Author Topic: Nebraska CB750 K8 Resto/Mod  (Read 17188 times)

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #75 on: April 12, 2018, 12:15:13 AM »
I considered PJ1 as well but I've had good luck with VHT and it's readily available locally, also was on sale 2 for $12 so that's a plus. Went the extra few steps with this to ensure the best paint adhesion I could. Forgot to mention that it was silica blasted beforehand too.

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #76 on: July 18, 2018, 12:53:22 PM »
Finally made some progress worth noting. The engine has been reassembled and oil pressure checked so I went ahead and put it back in the frame last night.





Wheels are also reassembled and waiting to be trued up and have tires installed.

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #77 on: July 19, 2018, 07:22:11 AM »
Realized last night I forgot to put the tach drive gear in the valve cover before reinstalling the engine :-X. So looks like I'll be pulling the engine back out to get that back in.
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Offline SOHC4 Cafe Racer Fan

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #78 on: July 19, 2018, 08:42:20 AM »
Realized last night I forgot to put the tach drive gear in the valve cover before reinstalling the engine :-X. So looks like I'll be pulling the engine back out to get that back in.

Bummer.  I feel your pain.  This is yet another argument for a frame kit.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #79 on: July 19, 2018, 09:03:59 AM »



Bummer.  I feel your pain.  This is yet another argument for a frame kit.

Really wishing I would have jumped for that before powder coating the frame.



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Offline Jnel

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #80 on: July 19, 2018, 09:32:49 AM »
Do it now.  It makes the job so easy.  Best investment I made on my mod.

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Offline SOHC4 Cafe Racer Fan

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #81 on: July 19, 2018, 10:19:36 AM »



Bummer.  I feel your pain.  This is yet another argument for a frame kit.

Really wishing I would have jumped for that before powder coating the frame.



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Use Frank's no-weld kit.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline calj737

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #82 on: July 19, 2018, 10:37:35 AM »
You can probably fish it in and get it to synch if you rotate the motor gently and slowly. You might get lucky... Beats yanking the motor.
'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #83 on: July 19, 2018, 10:46:58 AM »
You can probably fish it in and get it to synch if you rotate the motor gently and slowly. You might get lucky... Beats yanking the motor.
Only problem is the retaining bolt.

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #84 on: July 20, 2018, 11:01:41 AM »
Got the tach drive gear in and the engine mounted back in the frame.  8)
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #85 on: July 27, 2018, 03:09:44 PM »
Standing on her own again, perfect timing for moving to a different state next week. Found the right side spacer for the rear wheel was incorrect (20mm instead of a 35mm) so I'm tracking one of those down. Also think my handlebar clamps got misplaced at the powder coater's since they aren't in any of my boxes so I'll need replacements for those.



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« Last Edit: August 27, 2018, 07:40:51 PM by zeffcat »
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #86 on: August 27, 2018, 07:39:44 PM »
Got the bike running this past weekend! Carbs need balanced yet and it stalled when slight throttle was applied. Found the accelerator pump system malfunctioning. The retaining plug in the cap that holds the check ball and spring in place was missing and the check ball was seized. Got it freed up and fabbed up a new retainer from a nylon machine screw. Accelerator pump now functioning correctly. In case you lose the check ball, its ~3.1mm and could probably be replaced with a ball bearing.

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #87 on: September 05, 2018, 04:56:15 PM »
I've been diagnosing a poor idle condition and think I've finally found the culprit.

Coil 1&4 values:
- Primary winding: resistance = 4.6 ohm
- Secondary winding: resistance = ~12k ohm

Coil 2&3 values:
- Primary winding: resistance = 1.6 ohm
- Secondary winding: resistance = ~12k ohm

All plug caps ~5k ohm



« Last Edit: September 06, 2018, 08:30:49 AM by zeffcat »
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #88 on: September 11, 2018, 08:18:41 AM »
Picked up a set of stock coils that tested well for $10. Wires were short and stiff so I replaced them and took some pictures along the way.

This dremel tool makes quick work of the job.


Shoot for removing about this much material from the longer side, the rear (deeper) portion you want to leave ~3/4" to avoid damaging where the whire attaches. Then snip the wire flush with the coil and use a pick or something to pry out the wire. After its out, strip the jacket off leaving the wire exposed, trim to ~1/2". 




"Tin" the old and new wire, autozone or advanced auto parts sells a 60%/40% (lead/tin) solder that works really well. Minimize the amount of time with heat on the old wire. Slip the new wire in (~1.5' section of 7mm copper core), I used aerosol silicone lube to make this easy. Heat solder to attach wires together. This picture also shows the shorter side exposed and jacket stripped, be extra careful not to go too far back on the shorter side with the dremel tool.


Both sides soldered in.


To seal I used permatex "the right stuff". Squirt it around, focussing on the exposed wire. Let it set up for 15 minutes or so till it is like a playdough then push it down with your finger to make sure it gets all the way under the wire to form a waterproof plug. Add more at this point if needed.


After the gasket material set up for a couple hours (probably wise to wait 24hr) I applied 2 part epoxy (I used gorilla glue clear epoxy - $5 at walmart). I didn't use anything to support the epoxy, such as tape, but that may be helpful to keep it from running down the side.


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Offline RAFster122s

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #89 on: September 11, 2018, 09:22:41 AM »
Nice demo, short and to the point. Are you leaving the wires a little long for future trimming of the cap ends? Did Advance Auto have copper core plug wire or did you source it another place?  How expensive was the wire a foot?
« Last Edit: September 11, 2018, 09:24:37 AM by RAF122S »
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #90 on: September 11, 2018, 09:41:09 AM »
Nice demo, short and to the point. Are you leaving the wires a little long for future trimming of the cap ends? Did Advance Auto have copper core plug wire or did you source it another place?  How expensive was the wire a foot?

Yes I did make sure to have a little extra for future trimming. Advanced auto did not have copper core but O'reilly's did have tinned copper core. I ended up getting mine from another local automotive parts store but it was also tinned, which should be just fine. I paid $0.59/foot. Pretty cheap. If you have to order it, you can find it on ebay for $1-2/foot.
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #91 on: September 19, 2018, 03:44:53 PM »
The bike is idling but clearly running lean - backfiring/popping through carb (throughout throttle range) even with fuel screws at max turns out. Engine bored over 1st size (61.25mm), stock air box, MAC 4-1 exhaust. #35 pilots, #110 mains. Going up to #40 pilots (#38 was unavailable), and #115 mains and will see if that gets me running better.

Some good info for PD carbs in this thread.

I have verified every other possible avenue for poor idle conditions: timing w/ strobe light, point gap .014" and both dwell at 26 degrees, valve clearances at .05" intake and .08" exhaust, spark plugs new and gapped to .6mm, stock coils with fresh wires (primary 5ohm; secondary ~15k ohm), blue spark on all 4,  float level 3mm below gasket (running condition), accelerator pump functioning well, pilot jets pulled and cleaned along with all other jets (whole carbs dissaembled)
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #92 on: September 25, 2018, 01:23:20 PM »
Got the new jets in and boy it made a world of a difference! Great throttle response now, need to do a plug chop to see how it behaves on the road. So my set up is as follows (sea level at my location):

115 mains
40 pilots (overkill - 38s would be perfect)
stock needle
.75 turn out on fuel mixture screw
14.5mm float height

MAC 4-1 exhaust
Stock airbox
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #93 on: September 30, 2018, 10:26:30 AM »
Here she is as she stands now. Going to paint a deep metallic green (I think), don't know when I'll be able to get around to that though. I also plan to change the bars, I like the height but the angle back puts my wrists in an uncomfortable position. At some point I may bob the rear fender a bit and go with a more sleek taillight and also less bulky turn signals.

Still working on fine tuning the carbs. I'm too rich with the 40 pilots, from a cold start with the choke on it doesn't allow the idle to raise correctly (bogs down quickly) and yes the fast idle has been properly set. After its warmed up completely it idles beautifully. I have noticed theres a spot about 1/4 to 1/2 throttle (2nd gear, ~3.5k to 4k RPM, 35-40mph) where it almost stumbles but its very hard to notice. I can feel the bike almost lag but not strongly. I'm thinking thats due to the rich pilot circuit. Once 38s for the pilots are available I'll toss those in and see how it acts.



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Offline 754

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #94 on: September 30, 2018, 12:37:27 PM »
 Got a big vise ?
 Get  2 2x8 pieces, set The bars between them up to about an inch below the top bends. Now clamp in vise,  or bolt to an immovable object . Now sip a forktube or pipe over your bars, padding wont hurt  .. now bend to the angle desired.
 You can probably do it with the wires in the bars (different years have that )
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #95 on: October 08, 2018, 05:47:44 PM »
Another "The Works" toilet bowl cleaner success story for gas tank rust removal! My process was pretty simple:
1. rinse tank with water to remove loose material
2. added 6 containers of toilet bowl cleaner
    - make sure its not "the works basic toilet bowl cleaner" but instead just "the works toilet bowl cleaner". The "basic" works but not
      nearly as fast.
3. after seeing clean metal all around the tank, rinse thoroughly with water
4. add 3 gallons of water with 4 tablespoons of baking soda to neutralize the acid
5. rinse thoroughly once more and remove as much of the water as possible
6. add a quart of acetone and shake all around the tank for several minutes
7. drain as much acetone out as possible and heat with heat gun until no liquid is heard or seen
8. quickly fill with gasoline

I didn't have a problem with flash rusting using this method even with the 70% humidity we had here today.

Before



After

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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #96 on: October 15, 2018, 03:57:07 AM »
I seem to be getting a bit of oil foiling on my #4 spark plug, the rest are getting closer to being tuned in correctly. I only have about 100 miles on the rebuild and haven't ridden it real hard yet. I'ts a bear to start but once I get her going she is beautiful, excellent throttle response in every gear till redline so I think I'm close on tuning. Should I be concerned about that oil foiling yet or am I still safe and just need to ride it real hard to get the rings to bed in?
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #97 on: January 22, 2019, 06:20:49 AM »
Several updates on this project. Over my winter break from school I finally figured out my tuning problems. I added 2 mikuni needle shims under each needle and my mixture screws are set at about 1.25 turns out for 1 & 4 and 1.5 turns on 2 & 3. Spark plugs are all nice tan color now consistently. Also had to fix a bummed thread on spark plug hole #3 and got a back tap thread tool to do the job, it make quick easy work.

The paint is finally finished and I'm happy with the results. Emblems have been repainted with gold lettering and black background, just need to get them back on.



Changed to lower euro bend bars, shortened up the clutch cable to fit properly.

Wheels are off and I'm getting them all trued and torqued properly thanks to a harbor freight wheel balancing stand.

Rear shocks need replaced, they are leaking oil all over my rear wheel and swingarm. I found a set of replicas on Niche Cycle Supply here.

Exhaust is ugly and the headers are rusting. Thinking about replacing with a stainless set from delkavic.
« Last Edit: January 22, 2019, 06:24:26 AM by zeffcat »
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Offline zeffcat

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Re: Nebraska CB750 K8 Resto/Mod
« Reply #98 on: January 23, 2019, 05:13:51 AM »
Was able to get the rear wheel trued very well, I'm quite happy with the result.

Clip of vertical true
Clip of horizontal true

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