[blue_roller]

 Got everything buttoned up and took the bike out for a little ride today. So great. Runs well.

I was able to plug the float bowl with the broken plug with some JB Weld "Steel Stick" epoxy putty. That stuff works pretty well and quickly.

Once I have that bowl replaced I think I'm done. Just going to ride for the rest of the season.

[70CB750]

Very good, many safe miles