Topic: Nebraska CB750 K8 Resto/Mod

[zeffcat]

Picked up this 1978 CB750 w/ about 35k miles for $600 last week. It is a non runner project - engine & carbs are not seized, thankfully. Seems to be mostly complete except for the lack of a stock airbox and the awful mufflers that were welded on. The PO also gave me the original seat which is in great condition and may be up for grabs along with the king/queen seat pictured.

Here is the bike at its starting point - untouched by me.


Here is the bike I plan on basing my project off of - from a small motorcycle shop called Catrina Motosurf.


Right now I am doing some electrolysis on the gas tank trying to get the inside cleaned up.

[slikwilli420]

Why the useless knobby tires and skateboard seat? It's less functional than stock and has been done to death. How about some sticky street rubber, reshaped stock seat and some good bars for a bike that is better than stock?

[zeffcat]

I have an appreciation for the gnarly, aggressive look of a scrambler build I guess. I wouldn't go as with such an aggressive tire tread. But I'll admit, I'm still in the consideration phase of what I want to do with the bike. If I don't go with the scrambler-esk look I'm wanting to do exactly what you just said. It would be much simpler and honestly a lot more rideable - especially for longer trips.

I also have this picture in my "ideas" folder basically because I liked the seat.

[slikwilli420]

Second one is stunning and classic. Bob the rear fender a bit and it's a hit.

[Stev-o]

Second one is stunning and classic.

+1.   Look on eBay for that seat. 

[calj737]

Regarding that first picture you posted; someone needs to take it behind the barn and beat the ugly out of that POS for an afternoon.  WTF possesses people to destroy any aspect of performance improvement? I get styling changes, but those tires, seat, exhaust and pods all account for performance downgrades.

If you want a scrambler, buy a scrambler. A real one. But please don’t follow these dolt’s design ideas...

[zeffcat]

I think I may have had a change of heart... maybe . I found this pic and I love the style! Would it be possible to get an 18" x 2.15" rim for the rear and lace that to my hub?

[slikwilli420]

Yes, that would add some much needed ground clearance to the rear. I would also go with stock length shocks to restore the proper steering geometry. The clubman bars are a personal choice and definitely a young-man's bar for longer rides. Other than that, it looks good.

[zeffcat]

Now if I do the 18" rim, do I have to get a special spoke kit from buchanan or will a regular cb750 18" spoke kit for the 69-76 cb750k work?

[zeffcat]

Update on the electrolysis rust removal, been running since Thursday afternoon. I've been cleaning off the sacrificial anode once or twice a day. The picture was from this afternoon after running about 28 hours.

[zeffcat]

Starting tearing into the carbs today, they really aren't too bad. I'm letting some PB Blaster soak into the threads so I can get everything apart then I'll soak the bodies in pine sol and get the jets cleaned up.


There is some rust on the throttle shaft, I can clean that off with a wire wheel but whats the best way to keep it from coming back?


Has anyone used this gasket kit from 4 into 1 that can attest for it? The price is right.

[calj737]

Pine Sol is very acidic and will first turn your carbs grey, then ultimately attack the alloy. Use something else.

[MoMo]

Try simple green purple or krud kutter


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[zeffcat]

Pine Sol is very acidic and will first turn your carbs grey, then ultimately attack the alloy. Use something else.

Hmm, good to know. Thanks. I've seen on various other forums (and I thought this one too) about guys using it and swearing by it.

[calj737]

Pine Sol is very acidic and will first turn your carbs grey, then ultimately attack the alloy. Use something else.

Hmm, good to know. Thanks. I've seen on various other forums (and I thought this one too) about guys using it and swearing by it.

Some do. But some, actually pay attention to chemical compositions and their tendencies. You may have luck and no adverse effects. But you might not because of the time you allow it to soak, temperature, etc. So why risk it? There are too numerous other choices that are safe (MoMo mentioned a great one) to run the risk.

[MauiK3]

I used 50-50 simple green and pure water in my ultrasonic cleaner, worked great with no sign of metal damage. The  ultrasonic cleaners are a great investment for worry free cleaning. I put everything in it that would fit. Did my valve/cam cover half at a time.

[zeffcat]

That's a good point Cal. I've used the purple simple green before for aluminum since it's non-corrosive and liked it so I'll get a other gallon.

Maui, normally I take my carbs to my local shop guy and he would run them through the ultrasonic cleaner for a few bucks. But unfortunately he up and moved towns in the middle of my last build.

Any input on a budget friendly gasket set for the carbs?

[zeffcat]

Few updates:
Tank is pretty well cleaned out. The strainer was stuck up in there, I think it's cheaper to buy a new replacement petcock than take the original apart and replace the seals.


Carbs are nearly done, just haven't had time to put them all together. All I need is to grab some fuel line for the short pieces in between the carbs. Also did a quick polish of the top caps and bowls.


Today I cleaned up the old manifold clamps and shot them with some VHT caliper paint, then baked them to cure.



And finally here is my '81 Yamaha XS1100 project I'm pretty much "done" with.

[zeffcat]

Wanted to make a quick mention of the gasket kit I got from 4into1. It seems to be really great quality and all the o-rings are perfect sized and the float needles are spot on as well (original on top, new on bottom). They were cheap and seem to be great quality!



Also a close up of the original jets cleaned and polished up a bit.

[Restoration Fan]

Really nice work on the carbs.  I highly recommend you keep that original petcock just in case you aren't pleased with the replacement ones for the 78.  I ended up getting an original 78 replacement for mine from Bill Benton because the 2 "new" ones I bought from different suppliers were cheap quality and leaked like a sieve.

[seanbarney41]

Hope you have not thrown out the tubes that go between the carbs.  They contain tiny restrictors that allow the accelerator pump to function.

[zeffcat]

Hope you have not thrown out the tubes that go between the carbs.  They contain tiny restrictors that allow the accelerator pump to function.

Nope I've still got them! Im glad I held onto all the rubber parts, I had no idea they had restrictors in them. I just thought they were regular fuel hose. So can I remove the restrictors and put them in new line? The original lines are pretty stiff.

[zeffcat]

Really nice work on the carbs.  I highly recommend you keep that original petcock just in case you aren't pleased with the replacement ones for the 78.  I ended up getting an original 78 replacement for mine from Bill Benton because the 2 "new" ones I bought from different suppliers were cheap quality and leaked like a sieve.

Okay, maybe I'll reconsider rebuilding it then. I'm trying to keep the costs down with this resto so I'd hate to waste money on a replacement and end up having to rebuild the original anyways.

[zeffcat]

Carbs are more or less done. The accelerator pump fuel lines are soaking in the wintergreen oil mix to get them softened up a bit, verified the restrictors are still in place. Have one stripped bolt hole for a float bowl to take care of still. Got all the stainless socket bolts from boltdepot.com, I would highly recommend them as they are way cheaper ($15 shipped for replacing all exterior bolts) than the hardware store and I placed an order wednesday and received the bolts saturday. Very impressed w/ them.





Drilled the front plate rivets out of the petcock and used a punch to smack the plate off. Found this loveley mess underneath, no wonder it wasn't working correctly. Ordered a new seal from ebay (part #    
16955-268-020) for $7.50 and a new fuel strainer w/ o-ring from 4into1 for $24.



I also checked the compression of cylinders 1 & 4 quick since they are easiest to access and both were about 90 psi - so pretty awful. I'm going to verify valve clearances and timing and see if that helps at all. I wouldn't be surprised if piston rings and or valve seals are shot. So my first engine teardown may be in order. But I'll be sure it needs it before I get too bent out of shape about it.

[calj737]

Don't jump to any premature conclusions from the compression numbers. It is very common for the readings to be low in an eying that has sat for a length of time. Several good run cycles often sees that number recover once the rings get moving again, and de-coked.

Also, if your compression tester is an automotive type with a long hose, that too distorts the reading. More important that all four cylinders read within 10% of each other than the actual number.