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Starting to restore a 1978 CB750F SuperSport

7K views 27 replies 7 participants last post by  WintrSol 
#1 ·
Working on the carbs and gas tank now. All going well. Tires are shot. Any recommendations on replacement tires?

I'm pretty sure I'll go 75 or so, but very sure I'll not try to bust 100. I'm 52, have not ridden in 20 years and care more about safety and handling than durability or high speed performance. Thanks!
 
#2 ·
I've tried Dunlop and Avon tires on both my bikes, and, of the two, I find the handling, especially on wet pavement, much better on the Avon's. Plus, most are available in inch sizes, as called out by Honda on these old bikes. They'll be more than 100, though.
 
#3 · (Edited)
I'm running 120/90-18 rear and 100/90-19 front, whatever brand works for you.\

Edit: In reply to your comment on my resto thread, the rear is a Shinko 712 which is working fine. Oddly, I had an issue with the front so I have an old Continental there now. My next choice for this bike would be a set of Bridgestone S11's.
 
#6 ·
I had a '79 CB750K for six years. Rode on Pirelli MT66 Route tires, only thing I ride on now, with a 1200 touring bike after the Honda's impressive ride with them.

We rode two up, full saddlebags, trunk, and tank bag (bike overloaded...), four days, in the rain, leaning in curves because we needed to make the miles, and we were suffering hypothermia... The Honda was glued to the road. Never a traction issue. The touring bike has done equally well on them.

On our tourer, we have 9,000 miles, and the rear tire is shot. Not a problem as we are willing to pay for the traction, even if the mileage is not the highest. The rear replacement will be around $150 for my big touring bike.

They are rated as tubeless, but they work with tubes just fine. Check the Internet for rider reviews. Cheers!
 
#9 ·
Ok, an update and another request foir info/guidance.

Gas tank done and great, carbs work great, ready to synchronize. Tires mounted and balanced. Oil changed and brake calipers rebuilt. So far all moving along well.

The problems/questions-

1) Brake lines and rear brake cylinder. Brake lines are gummed up. Soaking to clean out, but probably want to replace. Need a good source for lines. Can/should I change to stainless lines? Again, where?

2) Rear brake cylinder a hot mess. Broken parts and rusty as all get out. Hopefully we can get it apart and use a rebuild kit. Anybody have a source for a complete rear master cylinder?

Thanks!
 
#10 ·
If you're looking for something you can just bolt on, eBay is probably your best bet. There is probably a decent used rear MC there somewhere. There are new master cylinders out there, but they may not be a straight bolt on.. cyclexchange.net has some.

IIRC, I got my stainless lines from Z1 Enterprises.

If you have some MIG welding wire around, you might be able to snake that through the brake lines and free them up a bit, but honestly you're better off just replacing them.
 
#12 ·
Took forever to get the rear MC cleaned up and rebuilt. Ive been tooling around since Saturday. Mostly slow stuff around the neighborhood. Getting a feel for how the bike handles (it's heavy!), shifts, brakes, accelerates. Took it out of town a bit and got up to 60-65. Very stable. So far, I'm very happy.

The seat is not very comfortable. I think the padding is shot on driver's seat. Foam on rear of seat seems firmer. What's the best way to re-pad the seat? The original seat cover is in great shape - prefer not to trash it if possible. Thanks!
 
#13 ·
Those were very good bikes in their day imo (knew a guy who had one). Pretty much the last of the very famous single cam 750 fours.

The seat is not very comfortable. I think the padding is shot on driver's seat. Foam on rear of seat seems firmer. What's the best way to re-pad the seat? The original seat cover is in great shape - prefer not to trash it if possible. Thanks!
Well, if you can remove the cover, you might be able to add a inch or so of new foam under the original foam. I've seen this done successfully with dual density foam (IIRC, you couldn't see any evidence of the seat being re-worked).
 
#18 ·
That is a bit low. It depends a lot on how you ride, but stock should be between 40 and 50, maybe even a hair above. My 78 has been really modified pretty far fro stock and gets about 38.

If it hasn't run in a while it might just needs some miles. Rings and cylinder walls will clean themselves up and it may come up a bit. Can you smell gas while it runs? Brakes all releasing completely?
 
#19 ·
Well My first superbike was a 750F supersport. Yes it is supposed to get about 26mpg I thought that was low also, but you have to remember these big bikes were not designed for gas conservation, they were designed for performance. good luck with that.
 
#20 ·
A lot can affect the fuel mileage a motorcycle gets - size of the rider, how it's ridden, etc. One thing about the 78F is that it's geared really low which affects mileage at higher speeds. One change I made to mine was to put a much larger front and much smaller rear sprocket on the bike, which vastly improved my cruise RPM and mileage. (It's more compatible with how I ride, and the bike makes enough power to still go like heck!)

Pull your plugs and see what they look like - that will tell you a lot.
 
#21 ·
Drama update. Simple stuff- Plugs very dark, so mix is rich. Will adjust after I figure out how to fix the F%$#@&ing carb that is draining gas at about a cup a minute.

Was driving to gun show about 30 minutes from home. Stopped to fill up tank and gas started draining onto ground. Finally figured it was coming from a carb drain tube. Did the MPG/tank capacity/leak rate math, topped off and hauled ass home. Made it with about a pint to spare (over the reserve).

Something (float?) is stuck in the wrong position or has a bad leak.
 
#22 ·
Near end of season update........

Still having problems with Carbs/mileage. My bike whisperer thinks there may be a problem with the fuel/air emulsifier tubes. Too much gas getting through?

Question for the Old Honda Carb Wizards -

Should those tubes be clear/clean like a straw or should they be partially blocked? Looks like somebody drilled these out.
 
#23 ·
The emulsifier tubes mix air coming in through jets in the intake ports with fuel coming up from jets in the float bowls. They should be clean, and have several holes along the length for the air to mix. If the ID has been enlarged, propermixing may be compromised. Mixing air with the fuel before it reaches the throat of the carburetor makes for a better atomization of the fuel, and better, smoother fuel delivery.

Make sure the air jets are not blocked by bits of air cleaner or other debris, a commonly overlooked area; also, the mounting tubes of replacement pod filters are often too narrow, keeping the air stream from hitting the intake ports properly.
 
#24 ·
Badger, in your carbs it's more likely that what is worn is the silver needle jets which sit above your emulsion tubes. Those are known to egg a bit with age, and can dramatically affect fuel mileage.
 
#26 ·
Thanks guys. My bike buddy wants me to ask the qustion ina very specific manner-

"on the emulsion tubes, when you look in one end, should you be ablke to see straight through the whole length of it? or is it supposed to be blocked/capped?"

He has read that it is supposed to be blocked/capped. When doing my carbs, he soaked and drilled out the tubes. Wondering if that was a mistake?
 
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