Author Topic: Dorothy III - CB750  (Read 45488 times)

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Online 70CB750

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Dorothy III - CB750
« on: April 28, 2011, 05:37:57 am »
The motorcycle was free from a friend, based on his story, he got it himself for free in 2009 and got it running after who knows how many years.
This year, the space got more important than another bike - he has few others - and he gave it to me.

This is what  it looked like when I brought it home - without foot rests from the front of the frame, I removed those right away.

The bike is younger than me, not sure if it's a good or bad thing ;D
« Last Edit: November 02, 2011, 03:13:09 am by 70CB750 »

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Re: CB750 made in March, 1970
« Reply #1 on: April 28, 2011, 05:45:23 am »
I took out  all carburetors and broke the aluminum stay in the proces >:(  Also had to cut the throttle lines, I wanted to replace them any way and carburetor slides were pretty much stuck.

Anway, I just cleaned them and put back together, compare to the infamous craperator Carter BBD they are piece of cake.  Well, not sure yet, we will see how it runs.

The goal is to get it inspected and on the road this spring.  Fussing around it I found the top triple tree bracket cracked.  Looking for replacement was interesting.  Carpy had one already polished for hundred bucks,  neanderthal would sell me unpolished for 130:) -  I ended up buying for much less 74 vintage from ebay and it fits just fine.

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Re: CB750 made in March, 1970
« Reply #2 on: April 28, 2011, 05:48:46 am »
I could not resist and practiced aluminum polishing on the old bracket.    In the jeep world, I avoid blings-blings completely, but here it just seems to make sense.

I have a dedicated buffer and set of sawn wheels and rouge - it works and it is quite fulfilling process:)  The polished part is the one reflecting the flash.

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Re: CB750 made in March, 1970
« Reply #3 on: April 28, 2011, 05:52:26 am »
The oil tank does not seem to be stock or  the year 1970, but what do I know.  Ideas, anybody?

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Re: CB750 made in March, 1970
« Reply #4 on: April 28, 2011, 05:54:03 am »
The seat is pretty much shot and it broke the fender in the process.    I bought yellow MotBat, seems to have good reviews.

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Re: CB750 made in March, 1970
« Reply #5 on: April 28, 2011, 05:56:10 am »
I found new headlight - it takes H4s, not sure what year, but it surely looks better than the last one. 

Yes, those bolts are torx from jeep rollbar, they are temporary.

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Re: CB750 made in March, 1970
« Reply #6 on: April 28, 2011, 06:00:02 am »
There was a bunch of weird jumpers connecting the ground of coils, battery and the engine.  I took some out and replaced others.

Also trying to fit in some small fuel filters, the tank had brown guey  like honey in it - proly the old gas.  I cleaned it with Purple Power, looks like it worked, but I still want to clear the gas before it enters the carbs.

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Re: CB750 made in March, 1970
« Reply #7 on: April 28, 2011, 06:03:52 am »
This is where it stopped for now.  The petcock - btw, my wife was surprised a bit, when I told her I have problems with my petcock ;D - was pretty  much shot, I replaced the packing, but the bowl was chewed up from - I guess - vicegrips and eventually developed a leak.  Gotta get replacement.

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Re: CB750 made in March, 1970
« Reply #8 on: May 04, 2011, 08:15:53 am »
Got a new petcock from Vintage CB750 and replaced the leaky one. Installed the tank and the very right carb is overflowing.

Connected + on the battery and tried to start it anyway.

It didn't start or even coughed, but the battery works well:) - lot of turning.

The oil light went off - good sign, it builds and holds oil pressure.

Checking for spark, the spark plug I pulled out has cracked porcelain right under the electrode, I don't think it makes a difference, but I will replace all of them anyway,  piece of porcelain in the engine is not a good thing.

Used the new petcock to shut the gas, dropped the bowl from the very right carburetor and sure enough the valve above floater was stuck.   Pulled floater and the valve and cleaned it with fine scotchbrite and carb cleaner,  looks like it works now, but only cranking will tell.
« Last Edit: May 04, 2011, 08:29:58 am by 70CB750 »

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Re: CB750 made in March, 1970
« Reply #9 on: May 04, 2011, 09:22:10 am »
Did you get spark? Check the position of the kill switch, is it on or off? Cliff.

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Re: CB750 made in March, 1970
« Reply #10 on: May 05, 2011, 08:56:07 am »
Thanks, Magpie.

I replaced plugs today,  #3 cable broke on me, but it started and I moved it around little bit on it's own power.  The carbs are a mess for sure, but I have to address the coils and cables first.

Also the ignition switch is so warn out it's hard to tell if it is on or not.  Moves Off to On freely,  I am going to replace that too.

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Re: CB750 made in March, 1970
« Reply #11 on: May 16, 2011, 08:28:21 am »
Bypassed the kill switch, new one will be needed but this will do for now.
Replaced points with PAMCO and coils with Ultimate coils from Vintage.

It took me a while to figure out wiring for coils -  http://forums.sohc4.net/index.php?topic=89093.0 - but after finally grasping the elementary information (points signal is (-):))  I got it wired.

It actually started, but run rough and kept dying on me.  I took it on the road  anyway and went half a mile one way, turned around and came back.  Got cocky and passed the house and went in the other direction and that's where it died on me and it would not start.  Battery dead, pushed it home.

Decided to buy charger/floater and go over carburetors one more time.  The speedo is working but tachometer is not. 

Impact screwdriver got the tacho cable screw out, but the cable is in two pieces, gotta get a replacement.

Positive note - the neutral light works.

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Re: CB750 made in March, 1970
« Reply #12 on: May 18, 2011, 10:41:53 am »
Started it up on 5/17/11 and took it up and down our road several times.  Everything was fine and dandy and than suddenly I felt it lost power.  Pulled in the driveway and sure enough it would not idle.
Took it to the shop and it eventually started but the #4 - all the way to the right - is running much hotter than the rest.  Anyway took out PAMCO, cleaned the T|F|  marks and checked and adjusted timing.

Now for #4 - I think it is in the carb.

Interesting thing - with the air filter off if I hold my hand on the suction of every other cylinder  it just slows the engine a bit. but if I close the intake on the #4 it shuts down the engine.

Am I just an idiot and only the #4 is running?  Suggestions appreciated, next action when I buy new tachometer cable.

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Re: CB750 made in March, 1970
« Reply #13 on: May 18, 2011, 10:45:06 am »
Checked carburetors and sure enough, number 2 bowl was empty.  The valve the floater holds was stuck.  Took it out, cleaned it and polished with 3M Scotch pad, put it back together, started nicely with choke and now correctly set timing. 

Took it up and down the road several times, runs ok, lost rubber from the left peg.

New issue - oil leak from the seal behind the chain sprocket, gotta change it.  It is a steady drip every second, makes quite a puddle reaaaaaaallly quick.

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Re: CB750 made in March, 1970
« Reply #14 on: May 19, 2011, 09:34:02 am »
Ordered  tachometer cable from Manassas Honda, met Drew  :)

Took of the sprocket cover, chain cover and sprocket, the oil seal fell out on it's own.  Apparently it was loose.   Inspection revealed nothing wrong with it,  cleaned it, greased it and pressed it back in;  I wonder if it's gonna stay.

Now to measure the chain and see how far stretched it is.

Also the drive is  16:44 = 2.75  to compensate for the 16" rear wheel. 

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Re: CB750 made in March, 1970
« Reply #15 on: May 19, 2011, 09:54:22 am »
DANGER DANGER!  On the top triple clamp: there are spacers that go in the gap of the clamp on each side. They keep that clamp from being drawn too tight and breaking like your original one. If you don't have those spacers, STOP, and loosen the clamps and get the spacers. That triple tree is no longer available and routiinely sells for more than $150, like $300+. You were only LUCKY that you found one for less. The spacers may not be available any more either, they can be made from head nut washers. Standard hardware washers are too thin and the triple will still crack.

Edit: Since you don't have the stock instrument mounts, you can get away with a later model top clamp that would be cheaper than the original, and very rare "Unicorn" style that your bike should have.

As to the oil tank, it appears stock. The early tanks were slab sided, no emblem dimples.
« Last Edit: May 19, 2011, 09:58:41 am by MCRider »
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"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

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Re: CB750 made in March, 1970
« Reply #16 on: May 19, 2011, 11:19:05 am »
Thanks, MCRider.   The original clamp was cracked with the spacer there - and I installed it with spacers again.  The spacers looked like a washer with one side flat.

Thanks for the info on the tank:)

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Re: CB750 made in March, 1970
« Reply #17 on: May 19, 2011, 11:29:41 am »
Thanks, MCRider.   The original clamp was cracked with the spacer there - and I installed it with spacers again.  The spacers looked like a washer with one side flat.

Thanks for the info on the tank:)
That's right, sounds like you're good.

I've seen too many of those get broken (many on this forum) and the early ones with the Unicorn horn get rare and expensive.
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

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Re: CB750 made in March, 1970
« Reply #18 on: May 26, 2011, 09:27:42 am »
Got a new tacho cable from Manassas Honda - met Drew too  :)

Installed and started and it idled way too high,  gotta admit I doubted the tacho since it is a little #$%*ty aftermarket. 

Today I dedicated to it few hours. Since the-one-who-must-be-obeyed has a problem with me taking the bike on the road I drove it round my vineyard about fifteen times, seems like one round is 100 yards, LOL.

Frankly, I don't blame Sharon for the input,  the bike does not have a license, safety inspection, nothing.  And I have valid VA license for a car and only Czech and International license for motorcycle :)

Anyway,  the idle was high and there was no logic to it, finally I found out the throttle cable is binding under the tank for #1 and #4 - that explains a lot.   I will  reroute the cable and try again, but with the tank lifted higher I got it to idle round 1000 just by ear.

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Re: CB750 made in March, 1970
« Reply #19 on: May 26, 2011, 11:22:03 am »
Got a new tacho cable from Manassas Honda - met Drew too  :)

what's up local buddy?

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Re: CB750 made in March, 1970
« Reply #20 on: May 26, 2011, 11:24:50 am »
SNIP

Anyway,  the idle was high and there was no logic to it, finally I found out the throttle cable is binding under the tank for #1 and #4 - that explains a lot.   I will  reroute the cable and try again, but with the tank lifted higher I got it to idle round 1000 just by ear.
Actually, that is the logic. A high idle is often caused by the throttle cable being poorly routed. Also, aggressive use of tie wraps on the cable can hang it up. Glad you found it.
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Re: CB750 made in March, 1970
« Reply #21 on: May 26, 2011, 11:54:18 am »
Hey, Charlie, doing great.  It will be road ready one day:)

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Re: CB750 made in March, 1970
« Reply #22 on: May 26, 2011, 12:11:21 pm »
Hey, Charlie, doing great.  It will be road ready one day:)

haha same here. having 4 motors and 2 frames hanging from the ceiling is a bit depressing but I just look ahead at what it can be and that keeps me going.

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Re: CB750 made in March, 1970
« Reply #23 on: June 14, 2011, 05:49:36 pm »
Found some gunk in carburetor slides, cleaned it with scotchbrite.

Looks like the cable was not the reason of hanging slides,  4 days in a row the bike now starts with choke, warms up and idles nicely around 1000.  It is not perfect yet, before vacuum gauge synchro, but messing with it every day does wonders for my ability to tune the stop screw and air screw.

There was rusty gunk in the petcock bowl, cleaned it out.

Side note:  I landed a job after 9 month, life is great.

Naughty note:  The other day, while sitting on the bike, adjusting stop screws on #2 and #3 and checking for reaction, I realized it reminds me working clitoris, same small finger movements   - now where is the damn G point?  ;D ;D

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Re: CB750 made in March, 1970
« Reply #24 on: June 18, 2011, 09:15:03 am »
# 4 carburator will not go over -15 of vacuum.  The other three I was able to tune to somewhat same reading - 22, but this one just will not go up.

I wonder why, and also the needle movement was excessive at least - maybe it has not stock cam, not sure how to find out.

Checked voltage and with revs up it is out of the chart - like 17V for 5 000 or so.  Will run it with headlight on from now on, looks like it is time for Oregon motorcycle parts.

 

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