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Author Topic: Dorothy III - CB750  (Read 48754 times)

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Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #50 on: September 12, 2011, 11:07:50 pm »
Dug into controls wiring and found fried wire in the right handlebar.  The one that gets power to the kill switch.    The spring from the light switch jumped out and got lost somewhere in hay and horse manure.

Made my mind and bought R6 controls on ebay, tried Mikes first, but clutch side was on back order and R6 are much cheaper too.

Controls came yesterday, I like them already, will have to decode wiring - my bike is much more simple than R6.




Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #51 on: September 16, 2011, 06:22:01 pm »
Hi/Low switch is for R6 on the left, unlike 70CB.  Also 70 CB has Off/Hi/Low and R6 has Low on all the time and High comes on as addition (two reflectors)

Took me a while, but as always - take it apart and solution will present itself.  The H/L switch has two wires but it has space for three - soldered on one more wire, problem solved.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #52 on: September 16, 2011, 06:28:15 pm »
Now the low beam will come on with ignition - I can live with that - and high beam is optional, but low beam is off when high beam is on.   Hmm, confusing.

Offline MCRider

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Re: CB750 made in March, 1970
« Reply #53 on: September 16, 2011, 06:51:46 pm »
I believe that is correct. High beam filament is independent of low beam. They don't run together.

I seem to remember if you slid the switch slowly you'd find a sweet spot where both filaments light. Sweet. Probably burn up the switch if left there.
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
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Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #54 on: September 17, 2011, 05:01:33 am »
Makes sense, from looking at the innards it would proly touch either contact on slight jump - nothing desired IMHO. 

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #55 on: September 19, 2011, 06:17:46 am »
Controls are on,  sorting out wiring was easier than I imagined;  it all works now.

The throttle from Honda works with the right control, all it takes is to cut a thread 10x1.25  for the throttle line.   The hole in the control is square and plastic, but the thread is cut, seems to be holding.  The original plan was to lathe an insert and epoxy it in, I may still do that down the road.

In the process I stepped on hot soldering iron with bare foot - quite glad nobody watched me dance and curse  ;D

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #56 on: September 22, 2011, 04:50:13 am »
Installed carburetors, tygon lines and the tank on Tuesday.   It eventually started, run like crap, call it a day.

Later realized 1-4 coil cables were disconnected to access the wiring, that poor girl run on two cylinders just to please me.

Went back, on all four she runs quite well, thank you.

Next day - the Tuesday 9/20 - she started nicely with a touch of choke.  Put license plate on her and drove her round the neighborhood for 5 miles.  First time legally, she shifts well, runs nicely and idles much better after few miles.  She needs to run and run, nothing is better for the engine than miles and miles of use.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #57 on: September 26, 2011, 03:03:16 am »
Rode her for 60 miles, got wet in a storm, seafoam and filled the tank at the gas station for the first time. 

#4 was skipping from time to time, could be the odd angle the right two carbs are sticking up - I have to heat up the boots and adjust that, but new carb stay would help too, I am sure.

Got two good wheels with decent tires, going to install them as soon as I get new chain and sprocket combo.

My Spaceballs 1 picture.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #58 on: September 27, 2011, 03:12:53 am »
Rode to work.

Pulled two right carb boots and soaked them in xylol. 


Also repositioned shocks, there was this odd bazmek by the wheel to make them shorter; basically the lower mounting point was all the way back by the chain tensioner.  Gotta take a picture.

Offline lucky

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Re: CB750 made in March, 1970
« Reply #59 on: September 29, 2011, 08:58:08 pm »
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.

"Pulled floater and the valve and cleaned it with fine scotchbrite and carb cleaner,  looks like it works now,"

It will probably leak and over flow. You should have replaced the float valve, The rubber tip gets hard,out of round and can even be missing a chunk.
You have to look at them with a magnifying glass. But you still have to replace them ....unless you have a rubber hardness tester, and a out of round rubber cone measuring device LOL....LOL

Just go get 4 new float needles and let those 30 year old rubber tipped needles go back to mother earth where they came from.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #60 on: September 30, 2011, 03:13:54 am »
My float needles are metallic, no rubber.

Anyway, I already got 4 rebuild kits and all the jets and valves are new in all carbs.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #61 on: October 03, 2011, 03:15:50 am »
Rented a tester from Autozone for the compression check:  she pumped me 140 on cylinder one and 140 on cylinder two; than I had to mess with my home made adapter to be able too get it in # 2 and 3.

The next version of the adapter gave me 70, 70, 65, 70 -  I used part of rubber hose.   That got me inspired and I dedicated few hours making an all steel adapter and that's how I got to final numbers L to R:

120, 120, 130, 120  and I am happy with it.

Back in June I did compression test with tester from Autozone and got readings around 35, that was weird.  The difference is either due to the fact that this time the tester was brand new. still wrapped in or/and because I rode it 100+ miles. 

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #62 on: October 07, 2011, 02:24:07 am »
Soldered #1 float and weighted all of them on my reloading scale:

       [grains]
1. - 165.1
2. - 157.6
3. - 161.1
4. - 162.5

assembled and adjusted float levels.

Got aluminum  stock for the carb stay and also for the air filter, measured and drilled pilot holes.  Need to buy some hole saws,  proly better to drill it on the lathe, much more precise than the cheap drill press.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #63 on: October 12, 2011, 04:07:41 am »
Got it running on Sunday.  Clean carbs, fresh fuel - looks like the culprit was too much of seafoam in the tank for the cold engine to start.  I will never know.

After a while there was odd sound and #1 car boot had a crack in it.  Ordered new ones, there is nothing I can do with it.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #64 on: October 12, 2011, 04:11:27 am »
Last night I made replacement stay for carbs.  Used rolled aluminum, hole saw, sender and scotch pad, turned out OK.

Also made a copy of the only key I have - from Access blank # 62.  It took about 30 minutes of careful copying and filing, but now I have a spare key.

Started working on the air filter, the aluminum tubing I have is too thin to use screws to secure it to carbs, will have to use rubber sleeves and clamps.  The piece of aluminum is from sunbrella I found in local trash yard, it has the right size for my purpose.
« Last Edit: October 12, 2011, 05:34:40 am by 70CB750 »

Offline Old Scrambler

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Re: CB750 made in March, 1970
« Reply #65 on: October 15, 2011, 12:53:57 pm »
You had better be prepared to make a few more of those carb racks..............others are looking!  And the oil pressure adaptor is fine.........maybe add a few shallow groves to give it a 'finned' look.

I like your pratical approach to solving the problems............now if only you had read the shop manual!
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Offline Magpie

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Re: CB750 made in March, 1970
« Reply #66 on: October 15, 2011, 07:03:24 pm »
very nice! What size of countersink did you use for the holes for the screws connecting the carbs to the plate please and thanks. Cliff

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #67 on: October 15, 2011, 07:17:17 pm »
very nice! What size of countersink did you use for the holes for the screws connecting the carbs to the plate please and thanks. Cliff

The counter sink bit did not like the aluminum.   Something about cutting angle or maybe it was just dull.  I used 1/2" drill bit to sink those screw heads, it worked fine.

I wish for a mill more than ever.  The drill press is OK, but the level of precision is frustrating at times.

Offline Magpie

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Re: CB750 made in March, 1970
« Reply #68 on: October 15, 2011, 07:20:04 pm »
Thanks! I had my nephew make one up for me and got stopped by the countersink. I guess you drilled a bit then checked the depth with the screw and repeated as necessary. Nice job! Cheers, Cliff.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #69 on: October 17, 2011, 03:04:01 am »
You had better be prepared to make a few more of those carb racks..............others are looking!  And the oil pressure adaptor is fine.........maybe add a few shallow groves to give it a 'finned' look.

I like your pratical approach to solving the problems............now if only you had read the shop manual!

Thank you, I do what I can:)  The oil adaptor is the first take, one of those things I will do again when I have time  ;D   

Shop manual?  What is it?

Offline lucky

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Re: CB750 made in March, 1970
« Reply #70 on: October 17, 2011, 08:26:05 am »
My float needles are metallic, no rubber.

Anyway, I already got 4 rebuild kits and all the jets and valves are new in all carbs.

The all metal float needles were the worst.
If you look at a metal float needle and you see a shinny ring on the tapered part it is no good.
What happens is the engine vibration on the steel tapered part of the needle vibrates against the brass part and then it leaks because the cone shape of the needle is not concentric and can spin in the tapered hole of the float needle seat.

THAT IS WHY Honda changed to rubber tipped float needles.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #71 on: October 19, 2011, 03:15:55 am »
I went through all five carburetor needle positions last night - change it, ride it, repeat.  It was very educational.  Took it for a longer ride afterwards in the dark, quite a night it was.

When I got back I was still pumped - so I changed the brake fluid in  the front brake.   I live the wild life.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #72 on: October 20, 2011, 06:02:26 am »
Looks like needles could go to position 4 from the current 3 - i.e. richer in mids.  There is a touch of hesitation in 4th gear.  Will experiment.

Of course, this is nothing but exercise and education - after replacing pods it will be back to square one.

The filter is coming, used B&D mouse to sand the aluminum and it actually takes and holds 3M scratch pads, works like a charm as the last step before buffer.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #73 on: October 24, 2011, 10:05:29 am »
Replaced plugs with NGK 7, they are wormer and could help with starting. She likes,to my surprise,  full choke on to idle when cold.

Offline 70CB750

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Re: CB750 made in March, 1970
« Reply #74 on: October 26, 2011, 04:04:51 pm »
Warmer plugs and needles on #4 - feels like new bike.  Met an old timer at Shell gas station today - he has quite few Hondas too.

Started to keep a log on gas and milage   means she is no longer in testing.

 

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