Author Topic: Pin2Hot's 73 CB750  (Read 56284 times)

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Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #300 on: April 15, 2022, 06:37:18 AM »
Been an exciting and satisfying week seeing a lot of things come together on the bike.  I finally got around to doing the "easy" stuff that I'd been putting off which in reality wasn't as easy as I'd hoped.  But all the more satifsying to get it done. 

Last night I welded on the rear brake linkage arm to the donor 929 brake lever.  This was actually my second attempt at doing this and I got a lot smarter about making my assembly more solid and pre-heated it a TON before lighting it up.  The pre-heat really allowed the weld pool to form where I wanted it instead of all the heat going into the arm and melting it before getting a good tack in place.  It's definitely not pretty but it ain't going anywhere.

Arm tacked in place:


Welded up ("pretty" side):


Full linkage set up:


Back view:


The hardware used here is temporary and I'll replace it with nice new stainless nuts/bolts but it functions perfectly and I couldn't be happier.  One last important thing to do will be to add a return spring and stop adjuster for the pedal.  Right now it's relying on the drum brake return spring to disengage the brake which will work but I'd rather have a hard stop and additional spring for added safety.  I'm hoping this will be a simple thing but who knows.  I have a plan for it and will work on that next.

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Re: Pin2Hot's 73 CB750
« Reply #301 on: April 15, 2022, 08:15:39 AM »
*Like*   ;)

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #302 on: May 03, 2022, 12:04:20 PM »
Ok after fighting with these studs I've finally gotten things sorted out.  I bought some 12mm round stock and had 8 new studs machined at a local machinist.  Thank you to Tom at M & H Machine Inc. in St. Louis for helping me out.  He also machined down the Cognito Moto spacer to get the proper adjustment I was looking for.

Couple lessons learned: try and give your machinist a drawing in his native language.  I'm a proponent of the metric system and this being a metric bike, I provided a drawing for him in millimeters.  I discovered he quickly wrote in what that means in thousandths...  The other lesson is if you provide a die for your machinist, specifically a split style die, make sure he knows you've adjusted it AND provide a nut for him to test the threads with.  I did neither and it cost me an extra $30 for him to redo the threads with the proper die adjustment. 

All that being said, I have 8 very expensive studs and a properly fitting spacer.  I'm glad I had him make 8 because I trashed 2 in the process of inserting them.  Inserting them ended up being almost as complicated as getting them out.

New vs old studs:


I chased each hole with a M12 x 1.25 tap:


I locked up two nuts above the last thread on the upper threaded section so I could turn the stud into the hole.  This was tricky because the first time I ran a nut all the way down and cranked down on the stud to the bottom.  But trying to get the nut off the thread proved to be impossible without backing out the stud.  It takes a LOT of force to get those studs down there but apparently MORE force to undo a nut that's been jammed onto it.

All four studs:


New, thinner spacer:


All assembled (will bend all the tabs in when I'm 100% ready)


I received my low beam bracket from Osh Cut last week so the next step is getting the low beam mounted and the wiring finished.  My new tank sealing kit arrives this week as well so I'm hoping to have this thing fired up sooner rather than later.  Pretty sure I've said that before . . . .

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #303 on: May 04, 2022, 06:52:02 AM »
Lots of progress this week, feels very good.  I got the rear wheel all set up last night and things look nice and straight.  I'll probably invest in a small chain alignment tool just to ensure I'm tracking completely straight.  I spent some time getting the low beam bracket mounted to the headlight plate which is a huge milestone.  This means I can now finally mount the headlights and get the entire front end wired up.  That leaves just a small number of electrical items to complete before I can put a bow on the electrical system.

Straight AF:


Low beam bracket before removing the material necessary for the bending process.  I was smart this time and had them laser cut the mounting holes for me which made locating the corresponding holes on the plate a lot easier:


I have yet to drill the upper holes for each headlight, that will be done when I'm aiming the headlights.




Tank sealer should be here soon and a 4into1 order is on the way too with new oil filters and a new gas cap.  Hoping to tackle the inside of the tank to be able to get riding.

Offline MauiK3

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Re: Pin2Hot's 73 CB750
« Reply #304 on: May 04, 2022, 08:05:06 AM »
Lots of nice fabrication there!
1973 CB 750 K3
10/72 build Z1 Kawasaki

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #305 on: May 05, 2022, 06:44:29 AM »
Lots of nice fabrication there!

Hey thanks!

Spent some more time last night mounting the lights to get a real feel for how they look, gotta say I'm very pleased with it.  It's funny to look back at the old paper drawing I hung on the front of the bike way back when and compare it to the actual design:

Waybackwhen:


Actual:


Close-up:


Lit-up:


And just a nice overall view of the bike:


Next items are sealing the tank, finish the wiring, put the oil lines back on and fully mounting the headlight bracket.  I have all the parts necessary for this and hope to work on this a lot this coming weekend.  Exciting stuff.


Offline SOHC4 Cafe Racer Fan

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Re: Pin2Hot's 73 CB750
« Reply #306 on: May 05, 2022, 08:17:48 AM »
Looking good, Kevin.
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 Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #307 on: May 20, 2022, 05:47:10 AM »
Been working on wiring up the front of the bike since mounting the headlights.  Because a lot depended on getting those lights put in place, I've been able to finish up a lot of the "little" stuff I've been putting off . . . seems to be a common theme here.  As usual, the little stuff always takes longer than you think.  The first hurdle was trying to remember how I designed the circuit board so I could put the pins in the right connector positions.  I thought I'd messed the accent / turn signal wiring up like a hundred times because I kept interpreting the PCB different ways but fortunately I got it right.  Good thing too because I literally have one crimp pin left, didn't leave much room for error.

Once everything was wired I temporarily put power to it all and was happy to see everything worked as designed.  A note about the low beam: since I'm using an off road ultra high power light for my low beam, I'm using a power resistor in series with it to dim it when operating as my normal low beam.  That required a dedicated relay on the PCB to switch the resistor in and out of the circuit based on the position of the high beam switch.  Baja Designs actually offers a low power harness for my particular light which is literally just a resistor in series.  I bought the same resistor from Digikey and mounted it to the aluminum headlight plate which serves as a monster heat sink to help dissipate a lot of the heat generated when in operation.  When testing off-bike, it was getting pretty toasty but now it's just barely warm to the touch when operating. 

Accent lights working:


Wiring of the accent and turn signal LED strips. (Four cables with zip ties in the top right).  You can see the low beam relay as well, bottom left.


I was particularly proud of how the resistor was mounted.  I had to grind down some M3 hex button screws to clear the resistor body and drilled/tapped the plate to accept them.  Makes a great thermal connection to the plate so I'm not worried about overheating anything.  Don't mind the previous attempt above with the large hole and snapped off screw . . .


Location of the resistor.  It's all wired in now and fully functional.  In the image above showing the wiring of the accent / turn signals, you can see two open holes in the PCB, that's where the resistor wires in.


I shot a video of the light functioning but because it's less than a minute, YouTube turned it into a Short which means I can't post it sooooo thanks YouTube.  Once I finish all the wiring I'll post a video of everything functioning.


Offline RAFster122s

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Re: Pin2Hot's 73 CB750
« Reply #308 on: May 20, 2022, 06:02:56 AM »
Nice...
Tidy work. Thanks for the update...
Enjoy the fruits of your labor!
David- back in the desert SW!

Offline SOHC4 Cafe Racer Fan

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Re: Pin2Hot's 73 CB750
« Reply #309 on: May 20, 2022, 07:58:50 AM »
Very clean work!
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 Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #310 on: May 20, 2022, 08:09:23 AM »
Nice...
Tidy work. Thanks for the update...
Enjoy the fruits of your labor!
Very clean work!

Thanks guys.  If only my workbench were clean and tidy.

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #311 on: May 24, 2022, 09:02:52 AM »
Getting very close to bringing this bike back to life.  Only a few more wires to terminate and tidy up and I'm ready for mechanical action.

This bike hasn't been fired up in almost 4 years so I'm going through the list of actions to take prior to adding spark:
    -Bench sync carbs again
    -Maybe put some Marvel Mystery in the cylinders just prior to priming, thoughts?
    -Prime oil system, change out filter after priming

Fire it up!
    -Sync carbs

Need to get some copper washers for the front brake and then I'll get brake bled and tested, rear works fine.

I took a video of the electrical system again to show the function of the front plate.  It's kinda funny looking back at my original video showing its function and comparing it to now.  I'm crazy happy with how it turned out, I think it'll look really good going down the road.



Offline Shtonecb500

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Re: Pin2Hot's 73 CB750
« Reply #312 on: May 28, 2022, 08:52:25 PM »
looks good man, the hard work will pay off.
73/74'' CB500/550 resto-mod - sold
75' 750f 91' cbr f2 swap cafe - mock up
74' 750 chopper hardtail - complete - sold
74' CB750/836kit - Black mix & match - daily rider - always tweaking
71' cb500 K0 survivor - complete
71' K1 - CANDY GOLD/BROWN Winton kit - in process

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #313 on: May 31, 2022, 06:55:45 AM »
It lives once again.  Spent the end of last week on some final electrical items and tidied up a few connections.  I also got oil flowing through the engine again and fired it up.  Check out the link below, friggin YouTube and their Shorts videos....

https://youtube.com/shorts/gIYko1WSQUU?feature=share

I noticed a pretty lumpy sound at first and noticed cylinders 1 and 4 not nearly as hot as 2/3.  It evened out as I would rev but it doesn't appear to be firing equally all the time.  Spent a lot of time digging through some threads on a similar issue and everything points to carbs.  I need to take them off the bike anyway to install the sync tubes (it's easier in my opinion) so I'll double check my slow jets aren't clogged and all match one another.  I'll do the same for the fast jets.

I actually checked compression last night (cold, wide open throttle, starter motor) and got similar results across 3 cylinders with #2 being the lowest and not within 10%. 

1: 132
2: 122
3: 130
4: 140

Not sure what's up there, all cylinders have new rings and pistons.  I'll do a warm check later this week to see if things change.

Any 3rd party opinions judging from the exhaust note?  Very happy to have it to this point, looking forward to syncing the carbs and getting it to run more smoothly.  I also anticipate some other weird issues as I start to ride it which is wild to even say out loud here considering it's been 14 years since I bought this thing.  BUT, soon, I'll be riding it.

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #314 on: June 03, 2022, 06:21:43 AM »
Turns out, after sitting for 4 years, things can get pretty gummed up!  I took the carbs off last night and found that 3 of the 4 pilot jets were almost entirely blocked and 2 of the main jets were completely blocked.  After a good round of carb cleaner and my air compressor, all paths / jets were cleared.  I also hooked up my new CarbTune Pro 4, which I highly recommend to anyone considering getting a tuning tool, in order to balance the carbs.  It was an absolute breeze to get the carbs close to one another as you'll see in the video below.  I still have some work to do but everything is running smoothly and it sounds SO amazing in person.  It's much more throaty / growly than I imagined which was a pleasant surprise (despite this waking up my wife last night).

Next steps are to seal the gas tank portion of my tank, get it mounted and connect the oil lines.  I've got a busy two weeks ahead of me but I hope to take it for its maiden voyage soon.



Offline SOHC4 Cafe Racer Fan

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Re: Pin2Hot's 73 CB750
« Reply #315 on: June 03, 2022, 08:43:30 AM »
That's a nice personal victory, Kevin - tempered by waking up the wife!  Charge on!!
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 Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #316 on: June 05, 2022, 09:17:19 AM »
Hey. Guys. I rode it.


I’ll post an update tomorrow as there’s still some more work to do. But after almost 15 years, I’m able to ride this bike. Huge thanks to everyone here for offering their advice and encouragement.

Also, don't mind the smoke, I hadn't put the plug in for the tach cable and it was shooting oil onto the headers . . .
« Last Edit: June 05, 2022, 09:22:32 AM by Pin2Hot »

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« Last Edit: June 05, 2022, 10:42:18 AM by Godffery »

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #318 on: June 06, 2022, 06:30:05 AM »
Hugely successful weekend.  What a wild ride this entire project has been.  It's almost surreal now being able to put my leg over the bike and know I can go ride it.

There's a handful of items I've uncovered since doing a short 20 minute ride on Sunday.  First of which, install tach cable plug when it arrives.  Second, adjust valves.  I can definitely hear a ticking now on the top end so I'll go through each valve and set lash again which I imagine is pretty standard for a newly built motor, right? 

I also definitely burned up my Antigravity battery.  But I kinda figured it was dead anyway before really using it on the bike.  Way back when I left it discharge too far and I believe I damaged it but decided to use it on the bike anyway.  Either that or I made a mistake wiring up the reg/rec which I have yet to verify is putting the right voltage on the battery.  When I got back I noticed the battery had a small bubbling coming out of one seam and was pretty warm to the touch.  Instead of dropping another $180 on a new one, I think I'm going to get a same size form factory lead acid unit and try that for now.

It's kinda fun learning the quirks of this machine, particularly trying to find neutral after failing to go all the way down to first gear and coming to a stop.  Also hard to remember turning on/off my petcock as I'm used to riding fuel injected bikes and never having to worry about such things.  I'll get used to that. 

So I need a new battery and need to adjust valves before I ride again so I likely won't be out much this week.  I'll also get much better videos of the bike instead of these short clips.  I'll make sure to record the amazing exhaust note of this bike, it's hands down the most glorious sounding bike I've ever owned.

Thanks again to everyone who's helped me get this far.

Super short clip of me leaving on my shake down run.

Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #319 on: June 20, 2022, 10:53:54 AM »
Spent two hours riding yesterday working out all the kinks and BOY are there some kinks.  Fortunately nothing super major but let's just say things got oily.

Made a rookie mistake and overfilled the oil tank.  The bike had sat for a week and most of the oil drained back into the crank case so I stupidly put another quart in.  I let the bike warm up and rode out of my subdivision only to see massive amounts of smoke begin to billow out from the front of the bike.  All of the oil at the bottom of the engine pumped back to the tank and overflowed out of the overflow vent I put in my modified tank.  I, stupidly, haven't connected a hose to that fitting and it poured all over the headers.  I'm lucky it didn't catch fire.  I was carrying a fire extinguisher just in case something like this occurred.  Fortunately the only damage was a trail of oil leaving my neighborhood and an oily engine.

Despite that close call, the bike operates wonderfully.  Fires right up, idles great and pulls hard.  I haven't opened it up yet but I'm pleasantly surprised at the power.

I'll be taking the bike to get it inspected (hopefully) this week so I can ride it without fear of getting impounded and I'm curious to see where it may fail.  Anyone out there know what the big deal breakers are for a motorcycle inspection?  My rear brake doesn't have a brake light switch and my speedometer signal isn't connected.  Otherwise it has all the major components present and they all function properly.

Here's a nice action shot my wife took of my on my way back from family dinner:



Offline Pin2Hot

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Re: Pin2Hot's 73 CB750
« Reply #320 on: August 23, 2022, 08:53:21 AM »
Been dealing with some strange issues on the bike lately and spent a lot of time in the garage last night working through them.  I'd been having weird issues with one cylinder (#3) firing inconsistently with a lot of subtle backfires just coming off of idle.  Digging through a million posts a common theme emerged: check float bowl heights.  I figured since I'd adjusted the float heights way back in the day I was fine. 

I was wrong.  I used the clear tube method to see exactly where the fuel level was and they were WAY off.  I was probably 8-10 mm below the gasket mating surface on all but #1 which was about 5mm below it.

Cylinder #1 showing low level.


I cut up a pneumatic hose fitting and spun it into the float bowl drain port which sealed up nicely.  I shoved some clear tubing on the end of that and it worked great.  I wasn't able to start the bike until this morning but when I did, it IMMEDIATELY started.  I don't think the starter motor went a full rotation before things were firing.  It idles so much better, I'm not having to adjust the idle screw anymore to get it to warm up more effectively.  It just works.

So for anyone actually still reading this struggling with a poorly running bike, check your float bowl levels first, work from there!