Author Topic: '71 cb750 finally runs! and drives!  (Read 4516 times)

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newcbguy

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'71 cb750 finally runs! and drives!
« on: December 02, 2007, 08:50:34 AM »
Well after about 8 months of piecing together my bike I fired it up for the first time yesterday. I was overjoyed when she started to hit and came to life! After It started I checked a few things rebuilt my petcock and put the gas tank on and went for a stroll. At first she wasnt getting any gas and the first run It died before I came up to my drive and I coasted home. After rerouting the fuel line and removing it to clear the air bubble inside she ran great on the second run.  Does anyone have any pointers on fuel line routing? I have automotive 3/8" line and it might be a little larger than stock. I was amazed at how smoothly it idled after only a bench sync. After I get it broken in and get tires and all my lights working I want to go over and adjust the timing and get the carbs vacuum  sync'd. But right now I am happy with a smile plastered on my face! I don't think it would have happened so easily if it weren't for all the knowledge of the forums here, so thanks guys! ;D

here is a video of her starting the first time:
http://www.youtube.com/watch?v=86TFvuaXr1o

here is a pic as of yesterday after the test ride:
http://mysite.verizon.net/carguyjosh/cb750/CIMG1470.jpg


Offline 754

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Re: '71 cb750 finally runs! and drives!
« Reply #1 on: December 02, 2007, 09:43:29 AM »
Cool, have fun with it,........................................


 If you got any riding season left..
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Offline goon 1492

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Re: '71 cb750 finally runs! and drives!
« Reply #2 on: December 02, 2007, 09:45:27 AM »
man you can hear it in the first part of video its tryin to go, congrads. ;D ;D ;D
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Offline 750goes

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Re: '71 cb750 finally runs! and drives!
« Reply #3 on: December 02, 2007, 09:49:42 AM »
There is a little lever on the left side of your carb rack - it is called a "choke"

If you lifted it up a bit I think it may have started just a little bit easier....and it sounds very nice.....



Offline rbmgf7

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Re: '71 cb750 finally runs! and drives!
« Reply #4 on: December 02, 2007, 11:14:17 AM »
lol, for the first minute i watched the video, i could vividly see the choke wasn't on. i just kept saying, "put on the choke! let the bowls fill!"

don't worry, after months of rebuilding and when the day finally comes to start it, even i miss simple little things like that.

nice job!

newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #5 on: December 02, 2007, 12:56:42 PM »
yeah I noticed that after it started finally.  although today setting the choke didnt seem to help, but then again its 80 degrees outside in texas :)

Offline sparty

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Re: '71 cb750 finally runs! and drives!
« Reply #6 on: December 02, 2007, 01:20:09 PM »
Did you rebuild the engine?  If so, did you make sure you had oil pressue first before starting it up?

Looks good, enjoy.

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Offline mcpuffett

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Re: '71 cb750 finally runs! and drives!
« Reply #7 on: December 02, 2007, 01:42:37 PM »
Nice job you have done there  ;), now enjoy it, cheers mick.
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Offline hoodellyhoo

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Re: '71 cb750 finally runs! and drives!
« Reply #8 on: December 02, 2007, 02:27:08 PM »
Congrats!
1972 CB350F (Back from the Dead!)- http://forums.sohc4.net/index.php?topic=20822.0
1965? S65 - Coming Eventually!
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newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #9 on: December 02, 2007, 03:42:45 PM »
yeah the bike has undergone a frame off resto job (which is still happening). Here are some pics of the bike when I first wheeled it into the shop. (barely - the front brake was dragging bad and the tires were flat) The engine was locked up due to the pistons rusted to the cylinders and there was a chisel jammed into a broken and stripped spark plug in the #4 cylinder. Sparty I did make sure that I had oil pressure, I went ahead and installed a gauge on the motor and was relieved to see the needle start moving after cranking a minute or so. I still have quite a bit to do, but its nice to have a runner now.





« Last Edit: December 02, 2007, 03:44:53 PM by newcbguy »

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Re: '71 cb750 finally runs! and drives!
« Reply #10 on: December 02, 2007, 04:23:48 PM »
You ROCK, newguy!  :D :D

Way cool work!

The 71 K1 is a spirited ride, I loved mine. Does that odometer really say 28,000 miles? Wow, that's brand new!

Have you found the other missing parts for it? I see you're missing turn signal lenses, front boots...
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #11 on: December 02, 2007, 05:13:26 PM »
yes I am guessing that its correct at 28k miles as the gauges are correct for the year and the speedo still works. I still have a few main parts to hunt down, but plan to keep the later style fork caps, and I had to modify a 77f rear fender to fit which I got together this afternoon. I would like to find some early style headlight ears or at least some '72 chrome ones, but I dont have a 100 bucks to blow on them. The ones I have are off a '80? or so cb and look nice but im not really liking the large blinkers. I have the stock rear signals and a few spares for parts so I should be able to get that together, but im not sure how I will have the front. Most likely depends on what I can come up with for cheap. Here is a pic of the '77 fender on the back. notice the '71 taillight I made to fit on there. Almost looks original except the wires that pass through the grommet on the fender is visible behind the seat/grab bar by an inch or 2. oh well, at least its not smashed like the original one.




tmart

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Re: '71 cb750 finally runs! and drives!
« Reply #12 on: December 03, 2007, 11:41:21 AM »
Where in Texas are you from,I am in Longview here in east Texas?great sounding first start.congrats
Terry

newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #13 on: December 03, 2007, 12:05:09 PM »
Terry ,

Im over close to greenville, tx about 40-50 miles east of DFW. Any other single cammers over in this area?

Offline UnCrash

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Re: '71 cb750 finally runs! and drives!
« Reply #14 on: December 03, 2007, 05:01:02 PM »
Nice Work,

It's looking great!
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Re: '71 cb750 finally runs! and drives!
« Reply #15 on: December 03, 2007, 07:55:40 PM »
yes I am guessing that its correct at 28k miles as the gauges are correct for the year and the speedo still works. I still have a few main parts to hunt down, but plan to keep the later style fork caps, and I had to modify a 77f rear fender to fit which I got together this afternoon. I would like to find some early style headlight ears or at least some '72 chrome ones, but I dont have a 100 bucks to blow on them. The ones I have are off a '80? or so cb and look nice but im not really liking the large blinkers. I have the stock rear signals and a few spares for parts so I should be able to get that together, but im not sure how I will have the front. Most likely depends on what I can come up with for cheap. Here is a pic of the '77 fender on the back. notice the '71 taillight I made to fit on there. Almost looks original except the wires that pass through the grommet on the fender is visible behind the seat/grab bar by an inch or 2. oh well, at least its not smashed like the original one.





I have a nice rear fender from a K3/K4, and some rusty-ish headlight ears (if I didn't throw them out). You can have them for shipping, if you want. I don't remember which style taillight it had. It came from a drag bike that was a mix of K3/4/1 years.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline GoatBaSS

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Re: '71 cb750 finally runs! and drives!
« Reply #16 on: December 04, 2007, 06:54:36 AM »
No, NO No! You got all the polishing wrong! Come on over to my place and you can "practice" on mine! :D
Looks Good!
Leethal # 3046?
1972 CB750K/900CC Red Headed Dunstall, 1975CB750FSS Gone BNF: 1974CB500T, 1976CB750K X 2

newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #17 on: December 04, 2007, 07:00:03 AM »
hondaman, - are those the painted fork ears that you are talking about? I have a set of rusty ones from a junk  front end I bought and I just got a left one from e-bay that is usable. Im not sure the junk ones I have can be saved. If you have the painted fork ears that can be used I would love to take them off your hands! Also would the headlight and left control not being hooked up cause the charging voltage to be abnormally high? I have gone and installed a dohc rectifier/regulator combo and tried to replace all the connectors with the gold plated ones from Z1, but on my new charged battery the other day I was checking the voltage on the battery and noticed about 12.6 with the bike off. with the bike on about 3k rpm it showed about 17 volts! I checked last night and got 12.4 with the bike off and then checked between the green and black on the regulator and got about 11.8 volts there. that doesnt seem like alot of drop to me? I dont want to fry my new battery, is there anything else I can check? Or maybe I need to install the rest of my electrics and then worry about it?

Offline andy750

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Re: '71 cb750 finally runs! and drives!
« Reply #18 on: December 04, 2007, 07:21:35 AM »
I have a chrome chain guard for you if you want to cover that chain! I got it off Ebay but wasnt happy with it - you may find it suitable. Yours for the cost of shipping - around $12. Should fit your bike - was listed as a 72 chain guard.

cheers
Andy
Current bikes
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2. CB750/810cc K2  - road racer with JMR worked head 71 hp
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Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #19 on: December 04, 2007, 03:19:27 PM »
goatbass, There is no joy greater than having black polish up to your elbows and numb fingers! On another note, does anyone have any experience with the dohc rectifier conversion? I've got it working but apparently something is wrong because its overcharging.

Offline GoatBaSS

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Re: '71 cb750 finally runs! and drives!
« Reply #20 on: December 05, 2007, 04:57:37 AM »
 ;D
I am an electronic rectifier type myself, no luck there.
Irishguy, you out there? Can you weigh in on this? I think he was replacing one he got @ Barbers. May be of some help.
Leethal # 3046?
1972 CB750K/900CC Red Headed Dunstall, 1975CB750FSS Gone BNF: 1974CB500T, 1976CB750K X 2

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Re: '71 cb750 finally runs! and drives!
« Reply #21 on: December 05, 2007, 07:55:53 PM »
hondaman, - are those the painted fork ears that you are talking about? I have a set of rusty ones from a junk  front end I bought and I just got a left one from e-bay that is usable. Im not sure the junk ones I have can be saved. If you have the painted fork ears that can be used I would love to take them off your hands! Also would the headlight and left control not being hooked up cause the charging voltage to be abnormally high? I have gone and installed a dohc rectifier/regulator combo and tried to replace all the connectors with the gold plated ones from Z1, but on my new charged battery the other day I was checking the voltage on the battery and noticed about 12.6 with the bike off. with the bike on about 3k rpm it showed about 17 volts! I checked last night and got 12.4 with the bike off and then checked between the green and black on the regulator and got about 11.8 volts there. that doesnt seem like alot of drop to me? I dont want to fry my new battery, is there anything else I can check? Or maybe I need to install the rest of my electrics and then worry about it?

This sounds a lot like a bad ground.
Look under the seat: there should be a small green wire with a ring terminal attached to the seat lock bracket. This is the main "system ground", and if it gets dirty/corroded, the whole system's voltage will seem to read wrong. Clean it up and reinstall with a drop of oil or bit of light grease on it.
Then, look at the condition of the big ground cable that goes from the battery to the left side of the engine, at the engone mount bolt. Make sure the bolt and ring connector are in excellent, clean condition, then treat as above to reassemble.
Finally, check the condition of the white, 6-circuit plug that goes down into the left rear of the engine: this is the alternator connection. Often, the contacts are in poor condition, causing loss of phase reference for one or more circuit returns. These can be slipped out the back of the connector, using a tiny screwdriver to bend in their tiny lock tabs, then clean, lightly oil, rebend the tiny tab out a bit, and snap back in. One at a time, please, so they don't get mixed up! If they are burned, file lightly with a jeweler's file until they shine, then grease instead of oil on reassembly, to keep the air out. Silicone grease works, too.

Finally, remove the cover from the voltage regulator. Make sure the little contact arm is free to move up and down. These can corrode into the HIGH position, making for high battery voltage and a dried-out battery. Make sure the contacts (they look like points) are clean and shiny, too. DON'T oil the contacts, except with LPS-1 (or nothing else). If it's all corroded up in there, get another one. The voltage across the battery at 3k RPM should max out at 15.8 volts with the lights off, 13.4 volts minimum. If measuring from battery + to ground is more than from battery + to -, then ground cables and connections are the culprit.

These are very simple charger systems: don't let it outfox you! The "regulator" is supposed to "rest" at HIGH CHARGE, only pulling the little contact down for overvoltage. When pulled down, it reduces the alternator output. So, when the voltage goes above 15 volts or so, the little coil pulls in to reduce the alternator's power. Increasing the spring tension in the "regulator" makes it stay "resting" until a higher voltage overpowers the spring, so the voltage in the system rises a little more before the coil can pull in. That's all it does!

My extra fork ears are gone: I must have given them away already. Sorry!
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

newcbguy

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Re: '71 cb750 finally runs! and drives!
« Reply #22 on: December 06, 2007, 02:21:33 PM »
I just saw your reply on this Hondaman, When I got the bike It did not have a ground running from the engine to the battery negative. The negative from the battery ran to the bolt for the tool tray hold down and looks factory. When I reinstalled everything I put it back this way as well. I would imagine that the engine is grounded through the mounts to the frame no? The wiring harness I used had a green wire which was cut off back in the harness that lead to the rear brake light/turn signals. I put a ring terminal on it and grounded it to the seat latch after scraping the paint off the frame to make good contact. I dont remember putting bulb grease on it though? The rectifier/regulator I have is from an '81 cb900, as I wanted to replace my shabby looking stockers that have been overheated and misused.
I followed the hand drawn wiring diagram that is floating around here to hook it up . The other day I unhooked the regulator from this and hooked up the stock regulator which made the voltage drop to 12 volts at idle and above. not sure if it was working correctly or not.  Can i test the regulator to see if its getting enough voltage from the battery?  Im going to go check that ground.

here is a picture of my electical configuration: I put in a new connector to connect the reg/rect to the wire harness but didnt replace the one to the alternator. I did however clean the contacts and put bulb grease on them.

« Last Edit: December 06, 2007, 02:26:57 PM by newcbguy »

Offline GoatBaSS

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Re: '71 cb750 finally runs! and drives!
« Reply #23 on: December 06, 2007, 06:51:08 PM »
Look over the ground at the seat lock as Hondaman mentioned, it knocked me out of the running for a long time on a previous bike.
Leethal # 3046?
1972 CB750K/900CC Red Headed Dunstall, 1975CB750FSS Gone BNF: 1974CB500T, 1976CB750K X 2

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Re: '71 cb750 finally runs! and drives!
« Reply #24 on: December 06, 2007, 07:09:55 PM »
I just saw your reply on this Hondaman, When I got the bike It did not have a ground running from the engine to the battery negative. The negative from the battery ran to the bolt for the tool tray hold down and looks factory. When I reinstalled everything I put it back this way as well. I would imagine that the engine is grounded through the mounts to the frame no? The wiring harness I used had a green wire which was cut off back in the harness that lead to the rear brake light/turn signals. I put a ring terminal on it and grounded it to the seat latch after scraping the paint off the frame to make good contact. I dont remember putting bulb grease on it though? The rectifier/regulator I have is from an '81 cb900, as I wanted to replace my shabby looking stockers that have been overheated and misused.
I followed the hand drawn wiring diagram that is floating around here to hook it up . The other day I unhooked the regulator from this and hooked up the stock regulator which made the voltage drop to 12 volts at idle and above. not sure if it was working correctly or not.  Can i test the regulator to see if its getting enough voltage from the battery?  Im going to go check that ground.

here is a picture of my electical configuration: I put in a new connector to connect the reg/rect to the wire harness but didnt replace the one to the alternator. I did however clean the contacts and put bulb grease on them.


No, the engine does not ground through the frame. It must have a separate, low-resistance ground cable from the top left bolt on the back of the engine, up to the battery negative, IN ADDITION to the little green wires in the harness. This is the "base ground" for the alternator. You should be able to see this wire on many pictures of the left sides of the other 750s here on the board: a junkyard would probably sell you a used one for a buck. It's real important! The theory behind this method is a little involved (TT has covered it in several posts I've seen here), but trust me, it's needed.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com